\r\n\tThe human microbiota consists of a wide variety of bacteria, viruses, fungi, and other single-celled animals that live in the body while microbiome is the name given to all of the genes inside these microbial cells. Recently, there has been renewed interest in the role played by microbiota and microbiome in both human health and human disease. A correct equilibrium between the human host and their microorganisms is important for an appropriate physiological function. \r\n\tMicroorganisms have evolved alongside humans and form an integral part of life, carrying out a range of vital functions. They are implicated in both health and disease, and research has found links between bacterial populations, whether normal or disturbed, and the following diseases: asthma, cancer, diabetes, obesity, heart disease and, neurological and neurodegenerative diseases. \r\n\tThe chapters of this book aim to present outstanding research on biochemical, genetics, clinical, molecular and behavioral fields about microbiota-gut-brain axis with emphasis in how neuropeptides such as brain derived factor (BDNF), substance P, calcitonin gene-related peptide and neuropeptide Y (NPY), vasoactive intestinal polypeptide, somatostatin and corticotropin-releasing factor are also likely to play a role in the bidirectional gut-brain communication. In this capacity they may influence the activity of the gastrointestinal microbiota and its interaction with the gut-brain axis. \r\n\tIt will be shown evidence that neuropeptides represents a challenge in understanding the complex interactions between gut and brain. Although their precise role in the microbiota-gut-brain axis has not yet been defined, neuropeptides play an important role in this respect. For instance, a growing field of work is implicating the microbiota-microbiome in a variety of psychological processes and neuropsychiatric disorders. These include mood and anxiety disorders, neurodevelopmental disorders such as autism spectrum disorder and schizophrenia, and even neurodegenerative disorders such as Alzheimer’s and Parkinson’s diseases. These brain disturbances have been linked to molecular and biochemical alterations in the course of neurodevelopment so, the research in this area has established different approaches (nutritional, immunological, energy homeostasis), to find the role played by the gut microbiota-microbiome in the etiology of the aforementioned brain disorders.
",isbn:null,printIsbn:"979-953-307-X-X",pdfIsbn:null,doi:null,price:0,priceEur:0,priceUsd:0,slug:null,numberOfPages:0,isOpenForSubmission:!1,hash:"2c441b6a49e0eba12af16fcb6ad8b887",bookSignature:"Dr. Sandra Morales-Mulia",publishedDate:null,coverURL:"https://cdn.intechopen.com/books/images_new/8940.jpg",keywords:"Gut-Microbiota, Neurodevelopment, Synaptic plasticity, Neurogenesis, Neuroimmune system, Neuropeptide Y, Brain-derived neurotrophic factor (BDNF), Peptide YY, Cholecystokinin (CCK), Corticotropin-releasing factor (CRF), Substance P, Neuropeptide Y (NPY), Oxytocin",numberOfDownloads:null,numberOfWosCitations:0,numberOfCrossrefCitations:null,numberOfDimensionsCitations:null,numberOfTotalCitations:null,isAvailableForWebshopOrdering:!0,dateEndFirstStepPublish:"May 24th 2019",dateEndSecondStepPublish:"June 14th 2019",dateEndThirdStepPublish:"August 13th 2019",dateEndFourthStepPublish:"November 1st 2019",dateEndFifthStepPublish:"December 31st 2019",remainingDaysToSecondStep:"2 years",secondStepPassed:!0,currentStepOfPublishingProcess:5,editedByType:null,kuFlag:!1,biosketch:null,coeditorOneBiosketch:null,coeditorTwoBiosketch:null,coeditorThreeBiosketch:null,coeditorFourBiosketch:null,coeditorFiveBiosketch:null,editors:[{id:"287114",title:"Dr.",name:"Sandra",middleName:null,surname:"Morales-Mulia",slug:"sandra-morales-mulia",fullName:"Sandra Morales-Mulia",profilePictureURL:"https://mts.intechopen.com/storage/users/287114/images/system/287114.jpeg",biography:"EDUCATION AND DEGREES \n1988-1991. National Autonomous University of Mexico (UNAM). School of Sciences. B. S. in Biology. \n1995-1997. National Autonomous University of Mexico (UNAM). Cell Physiology Institute. Master in Basic Biomedical Sciences Research\n1998-2000. National Autonomous University of Mexico (UNAM). Cell Physiology Institute. PhD in Biomedical Sciences (Neuroscience) \n2002-2004. Postdoctoral Fellow. Laboratory of Cell Biology: Mitosis, Ciliogenesis, Intracellular Transport and Motor Protein Functions. University of California, Davis- Dept. of Molecular & Cellular Biology, One Shields Ave. Davis, CA 95616. \n2005-2008. Postdoctoral Fellow. Laboratory of Neuropharmacology. National Institute of Psychiatry “Ramón de La Fuente Muñiz”. Calzada México-Xochimilco #101, Col. San Lorenzo Huipulco, CP 14370 México City, México. \n2009-present. Teaching Professor in Biochemistry. Bachelor in Biology Program. School of Sciences. National Autonomous University of Mexico (UNAM). Av. Insurgentes Sur 3000, Circuito Exterior. Ciudad Universitaria, Mexico D.F. C.P. 04510.\n2006-present. Consultant and Assessor Researcher. \nLaboratory of Psychiatric and Neurodegenerative Diseases. National Institute of Genomic Medicine (INMEGEN-SAP). Periferico Sur 4809, Arenal Tepepan, 14610 México City, México.\nLaboratory of Molecular Basis of Addictions. National Institute of Psychiatry RFM, Mexico City, Mexico.",institutionString:"National Autonomous University of Mexico",position:null,outsideEditionCount:0,totalCites:0,totalAuthoredChapters:"1",totalChapterViews:"0",totalEditedBooks:"0",institution:{name:"National Autonomous University of Mexico",institutionURL:null,country:{name:"Mexico"}}}],coeditorOne:null,coeditorTwo:null,coeditorThree:null,coeditorFour:null,coeditorFive:null,topics:[{id:"18",title:"Neuroscience",slug:"life-sciences-neuroscience"}],chapters:null,productType:{id:"1",title:"Edited Volume",chapterContentType:"chapter",authoredCaption:"Edited by"},personalPublishingAssistant:{id:"301331",firstName:"Mia",lastName:"Vulovic",middleName:null,title:"Mrs.",imageUrl:"https://mts.intechopen.com/storage/users/301331/images/8498_n.jpg",email:"mia.v@intechopen.com",biography:"As an Author Service Manager, my responsibilities include monitoring and facilitating all publishing activities for authors and editors. From chapter submission and review to approval and revision, copyediting and design, until final publication, I work closely with authors and editors to ensure a simple and easy publishing process. I maintain constant and effective communication with authors, editors and reviewers, which allows for a level of personal support that enables contributors to fully commit and concentrate on the chapters they are writing, editing, or reviewing. I assist authors in the preparation of their full chapter submissions and track important deadlines and ensure they are met. I help to coordinate internal processes such as linguistic review, and monitor the technical aspects of the process. As an ASM I am also involved in the acquisition of editors. 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1. Introduction
Low molecular mass organic compounds with internal charge transfer properties are widely adopted for organic photonics such as materials for the creation of molecular electronics elements, organic magnets, solar cells and organic light emitting diodes (OLEDs) for full display panels [1-3]. One of the most widely used red light-emitting materials contains pyranylidene (4H-pyran-4-ylidene) or isophorene (5,5-dimethylcyclohex-2-enylidene) fragments as backbone of the molecule (see Fig.1), which are conjugated in a system with electron acceptor and electron donor fragments [1,4-24]. In many cases the light-emitting layer from such commercially available compounds is prepared by thermal evaporation in vacuum [1-2, 25-27]. Some of them are used as dopants in a polymer matrix and spin-coated onto a hole transport layer from solution [1,12]. However the doping amount of luminescent compound is limited by self crystallization and photoluminescence quenching at higher concentrations which reduce the quantum efficiency of fabricated devices significantly [11-12]. Therefore it is important to synthesize low molecular mass light-emitting organic compounds which do not crystallize and form thin amorphous solid films from volatile organic solvents. Such compounds, which can make a solid-state glassy structure prepared from solutions, could facilitate technological processes in the production of many devices in optoelectronics, for example, light emitting devices by low-cost deposition such as wet casting methods and easier light-emitting material synthesis. Some of these red light-emitting compounds have been introduced by us [28-32].
In this chapter we present complete synthesis, thermal, optical, photoelectrical and glass forming properties of new organic glass-forming pyranylidene and isophorene fragment containing derivatives with bulky trityloxy groups in their molecules. The optical properties, both in solution and solid state, are compared. The dependance of photoelectrical properties and energy structure of glassy films on molecular structure will be discussed. The most popular derivatives of pyranylidene and isophorene used in OLEDs are shown in Fig.1.
Figure 1.
Most widely used pyranylidene and isophorene type red-emitters used as OLED emission layer materials
2. Synthesis
The synthesis procedure of pyranylidene and isophorene D-π-A type luminophores (see Fig.1) with either one or two electron donor fragments can be divided into three main parts:
Synthesis of a backbone fragment: Synthesis of derivatives of 4H-pyran-4-one, which in their molecules contain not only a carbonyl group, but also at least one methyl group and are able to react further with aromatic aldehydes.
Addition of an electron acceptor fragment to the backbone: Condensation reaction of 4H-pyran-4-one derivatives synthesized in 1) with active methylene group containing compounds.
Synthesis of pyranylidene and isophrene D-π-A type red emitters: Final addition of electron donor group containing aromatic aldehydes to compounds obtained in 2).
2.1. Synthesis of the backbone fragment: 2,6-disubstituted-4H-pyran-4-ones
The simplest of 2,6-disubstituted-4H-pyran-4-ones is 2,6-dimethyl-4H-pyran-4-one (compound 2 in Fig.2), which is obtained in 86% yield from dehydroacetic acid (compound 1 in Fig.2) by acidic rearrangement with following decarboxylation (see Fig.2) [32-33].
Figure 2.
Synthesis of 2,6-dimethyl-4H-pyran-4-one. Dehydroacetic acid (compound 1) is suspended either in concentrated hidrochloric acid (conc. HCl) or 10% aqueous sulfuric acid (10% H2SO4) and heated. During the heating carbon dioxide (CO2) is liberated and 2,6-dimethyl-4H-pyran-4-one (compound 2) is formed.
2,6-Dimethyl-4H-pyran-4-one (compound 2 in Fig.2) has one carbonyl group which can further react with active methylene group containing compounds in Knoevenagel condensation reactions. It also has two activated methyl groups, which can react in the same type of condensation reactions with one or two molecules of aromatic aldehydes.
Another method for the syntheis of 2,6-disubstituted-4H-pyran-4-ones, which contain at least one active methyl group, is using 4-hydroxy-6-methyl-2H-pyran-2-one (compound 3 in Fig.3) as starting material [11,34]. Its further reaction with isobutyryl chloride (compound 4 in Fig.3) in trifluoroacetic acid (TFA) gives 6-methyl-2-oxo-2H-pyran-4-yl isobutyrate (compound 5 in Fig.3). Without separating the compound 5 from the reaction mixture it was subjected to Fries rearrangement resulting in 4-hydroxy-3-isobutyryl-6-methyl-2H-pyran-2-one (compound 6 in Fig.3). In its decarboxylation and further acidic cyclization reactions 2-isopropyl-6-methyl-4H-pyran-4-one (compound 8 in Fig.3) is obtained with 80% yield. Compound 8 also contains a carbonyl group, just as the previously synthesized 2,6-dimethyl-4H-pyran-4-one (compound 2 in Fig.2). Since it now contains just one activated methyl group, only one aromatic aldehyde containing fragment can be added to the backbone of pyranylidene derivative 8 (shown in Fig.3).
One of the most preferred 2,6-disubstituted-4H-pyran-4-ones is 2-tert-butyl-6-methyl-4H-pyran-4-one (compound 13 in Fig.4) [7,11,35]. The first synthesis method starts from 3,3-dimethylbutan-2-one (compound 9 in Fig.4). Treating it with acetic anhydryde (Ac2O) and boron trifluoride (BF3) a boron enolate (compound 10 in Fig.4) is obtained. Its further condensation reaction with 1,1-dimethoxy-N,N-dimethylethanamine (compound 11 in Fig.4) produces N,N-dimethylamino-vinyl group containing boron enolate (compound 12 in Fig.4). Then following an acidic treatment gives 2-tert-butyl-6-methyl-4H-pyran-4-one (compound 13 in Fig.4). However this method has a drawback because two synthetic reactions towards our target compound had low yields (30-40%), which results in a very low overall yield for synthesis of 2-tert-butyl-6-methyl-4H-pyran-4-one (compound 13 in Fig.4).
Fortunately, there is another method for synthesizing 2-tert-butyl-6-methyl-4H-pyran-4-one (compound 13 in Fig.4) with good yields [7] using pentane-2,4-dione (compound 14 in Fig.5) as starting reactant.
In its Aldol reaction with methyl pivalate (compound 15 in Fig.5) a 7,7-dimethyloctane-2,4,6-trione (compound 16 in Fig.5) was formed. Without separating the compound 16 from reaction mixture it was subjected to acidic cyclization producing 2-tert-butyl-6-methyl-4H-pyran-4-one (compound 13 in Fig.5) with a good overall yield (60%). As with 2-isopropyl-6-methyl-4H-pyran-4-one (compound 8 in Fig.3), the resulting 2-tert-butyl-6-methyl-4H-pyran-4-one (compound 13 in Fig.5) also contains one carbonyl group and one activated methyl group with the possibility of also adding only one aromatic aldehyde containing fragment.
Figure 5.
Improved synthesis of 2-tert-butyl-6-methyl-4H-pyran-4-one (compound 13). NaH - sodium hydryde, conc. H2SO4 - concentrated sulfuric acid.
One of oldest, but no less important methods known for the synthesis of 2,6-disubstituted-4H-pyran-4-ones is to obtain them from 3-substituted-vinylcarbonyl-4-hydroxy-6-methyl-2H-pyran-2-ones (compounds 17 in Fig.6) [33]. Compounds 17 are obtained from dehydroacetic acid (compound 1 in Fig.6), in which the methyl group in the acetyl fragment is activated to react preferentially with aromatic aldehydes (see Fig.6) giving 3-substituted-vinylcarbonyl-4-hydroxy-6-methyl-2H-pyran-2-ones (compounds 17 in Fig.6) [33, 36]. Details on the obtained compounds 17 and their dependence on substituents (R) in their molecules are given in Table 1. They serve as precursors for further synthesis of pyranylidene type compounds.
Figure 6.
Synthesis of 3-substituted-vinylcarbonyl-4-hydroxy-6-methyl-2H-pyran-2-ones (Compounds 17). Above the arrow are different aromatic aldehydes with different substituents R (see Table 1), which all react with dehydroacetic acid (compound 1) the same way. CHCl3 - chloroform.
Using this approach it is possible to obtain many different mono-styryl-substituted 4H-pyran-4-ones (compounds 17 in Fig.7). However only a few of previously synthesized compounds 17 give 2-styryl-substituted-6-methyl-4H-pyran-4-ones (compounds 18 in Fig.7) by acidic decarboxylation under the reaction conditions reported in [30, 33] (see Fig.7) as summarised in Table 2.
R (of compounds 17)
Yield, %
M.p., °C
Recrystallized from
Phenyl
55
130-132
methanol
o-Nitrophenyl
65
161-163
acetic acid/water
m-Nitrophenyl
60
192
chloroform
p-Nitrophenyl
22
165-167
chloroform/ethyl acetate
p-Nitrophenyl
47
246-247
dioxane
p-Dimethylaminophenyl
71
198-200
Chloroform, ethyl acetate, benzene
p-Diethylaminophenyl
58
150
Chloroform, ethyl acetate
o-Hydroxyphenyl
67
186-188
methanol
m-Hydroxyphenyl
61
181-183
ethanol
p-Hydroxyphenyl
69
260-262
dioxane
p-Methoxyphenyl
73
153-154
ethanol
2,3-Dimethoxyphenyl
47
147
ethyl acetate
3,4-Dimetoxyphenyl
46
185
benzene/ethyl acetate
3,4-Diethoxyphenyl
43
163
ethyl acetate
o-Chlorophenyl
36
116-117
ethanol
p-Chlorophenyl
54
155-156
ethanol
3,4-Dichlorophenyl
46
185
ethyl acetate, benzene/chloroform
p-Isopropylphenyl
65
139-141
methanol
1-Naphtyl
62
190
ethyl acetate
β-styryl
57
185
chloroform/ethyl acetate
2-Furyl
85
144
benzene/ethyl acetate
Table 1.
Synthetic information on pyranylidene compounds 17 (see Fig.6).
Figure 7.
Synthesis of 2-styryl-substituted-6-methyl-4H-pyran-4-ones (compounds 18).
R (of compounds 18)
Yield, %
M.p., °C
Recrystallized from
p-Dimethylaminophenyl
82
156
ethyl acetale/petroleum ether
p-Diethylaminophenyl
68
128-130
methanol/water
o-Nitrophenyl
53
187-189
methanol/water
p-Isopropylphenyl
45
110-112
ethanol/water
Table 2.
Fries rearrangement possibility [33] of pyranylidene precursors 17 (Fig.7).
Some works can be found on red luminescent compounds where the pyranylidene fragment is hidden as a substructure in the molecule [8, 23-24]. For example, chromene type derivatives of pyranylidene are synthesized from 1-(2-hydroxyphenyl)ethanone (compound 19 in Fig.8) [23-24]. In the Claisen condensation reaction (see Fig.8) with ethyl-acetate in the presence of a strong base, 1-(2-hydroxyphenyl)butane-1,3-dione (compound 20 in Fig.8) is obtained. After separation it was subjected to acidic dehydrocyclization giving 2-methyl-4H-chromen-4-one (compound 21 in Fig.8) with an overall 45% yield.
Figure 8.
Synthesis of chromene fragment containing derivative of pyranylidene (compound 21).
For obtaining the benzopyran derivative of pyranylidene [8, 24], a two-stage synthesis procedure is started from 2-methylcyclohexanone (compound 22 in Fig.9).
Figure 9.
Synthesis of the benzopyran fragment containing derivative of pyranylidene (compounds 24).
In the first stage of synthesis, treatment with morpholine gives us enamine 23 (4-(6-methylcyclohex-1-enyl)morpholine). In the second stage of synthesis in reaction with 2,2,6-trimethyl-4H-1,3-dioxin-4-one, a 2,8-dimethyl-5,6,7,8-tetrahydro-4H-chromen-4-one (compound 24 in Fig.9) is sucessfully obtained. Once the desired pyranylidene compound is obtained, the addition of electron acceptor and electron donor fragments becomes a more simplified process, which will be described in detail below in this chapter.
2.2. Addition of electron acceptor fragments to derivatives of 4H-pyran-4-ones and 3,5,5-trimethylcyclohex-2-enone
The next step towards synthesizing fully functional pyranilydene and isophorene type red luminescent organic compounds is the addition of electron acceptor fragments to the previously obtained 2,6-disubstituted-4H-pyran-4-ones (see Fig.10) and 3,5,5-trimethylcyclohex-2-enone (see Fig.11).
Figure 10.
Synthesis of electron acceptor fragment containing derivatives of pyranylidene. Electron acceptors are marked in red while structure backbone, which serves as π-conjugated system remain in black.
Many different electron acceptor fragments (compounds 25-35 in Fig.10) can be introduced in 2,6-disubstituted-4H-pyran-4-ones [1,4-18, 28-30,32] using acetic anhydride (Ac2O) as solvent and catalyst. From these, malononitrile (compounds 25 in Fig.10) is the most commonly used. Since isophorene (3,5,5-trimethylcyclohex-2-enone) (compound 36 in Fig.11) is an inexpensive reagent, which can be purchased from chemical suppliers - such as ACROS and ALDRICH, all that remains is to add electron acceptor and electron donor fragments. As with 2,6-disubstituted-4H-pyran-4-ones, the electron acceptor fragments are added in Knoevenagel condensation reactions [18-21, 31, 37] with active methylene group containing compounds 37-39 (see Fig.11).
Figure 11.
Synthesis of electron acceptor fragment containing derivatives of isophorene (compounds 37-39). As in Figure 10, the electron acceptors are marked in red while the structure backbone remains in black.
The electron acceptor fragment containing derivatives of isophorene (3,5,5-trimethylcyclohex-2-enone) (compounds 37-39 in Fig.11) thus obtained are not always isolated from the reaction mixture [31, 37]. Once they are formed, the electron donor fragment containing aromatic aldehyde is added in the mixture for further reaction with the aldehyde.
2.3. Synthesis of pyranilydene and isophorene type red luminescent compounds by final addition of electron donor fragments
Once the electron acceptor fragment is introduced, the last step for obtaining a fully functional pyranylidene and isophorene red luminescent compounds is to add one or two electron donor fragment containing aldehydes. They are added in Knoevenagel condensation reactions with electron acceptor fragment containing derivatives of isophorene as shown in Fig.12 and pyranylidene shown in Fig.13, which contain one or two activated methyl groups.
For isophorene type compounds one electron donor fragment (40-44) is always introduced after an electron acceptor fragment is already in the molecule (see Fig.12) [18-21, 31, 37]. Many different structures of electron donor fragments are introduced (compounds 45-57 in Fig.13) in the pyranylidene backbone after introducing the electron acceptor fragment [1,4-18,27-29,31]. In cases where only one methyl group reacts with the aldehyde, a mono-styryl derivative of pyranylidene is obtained (see Fig.13). However, as all possible combinations shown in Fig.13 have not yet been synthesized, it presents a working opportunity for many organic chemists to contribute. If a pyranylidene type compound has two active methyl groups, like compound 25a, (see Fig.10) it will react with one or two aromatic aldehyde molecules producing chromophores 58-66 (see Fig.14). The reaction product will most likely be a mixture of mono- and bis- condensation products, which are difficult to separate and purify [32]. In reaction with two methyl groups bis-styryl derivatives of pyranylidene are obtained (see Fig.14).
Figure 12.
Synthesis of fully functional derivatives of isophorene (compounds 40-44). CH3CN - acetonitrile. Electron acceptor fragments are marked in red and electron donor fragments are marked in blue, while the backbone structure fragments remain in black and serve as a π-conjugated system.
A good summary on dicyanomethylene-pyranylidene type red-emitters has been made by Guo et al. [24], according to which the mono electron donor fragment containing pyranylidene-type materials (45a-c to 57a-c in Fig.13) usually have high luminescence quantum yield but their chromaticity is not sufficiently good. At the same time two electron donor fragment derivatives of pyranylidene (compounds 58-66 in Fig.14) have better chromaticity, but their luminance efficiency is relatively low, particulary those with larger conjugations leading to a broad light-emission peak above 650 nm extending to the NIR region, which decreases the efficiency of red electroluminescent materials.
Both chromene (compounds 47,49-50 in Fig.13) and benzopyran (compounds 47,49,51 in Fig.13) type derivatives of pyranylidene have only one electron donor fragment in their molecules, but their optical properties are different. Since chromene type derivatives of pyranylidene have an additional conjugated aromatic ring in its molecule, its optical properties are similar to those with two electron donor fragment derivatives of pyranylidene (compounds 58-66 in Fig.14). At the same time benzopyran pyranylidene compounds 45,46,49 have a simple cyclohexene ring without additional conjugation, so their optical properties are more similar to pyranylidene-type red-emitters, compounds 45a-c to 57a-c.
Figure 13.
Synthesis of fully functional mono-styryl substituted derivatives of pyranylidene. Electron acceptors are marked in red, electron donors is blue and structure backbone remains in black.
If a pyranylidene backbone with different electron acceptor fragments contains two active methyl groups, then in reaction with a two aldehyde group containing compounds a polymer is formed during the reaction (see Fig.15) [38]. The resulting polymers 70-72 are also reported to be red light-emitting materials.
All derivatives of pyranylidene and isophorene reported so far in this chapter are deposited on the OLED hole transport layer either by thermal evaporation in vacuum or used as dopants in a polymer matrix in limited concentrations.
Figure 14.
Synthesis of fully functional di-styryl substituted derivatives of pyranylidene. Color significance is the same as for previous figures.
Figure 15.
Synthesis of polymeric derivatives of pyranylidene. Color significance is the same as for previous figures.
3. Synthesis and properties of trityloxy group containing glassy derivatives of pyranylidene and isophorene
Our key for obtaining glass forming materials is the synthesis of such electron donor substituent containing aldehyde which would ensure the formation of an amorphous structure of our newly synthesized derivatives of pyranylidene and isophorene. We have synthesized such a compound - 4-(bis(2-(trityloxy)ethyl)amino) benzaldehyde [31-32] 75, in Fig.16.
3.1. Preparation of molecular glasses
For obtaining a red luminescent glass forming derivative of isophorene, we start with (3,5,5-trimethylcyclohex-2-enone) (compound 29 in Fig.16) as already described in Fig.9. It is subjected to the Knoevenagel condensation reaction with malononitrile (28). However, 2-(3,5,5-trimethylcyclohex-2-enylidene)malononitrile (61) which is formed during the reaction is not isolated because 4-(bis(2-(trityloxy)ethyl)amino) benzaldehyde (75) is added to the reaction mixture after 2 hours [31, 37] for further reaction. 2-(3-(4-(Bis(2-(trityloxy)ethyl)amino)styryl)-5,5-dimethylcyclohex-2-enylidene)malononitrile (IWK) was obtained in good yield after its separation and purification by liyquid column chromatography as described in [31].
Figure 16.
One pot" synthesis of IWK. (See previous figures for explanation of color significance).
For obtaining red luminescent glass forming derivatives of pyranylidene, we use three different electron acceptor fragment containing derivatives of pyranylidene (compounds 25a in Fig.17). Malononitrile (in compounds 74a and 75a), indene-1,3-dione (in compounds 74b and 75b) and barbituric acid (in compounds 74c and 75c) are used as electron acceptor fragment carrying compounds [32].
In the Knoevenagel condensation reaction with compound 25a and 4-(bis(2-(trityloxy)ethyl)amino) benzaldehyde (73) a mixture of mono- (ZWK-1, DWK-1, JWK-1) and bis- (ZWK-2, DWK-2, JWK-2) condensation products is obtained. Their separation is complicated but nevertheless a large part of each product was separated by liquid column chromatography (silicagel and dichloromethane for ZWK-1 and ZWK-2, dichloromethane: hexane = 4:1 for DWK-1 and DWK-2, dichloromethane: ethyl acetate = 4:1 for JWK-1 and JWK-2). The physical properties of compounds WK-1, WK-2 and IWK are described in detail further in this chapter.
Figure 17.
Synthesis of glass forming derivatives of pyranylidene. Py - pyridine. (See previous figures for explanation of color significance). Since compounds 74a-c and 75a-c are our obtained red light-emitting materials, we have assigned specific names for each (ZWK-1, ZWK-2, DWK-1, DWK-2, JWK-1 and JWK-2) [28-30, 32, 46].
3.2. Thermal properties
The thermogravimetric analysis (TGA) of trityl group containing pyranylidene type compounds is used to measure their thermal decomposition temperatures (Td). Td of compounds WK-1 and WK-2 are determined in the temperature range from +30°C to +510°C at a heating rate of 10°C/min [32] at the level of 10% weight loss (see Fig.18).
Pyranylidene type compounds with two N,N-ditrityloxyethylamino electron donor fragments (ZWK-2, DWK-2, JWK-2) are slightly more thermally stable than compounds containing only one such fragment, i.e. ZWK-1, DWK-1 or JWK-1. The increase in thermal stability of pyranylidene type compounds by adding another electron donor fragment is as high as 10°C from ZWK-1 to ZWK-2, 19°C from JWK-1 to JWK-2 and 29°C from DWK-1 to DWK-2. The most thermally stable compound is a two electron donor fragment containing derivative of pyranylidene with malononitrile as electron acceptor in it (DWK-2).
Differential scanning calorimetry (DSC) measurements are used to measure the glass transition temperatures (Tg) of the compounds WK-1 and WK-2. Three thermo cycles are performed for the determination of Tg. The first scan was done within the temperature range
Figure 18.
Thermogravimetric analysis of compounds WK-1 and WK-2. A sample of each compound is constantly weighed during heating. At some temperature (Td) the mass of the sample starts to decrease rapidly - this indicates when the respective compound starts to decompose and is no longer thermally stable.
from +25°C to +250°C at a heating rate of 10°C/min [32]. After the first heating scan samples of the compounds were cooled to 25°C at a rate of 50°C/min and heated for a second time from +25°C to +250°C at a rate of 10°C/min. The Tg value is obtained from the second heating scan (see Fig.19) and for almost all compounds is higher than 100°C. We could not obtain usable DSC curves for DWK-1. The compounds with two N,N-ditrityloxyethylamino electron donor fragments have higher Tg compared to those with only one electron donor fragment, which may be attributed to the different numbers of bulky trityloxyethyl groups attached to the two electron donor fragment. In a larger number of bulky groups Tg increases by 8°C from ZWK-1 to ZWK-2 and 7°C from JWK-1 to JWK-2. Pyranylidene type compounds with barbituric acid as electron acceptor, e.g. JWK-1 and JWK-2 have the highest Tg values compared to ZWK-1, ZWK-2 and DWK-2, which may be due to the additional formation of intermolecular hydrogen bonds by N-H groups of barbituric acid fragments in the molecules.
Figure 19.
DSC thermogramms of compounds WK-1 and WK-2. Since amorphous compounds have several solid state phase modifications, the glass transition temperature (Tg) indicates when compound solid structure transitions from a more kinetically stable phase (with more free volume) to a more thermodynamically stable phase (with less free volume). During such phase transitions some ammount of heat is absorbed (endothermic process) which appears as a small drop on the DSC curves.
The TGA analysis of IWK is conducted as previously described [32]. The thermal decomposition temperature (Td) of IWK is found to be even higher than that of pyranylidene type compounds WK-1 and WK-2 (see Fig.20). However its glass transition temperature (Tg) is lower by 18°C to 35°C degrees compared to that of pyranylidene type glasses. Despite the lower thermal stability, the pyranylidene type compounds WK-1 and WK-2 have better glass forming properties than the isophorene type compound IWK.
Figure 20.
TGA and DSC analysis of IWK. (Please see Fig.18 and Fig.19 for a more detailed explanation).
3.3. Glass forming properties
Thin films are deposited on quartz glass by the spin-coating technique. Before the deposition of the layers, the quartz glass substrates are cleaned in dichloromethane. The solutions are spin-coated onto the substrates for 40 s at 400 rpm and acceleration 200 rpm/s.
In all cases, pure films obtained from two electron donor fragment containing pyranylidene compounds (ZWK-2, DWK-2 and JWK-2) have an almost pure smooth and amorphous surface, but pyranylidene compounds with one electron donor fragment (ZWK-1, DWK-1 and JWK-1) show several crystalline state areas (see Fig.21). Both glasses containing barbituric acid as an electron acceptor fragment (JWK-1 and JWK-2) show the least amount of small crystal formations on their pure film surface. The higher stability of their amorphous state could be explained by an enchancement of N-H group hydrogen bonds in the molecules. Pure films obtained from malononitrile electron acceptor fragment containing compounds (DWK-1 and DWK-2) contain small crystal dots, especially DWK-1. This could be due to small steric dimensions of malononitrile group, which allows more DWK-1 molecules to be concentrated in the same volume to allow closer interaction with other molecules enabling higher possibility to form agreggates and crystallites.
Information obtained from the surfaces of the pure films is consistent with the measured glass transition temperatures (Tg). Glasses having higher Tg values are found to have less crystalline dots on their pure film surface. As we were unable to determinate Tg for DWK-1, according to above mentioned trend its glass transition temperature is expected to be below 110°C.
Thin film containing only pyranylidene type compound WK-1 and WK-2 are amourphous despite of small crystalline dots in it. Till now only way to prepare amourphse films which contain pyranyliden derivatives was doping them in glass forming compound. In that case maximum doping concentration was considered to be 2wt% due to self crystallization [11-12]. However, incorporation of bulky trityloxy groups in their molecules or using glasses WK-1 and WK-2 could increase this concentration limit more then 10 times.
Figure 21.
Optical mircroscope images of the pure films of the compound WK-1 and WK-2. Dots on the pure film surface represent compound crystalline state while the remaining smooth area shows amorphous solid state.
3.4. Absorption and luminescence properties
The absorption and fluorescence spectra of the synthesized compounds in diluted dichloromethane solution and pure films are shown in Figs. 22 and 23.
A DWK-1 molecule, whose backbone consists of the laser dye 4-(dicyanomethylene)-2-methyl-6-[p-(dimethylamino)styryl]-4H-pyran (DCM), in dichloromethane solution has its absorption maximum at 472 nm, which is 8 nm red shifted with respect to the pure DCM molecule in the same solution [9]. It shows that the bulky trityloxyethyl group has only a small influence on the energy structure of the molecule. The peaks of the absorption spectra in solution of the molecules with indene-1,3-dione (ZWK-1) and barbituric acid (JWK-1) electron acceptor substituents in the backbone are red-shifted by approximately 40 nm compared to DWK-1. A stronger electron acceptor group gives larger red shifts.
Figure 22.
Absorption and 2) Photoluminescence spectra of compounds WK-1 and WK-2 in dichloromethane solution
Figure 23.
Absorption and 2) Photoluminescence spectra of compounds WK-1 and WK-2 in thin solid films
The photoluminescence (PL) spectrum of the DWK-1 solution was found to be Stokes shifted by about 115 nm (peak position at 587 nm) with respect to the absorption spectra (see Fig.22). The PL spectra of JWK-1 and ZWK-1 molecules exhibited similar shapes, with their maxima red-shifted to 635 and 627 nm, respectively. The photoluminescence spectra are unstructured and strongly Stokes shifted in accordance with intramolecular charge-transfer nature of the excited states [39]. For compounds containing two 4-((N,N-ditrityloxyethyl) amino)styryl electron donor fragments the absorption and luminescence spectra of the solution are observed to be red-shifted and have larger extinction coefficients, which is due to the larger absorption cross section of these molecules. The peaks of the absorption spectra of DWK-2 and ZWK-2 are red shifted by 17 and 11 nm, respectively, compared to molecules with a single electron donor fragment. A similar red shift has been reported for the molecule with two electron donor fragments bis-DCM compared with DCM molecules with a single electron donor fragment [40]. It is observed that molecules with two electron donor fragments have a larger conjugation length. A second reason could be simultaneously functioning two donor groups which give stronger electron donor properties. The shape of the absorption spectrum of JWK-2 is found to be different from that of JWK-1 and the oscillator strength of the absorption band of JWK-2 at about 502 nm becomes more intense (see Fig.22(1)).
The fluorescence spectra of molecules with two electron donor fragments are broader and further Stokes shifted than molecules with only one electron donor fragment. This may be attributed to the different conjugation lengths as indicated by the absorption spectra. The peak positions of DWK-2, ZWK-2 and JWK-2 are observed at 640, 678 and 701 nm, respectively. The red shift of the absorption spectra of solutions increases corresponding sequentially to ZWK, JWK and DWK, as stronger electron acceptor fragments induce larger red shifts. This could be explained by their electron withdrawing properties, which differ among our investigated electron acceptor fragments. The shift of luminescence spectra did not maintain the same sequence due to the larger Stokes shift for the JWK molecules.
The absorption spectra of thin solid films of the molecules with one electron donor fragments are practically unchanged with respect to the solutions spectra. They are slightly broader with small red-shift indicating a weak excitonic interaction in the solid state, which is typical for glass-forming amorphous materials. For the molecules with two electron donor fragments ZWK and DWK the absorption spectra are found to shift by 21 nm and 22 nm, respectively. The peak positions of the absorption spectra for JWK molecules remain unchanged by the incorporation of a second electron donor fragment. However, the fluorescence spectra of all films are red-shifted in comparison with those of solution.
For molecules with one electron donor fragment, the shape of the fluorescence spectra of thin films is very similar to that in solution, which confirms that for these compounds the excited states in the aggregates in the solid state are not very different from those in molecules. However, the derivatives with two electron donor fragments exhibit an additional band at longer wavelengths in thin films, which becomes more intense going from weaker to stronger electron acceptor fragments in the studied molecules. In the case of ZWK-2 in thin films the additional band even becomes dominant.
In the case of IWK, the absorption and luminescence spectra of thin solid films are also found to be practically unchanged compared to its solutions spectra as shown in Fig.24.
Figure 24.
Absorption and 2) Emission of IWK in solutions and thin solid film
The same relation is observed for IWK emission properties in solution as well as in thin films. However, in solid state its emission is very weak compared to pyranylidene type compounds, which may limit the usefulness of IWK in OLED applications.
3.5. Photoluminescence quantum yields
Photoluminescence quantum yield (PLQY) of the investigated compounds in solution and in thin films is measured by using an integrating sphere (Sphere Optics) coupled to a CCD spectrometer [41]. PLQY thus measured for all compounds are summarised in Table 3. Compounds with more polar groups attached exhibit PLQY up to 0.54 in dilute solutions, which is slightly higher than for DCM dye in similar surroundings [42, 43]. PLQY depends slightly on the acceptor group as can be seen from Table 3. That means that compounds with a stronger electron acceptor group have higher PLQY. JWK and ZWK molecules with two electron donor groups have lower PLQY in comparison with one electron donor group. However, the opposite is observed with DWK compounds, as molecules with two electron donor groups exhibit larger PLQY. This may be due to the shielding of the acceptor group by bulky trityloxyethyl groups. PLQY of pure films is found to be more than one order of magnitude lower than that in solution. This reduction is particularly strong in the case of molecules with two donor groups. PLQY values of these compounds correlate with the intensity of the long wavelength fluorescence band, as PLQY is lower in materials with a stronger low energy fluorescence band. Molecular distortions taking place during formation of solid films are probably responsible for both of these effects. Compound molecules with two bulky acceptor groups are probably strongly distorted in solid films, so that molecular chains connecting acceptor and donor moieties are twisted. Such twisting usually leads to a red-shift in the molecular fluorescence and to fast non-radiative relaxation [44]. The twisted molecules form energy traps in solid films, which may be populated during the excitation diffusion. Therefore, even a small fraction of distorted molecules may significantly affect the fluorescence spectrum and PLQY. We were unable to measure PLQY in IWK pure thin solid films. Moreover, it also shows the lowest value in solution and therefore cannot be used as a light-emitting material.
Solution
Thin film
DWK-1
0.32
0.026
DWK-2
0.43
0.009
JWK-1
0.47
0.011
JWK-2
0.32
0.007
ZWK-1
0.54
0.01
ZWK-2
0.4
0.003
IWK
0.098
-
Table 3.
Photoluminescence quantum yield of investigated molecules in dichlormethane solutions and pure thin films.
It is worth mentioning that DCM molecules do not show any photoluminescence from pure films due to the small distance between molecules which results in high molecular interaction. Therefore, host-guest films of transparent polymethylmethacrylat (PMMA) polymer with varying dye doping were prepared in order to observe the impact of concentration on photoluminescence quenching. The dependence of PLQY on concentration of DWK-1 and DWK-2 molecules is shown in Fig.25.
Figure 25.
The dependence of PLQY on concentration of DWK-1, DWK-2 and DCM dyes in PMMA matrix.
For comparison the PLQY of DCM in PMMA are also included in Fig.25. PMMA films doped with DWK-1 and DWK-2 at low concentration (<1 wt%) exhibit somewhat lower PLQY as compared to that obtained in solution (See Fig.24 and Table 3). This discrepancy may be attributed to the sensitivity of molecules to the polarity of the surrounding media. At higher concentrations (>3 wt%) the DWK-1 molecule shows negligible photoluminescence quenching dependence on concentration. On the other hand molecules with two donor groups exhibit pronounced quenching. Fluorescence efficiency of the polymer film doped with 10 wt% of DWK-2 molecules decreases 2-times compared to that of films doped with 10 wt% DWK-1 molecules. The reason for the lower PLQY could be the same as for different PLQY of the pure films. The laser dye DCM dispersed in the polymer matrix at high concentration shows a remarkable fluorescence quenching. For example, at a 10 wt% concentration of DCM molecules, up to a 4-time decrease of quantum yield is observed in comparison with the same concentration of DWK-1 molecules. Thus, incorporation of bulky trityloxyethyl groups prevents the formation of aggregates of the dye molecules and remarkably reduces the fluorescence quenching dependence on concentration, enabling the use of higher doping levels in emissive layers.
3.6. Amplified spontaneous emission properties
DCM molecule is a well known laser dye. In a previous work light amplification was demonstrated in DCM:Alq3 (see Fig.25 and Fig.26) thin films [45].
Figure 26.
Tris(8-hydroxyquinolinato)aluminium (Alq3) is a well known light-emitting material.
In order to test the light amplification prospects of our synthesized compounds, we prepared pure thin films of all the compounds on a quartz substrate and measured their amplified spontaneous emission (ASE). Such emission was observed only for four of six compounds, DWK-1, DWK-2, JWK-1 and ZWK-1, as shown in Fig.27 [46].
Figure 27.
ASE spectrum in pure films of compounds ZWK-1, DWK-1, DWK-2 and JWK-1
From the other two samples of JWK-2 and ZWK-2 no ASE signal has been observed. The peak positions of ASE are red shifted as compared to the fluorescence band maxima (see Fig.27 and Fig.22). The red shift values were found to be 14, 18, 10 and 31 nm for DWK-1, DWK-2, JWK-1 and ZWK-1, respectively. Variations in the peak intensity of ASE spectra as a function of the pump beam pulse energy are shown in Fig.28, from which ASE threshold values are estimated to be 90±10, 330±20, 95±10, 225±20 μJ/cm2 for DWK-1, DWK-2, JWK-1 and ZWK-1, respectively. These values are larger in comparison with the threshold values (of the order of micro joules per square centimeter) reported for some other materials [46, 47].
However, a direct comparison is difficult because the ASE threshold, in addition to material properties, depends also on the sample and excitation geometries, film thickness, optical quality and excitation pulse duration.
Nevertheless it has not been observe ASE in pure DCM films, but we have measured it in DWK-1 which is the same DCM with additional trityloxyethyl group. It should also be noted that some sample degradation has been observed at the highest excitation intensities; however no noticeable degradation is observed when excitation intensity is 1.5 - 2 times exceeding the ASE threshold.
Figure 28.
ASE intensity as a function of irradiation pulse energy in DWK-1, DWK-2, JWK-1, ZWK-1 compounds in thin solid film. Lines are guides for the eye.
ASE develops in the spectral position where the light amplification coefficient has the maximal value. The amplification coefficient may be described as:
a(λ)=n*[(σem(λ)−σ*(λ)]−(N−n*)σ0(λ)E1
where n* is the density of excited molecules, N is the total density of molecules, σ0(λ),σem(λ)and σ*(λ) are cross-sections of the ground state absorption, stimulated emission and excited state absorption, respectively. As it can be seen from Eq. (1) even weak ground state absorption may strongly reduce the amplification coefficient or make it negative. This is because only a small fraction of molecules is usually excited even under high intensity excitation conditions, i.e., N>>n*. Thus, the absorption band tails, which overlap with fluorescence band, are evidently responsible for the red shifts in ASE spectra in comparison with the maxima of the fluorescence. Note, that the light propagation length is limited by the film thickness in the absorption measurements, while ASE emission can propagate a much longer way along the film.
3.7. Photoelectrical properties and energy structure of glassy thin films
Information about the location of energy levels enables one to determine the best sample structure for electroluminescence measurements. To characterize the energy gap in organic solids several methods are applied. In organic crystals as well as amorphous solids charge carriers do not emerge as “bare” quasi-free electrons and holes but as a polaron type quasi-particle, dressed “in electronic and vibronic polarization clouds” [48, 49]. Electronically relaxed charges may be formed far enough from each other which give rise to a wider optical band gap EGOpt [49, 50]. The optical energy gap EGOpt may be obtained from the low energy threshold of the absorption spectra of organic thin films. The vibrationally and electronically relaxed charge carrier states contribute to the adiabatic energy gap EGAd. It could be attributed to the threshold energy of photoconductivity Eth which can be estimated from the spectrum of the quantum efficiency of photoconductivity β(hυ) [49]:
β(hν,U)=jph(hν,U)k(hν)I(hν)g(hν)E2
where jph is the density of photocurrent at a given photon energy hν and applied voltage U, I(hν) is the intensity of light (photons/cm2s), k(hν) is the transmittance of the semitransparent electrode and g(hν) is the coefficient which characterizes the absorbed light in the organic layer.
Eth can be determined from a sample where the organic compound is sandwiched between two semitransparent electrodes, which in our case are ITO and thermally evaporated aluminum. The sample is irradiated through the electrodes and current changes are measured as shown in Fig.29(1). Efficiency of photoconductivity at different light energy is calculated using Eq. (2) and is plotted as a function of the photon energy in Fig.29(2). The sample is illuminated from both aluminum and ITO side when positive and negative voltage is applied to them. Eth is determined by plotting β2/5 as a function of the photon energy. The intersections of tangents at low photon energy on the curve of β2/5 plotted as a function of the photon energy and photon energy axis gives Eth as shown in Fig.29(3).
Figure 29.
Photocurrent at different wavelength for JWK-2 compound,2) Dependency of photoconductivity efficiency on photon energy for JWK-2 compound,3) Determination of Eth from photoconductivity efficiency spectral dependence.
Optical band gap EGOpt, photoconductivity threshold value Eth and reduction-oxidation potential Uredox, determined from cyclic voltamperogramme, for investigated compounds are presented in Table 4.
EGOpt (eV)
Eth (eV)
Uredox (V)
DWK-1
2.20
1.92
2.35
DWK-2
2.10
-
1.99
JWK-1
2.08
1.78
2.01
JWK-2
1.88
1.62
1.90
ZWK-1
2.08
1.78
2.04
ZWK-2
1.96
1.68
2.00
Table 4.
Optical band gap EGOpt, photoconductivity threshold value Eth and red-ox potential Uredox for the compunds DWK-1, DWK-2, JWK-1, JWK-2, ZWK-1, ZWK-2.
According to Table 4, the redox potential of DWK, JWK and ZWK is higher for compounds with one electron donor group compared to compounds with two electron donor groups (see Fig.17). The same relation is found for optical band gap as well.
The photoconductivity threshold value cannot be obtained for DWK-2 thin films due to the low value of photocurrent. For other compounds we obtain an excellent linear correlation between optical band gaps and photoconductivity threshold values with correlation coefficient 0.993. The slope of this linear relation is found to be 1 and intercept 0.28 as shown in Fig.31
Figure 30.
Cyclic voltamperogramme curves of compounds WK-1 and WK-2. Posistive values are oxidation potential and negative values reduction potential.
Figure 31.
Linear correlation between optical band gap and photoconductivity threshold value. Line is the best fit with slope coefficient one.
The energy of the photoconductivity threshold is defined as the difference between the conduction levels of holes and electrons [51]. The value of the intercept implies that the optical band gap is 0.28 eV larger than the difference between the conduction levels of holes and electrons. It shows a constant energy difference between optical band gap and adiabatic gap despite the various molecule structures.
3.8. Electrical properties
Electrical properties of WK-1 and WK-2 compounds are investigated in the regime of space charge limited current (SCLC) [52-54]. Similar sandwich type samples as used for photoelectrical measurements are prepared for this study as well. The thickness of the organic thin film is at least 500 nm.
The current-voltage characteristics of compounds ZWK-1, ZWK-2, JWK-1, JWK-2 and DWK-2 in thin solid films are shown in Fig.32.
The current-voltage characteristic of DWK-1 films could not be measured due to unstable current. This may be due to formation of small crystallites (see Fig.21) around 1 μm in size. Such aggregates are found throughout the sample and induce instability in the current. In all other cases the current-voltage characteristics have similar shapes with three regions. In the first region, 0-2 volts, the current is found to depend linearly on voltage. In the second range, 2 to 50 volts the current increases superlinearly with voltage, following Child’s law. In the third region, > 50 V, the current depends on voltage to the power of at least ten, which may be attributable to charge trapping in the local trap states. More details of this aspect will be discussed further below.
Usually the work function of ITO should be near the ionisation energy level of the organic compound while that of aluminium (Al) should be around the middle of the energy gap. This provides efficient hole injection from ITO and electron injection from aluminium when a positive voltage is applied to ITO. Holes may also be injected from the aluminium when positive voltage applied to it. Electron injection may be more difficult in the second case due to the large difference between the ITO work function and electron affinity potential of the organic compound. This is confirmed by the current voltage characteristics shown in Fig.32. A similar current is observed at the lower voltage where only holes are injected either from ITO or aluminium when biased with a positive voltage. At higher voltage current is higher when ITO is positive in comparison with positive aluminium.
Figure 32.
Current-voltage characteristics of pure thin films of ZWK, JWK, DWK compounds. Solid line – compounds with one electron donor group, dashed line - compounds with two electron donor group.
The temperature modulated space charge limit current (TM SCLC) method is used to analyse the charge carrier local trapping states in solid films [55]. The condition for using this method (TM SCLC) is monopolar injection, which is achieved in our case when a positive voltage is applied to the aluminium electrode. The measured activation energy is plotted as a function of the applied voltage for the investigated compounds as shown in Fig.33.
No charge carrier local trap states are found in films of compounds with one electron donor group due to only one plateau which reaches zero. All compounds with two electron donor groups are found to have charge carrier trap states. The additional plateau of activation energy, which can be clearly seen from Fig.33 means that the thin films contain local trap states. The hole shallow trap depths are found to be 0.1, 0.24 and 0.3 eV in ZWK-2\n\t\t\t\t\tJWK-2 and DWK-2, respectively. Such trap states decrease the efficiency of electroluminescence and should be avoided in fabricating high efficiency light emitting diodes. The activation energy increases at lower voltage for compounds JWK-1, JWK-2 and DWK-2. This is indicative of a contact problem where the electrode – organic interface also works as additional charge carrier traps.
Figure 33.
Activation energy dependence on applied voltage of the investigated compounds in solid films. Positive voltage was applied to aluminium electrode.
3.9. Electroluminescence of ZWK-1 and ZWK-2
A multilayer structure is used for electroluminescence (EL) measurements. Polyethylenedioxythiophenne:polystyrenesulfonate (PEDOT:PSS) (from H.C. Starck) is used as the hole injection layer and LiF as electron injection layer. PEDOT:PSS and organic compounds are sequentially spin coated on ITO glass. Then LiF and Al are thermally evaporated in vacuum. The final structure of the device has a structure of ITO/PEDOT:PSS(40nm)/ZWK1 or ZWK-2(~90nm)/LiF(1nm)/Al(100nm) and is not encapsulated.
The EL spectrum of the device is estimated in International Commission on Illumination (CIE) coordinates: x=0.65 and y=0.34 for ZWK-1 and x=0.64 and y=0.36 for ZWK-2. The spectral maximum peak is observed at 667 nm and 705 nm in ZWK-1 and ZWK-2, respectively, as shown in Fig.34. These peaks are slightly red shifted compared with those of PL spectrum of ZWK-1 and ZWK-2 thin films. This red shift may be attributed to the interaction of molecules and injected charges.
Figure 34.
a) Electroluminescence spectrum and b) light intensity dependence on voltage of ZWK-1 (line) and ZWK-2 compounds (doted line)
The light emission is observed at 6 V in the electroluminescent device with ZWK-1 molecules and 9 V in with ZWK-2 molecules. The light intensity is one order less in ZWK-2 molecules compared to that in ZWK-1. This may be due to the lower PLQY and shallow charge carrier trap states in ZWK-2.
4. Conclusions
The absorption and emission bands of the synthesized pyranylidene type compounds ZWK-1, DWK-1, JWK-1 are comparable with those of other already known one electron donor fragment DCM and benzopyran type derivatives of pyranylidene within the spectral region studied here. Similar conclusions can be drawn about ZWK-2, DWK-2, JWK-2, which have similar properties to IWK and two other already known electron donnor group containing derivatives of pyranylidene. These properties are also similar to those of one electron donor fragment chromene red-emitters. However, incorporation of bulky trityloxy groups in such molecules not only enchances glass transition temperatures by 5° to 20°C compared to previously published pyranylidene type compounds containing one and two electron donor groups, but also enables the formation of a glassy structure in the solid state from volatile organic solvents. In addition, no glass transition values have been observed so far for low molecular mass isophorene type compounds. The photoluminescence quantum yield of investigated molecules in solution is up to 0.54 and is also comparable with the quantum yield of pyranylidene and isophorene derivatives already reported. Most of the thin solid films obtained from WK-1, WK-2 have almost no crystals in the sample. Newertheless the photoluminescence quantum yield is reduced by one order of magnitude due to the closer intermolecular distance between molecules, resulting in strong excitonic interaction. Emission from the IWK film is too weak to detect, which may be attributed to the higher photoluminescence quenching in IWK than in glassy pyranylidene films. However, using the doping approach, the compounds we have introduced enable up to 3 times higher doping concentration without losing optical properties compared to other already known red-emitters.
Four investigated compounds - ZWK-1, JWK-2, DWK-1 and DWK-2 show amplified spontaneous emission from pure solid films. Obtained threshold values are larger than those previously reported, but it should be mentioned that for pyranylidene type compounds, amplified spontaneous emission has been observed only in the doped systems until now.
Electrical properties are found to be better in compounds with one electron donor group due to absence of local trap states in their thin films. In the case of molecules with two electron donor groups shallow hole trap states have been observed, which may decrease efficiency of electroluminescence and should therefore be avoided in fabricating high efficiency light emitting diodes.
Even though we are able to prevent pyranylidene and isophorene type red-emitters from self crystallization in the solid state, their concentration in the emission layer would still be limited due to photoluminescence quenching caused by the short distance between molecules. Nevertheless, the glass materials can still be used not only as dopants for OLED applications, but also for lasing applications. Good thermal properties present a possibility of using them also for nonlinear optical (NLO) property studies.
Acknowledgement
This work has been supported by the European Social Fund within the project «Support for the implementation of doctoral studies at Riga Technical University» and «Support for Doctoral Studies at University of Latvia» and by Latvian State Research Programm No.2 in Materials Sciences and Information Technologies. Authors are grateful to Janis Jubles for assistance on reactant synthesis, Kristine Lazdovica for absorption and emission measurements in solutions and conducting thermogravimetric analysis, Dr. chem. Baiba Turofska for electrochemical measurements, Kaspars Pudzs for activation energy measurements, Raitis Grzibovskis for photoelectrical measurements, Dr. phys. Saulius Jursenas for photoluminescence quantum yield measurements, Dr. phys. Vidmantas Gulbinas for useful discussion and Dr. phys. Mikelis Svilans for providing language help.
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Introduction",level:"1"},{id:"sec_2",title:"2. Synthesis ",level:"1"},{id:"sec_2_2",title:"2.1. Synthesis of the backbone fragment: 2,6-disubstituted-4H-pyran-4-ones",level:"2"},{id:"sec_3_2",title:"2.2. Addition of electron acceptor fragments to derivatives of 4H-pyran-4-ones and 3,5,5-trimethylcyclohex-2-enone",level:"2"},{id:"sec_4_2",title:"2.3. Synthesis of pyranilydene and isophorene type red luminescent compounds by final addition of electron donor fragments",level:"2"},{id:"sec_6",title:"3. Synthesis and properties of trityloxy group containing glassy derivatives of pyranylidene and isophorene ",level:"1"},{id:"sec_6_2",title:"3.1. Preparation of molecular glasses",level:"2"},{id:"sec_7_2",title:"3.2. Thermal properties",level:"2"},{id:"sec_8_2",title:"3.3. Glass forming properties",level:"2"},{id:"sec_9_2",title:"3.4. Absorption and luminescence properties",level:"2"},{id:"sec_10_2",title:"3.5. Photoluminescence quantum yields",level:"2"},{id:"sec_11_2",title:"3.6. 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Maxwell, Pavel Klang, Werner Schrenk and Gottfried Strasser",authors:[{id:"4537",title:"DI",name:"Alexander",middleName:null,surname:"Benz",fullName:"Alexander Benz",slug:"alexander-benz"},{id:"135394",title:"Prof.",name:"Christoph",middleName:null,surname:"Deutsch",fullName:"Christoph Deutsch",slug:"christoph-deutsch"},{id:"135395",title:"Prof.",name:"Gernot",middleName:null,surname:"Fasching",fullName:"Gernot Fasching",slug:"gernot-fasching"},{id:"135396",title:"Prof.",name:"Karl",middleName:null,surname:"Unterrainer",fullName:"Karl Unterrainer",slug:"karl-unterrainer"},{id:"135397",title:"Prof.",name:"Aaron",middleName:null,surname:"Maxwell",fullName:"Aaron Maxwell",slug:"aaron-maxwell"},{id:"135398",title:"Prof.",name:"Pavel",middleName:null,surname:"Klang",fullName:"Pavel Klang",slug:"pavel-klang"},{id:"135399",title:"Prof.",name:"Werner",middleName:null,surname:"Schrenk",fullName:"Werner Schrenk",slug:"werner-schrenk"},{id:"135400",title:"Prof.",name:"Gottfried",middleName:null,surname:"Strasser",fullName:"Gottfried Strasser",slug:"gottfried-strasser"}]},{id:"8448",title:"High-Power and High Efficiency Yb:YAG Ceramic Laser at Room Temperature",slug:"high-power-and-high-efficiency-yb-yag-ceramic-laser-at-room-temperature",signatures:"Shinki Nakamura",authors:[{id:"4143",title:"Dr.",name:"Shinki",middleName:null,surname:"Nakamura",fullName:"Shinki Nakamura",slug:"shinki-nakamura"}]},{id:"8449",title:"Polarization Properties of Laser-Diode-Pumped Microchip Nd:YAG Ceramic Lasers",slug:"polarization-properties-of-laser-diode-pumped-microchip-nd-yag-ceramic-lasers",signatures:"Kenju Otsuka",authors:[{id:"4259",title:"Professor",name:"Kenju",middleName:null,surname:"Otsuka",fullName:"Kenju Otsuka",slug:"kenju-otsuka"}]},{id:"8450",title:"Surface-Emitting Circular Bragg Lasers – A Promising Next-Generation On-Chip Light Source for Optical Communications",slug:"surface-emitting-circular-bragg-lasers-a-promising-next-generation-on-chip-light-source-for-optical-",signatures:"Xiankai Sun and Amnon Yariv",authors:[{id:"4201",title:"Prof.",name:"Xiankai",middleName:null,surname:"Sun",fullName:"Xiankai Sun",slug:"xiankai-sun"},{id:"122981",title:"Dr.",name:"Amnon",middleName:null,surname:"Yariv",fullName:"Amnon Yariv",slug:"amnon-yariv"}]},{id:"8451",title:"Novel Enabling Technologies for Convergence of Optical and Wireless Access Networks",slug:"novel-enabling-technologies-for-convergence-of-optical-and-wireless-access-networks",signatures:"Jianjun Yu, Gee-Kung Chang, Zhensheng Jia and Lin Chen",authors:[{id:"8503",title:"Dr.",name:"Jianjun",middleName:null,surname:"Yu",fullName:"Jianjun Yu",slug:"jianjun-yu"},{id:"133376",title:"Prof.",name:"Gee-Kung",middleName:null,surname:"Chang",fullName:"Gee-Kung Chang",slug:"gee-kung-chang"},{id:"133378",title:"Prof.",name:"Zhensheng",middleName:null,surname:"Jia",fullName:"Zhensheng Jia",slug:"zhensheng-jia"},{id:"139599",title:"Prof.",name:"Lin",middleName:null,surname:"Chen",fullName:"Lin Chen",slug:"lin-chen"}]},{id:"8452",title:"Photonic Crystal Multiplexer/Demultiplexer Device for Optical Communications",slug:"photonic-crystal-multiplexer-demultiplexer-device-for-optical-communications",signatures:"Sahbuddin Shaari and Azliza J. M. 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De Rooij",slug:"n.f.-de-rooij"}]}]}]},onlineFirst:{chapter:{type:"chapter",id:"73350",title:"Pleistocene Climate Change in Central Europe",doi:"10.5772/intechopen.93820",slug:"pleistocene-climate-change-in-central-europe",body:'\n
\n
1. Introduction
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Definition of loess: It is s a terrestrial, clastic sediment, composed dominantly of silt-sized particles and formed by the accumulation of wind-blown dust. It covers up to 10% of the world’s surface area and is usually inter-bedded with paleosol horizons forming loess-paleosol sequences, or LPS [1]. Such successions provide very detailed insight into Pleistocene climatic fluctuations [2, 3, 4]. Due to this characteristic, LPS’s provide very good records of palaeoclimate and environmental changes in the Pannonian Basin for at least 1 Ma [5]. The region of Baranja situated in the north-eastern part of Croatia is located in the southern edge of Pannonian Basin which is a part of Central Europe (Figure 1). It was selected for this research because some of the thickest loess successions in Croatia are exposed along the Danube River in Baranja. The total thickness of these loess deposits (above and under the surface) probably exceeds 50 m [6]. The Zmajevac locality was selected because it is accessible, contains four paleosols in loess and has a total thickness of almost 20 m. Grain-size distribution indicates that the loess from Zmajevac LPS in Baranja is typical loess, comparable with other loess profiles in the Pannonian Basin [3, 4].
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Figure 1.
Pannonian Basin with loess profiles from Croatia, Serbia and Hungary marked with red polygons. Neanderthal and early modern human sites marked with black triangles (Krapina and Vindija in Croatia) and yellow squares (Remete Felsö and Šal’a in Slovakia). This position map is made and adjusted by using a global multi-resolution topography map [78] (http://www.geomapapp.org).
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The LPS of Baranja and northeastern Croatia have a long history of investigation [7, 8]. The molluscan fauna within LPS were investigated and provided an overview on warm periods in the Late Pleistocene of northeastern Croatia [9]. Other researchers focused on the molluscan fauna from LPS at the Vukovar and Ðakovo loess plateaus, situated 20–30 km south of Baranja region [10, 11, 12].
\n
Focus of this chapter is to describe the climate change during the Late Pleistocene based on the δ18O and δ13C values measured in land-snail (mollusk) shells from loess samples of the Zmajevac LPS. Overall, the results of this study will provide a better insight into the impact of climate change on the populations of Neanderthals and anatomically modern humans (AMH) in Central Europe, and the disappearance of the aforementioned. Emphasis is on δ18O values which are used for determination of paleotemperature changes. This is especially important because it provides the temperature changes during the appearance of AMH in Central Europe and the disappearance of the Neanderthals from the same region. The values of stable isotopes of oxygen (δ18O) and carbon (δ13C) can be used as a paleothermometer, as characteristic of mollusk assemblages [13, 14], or in a wider sense, as a tool to reconstruct the climatic conditions of the Late Pleistocene [15, 16, 17]. Previous research in the Pannonian Basin did not include stable isotope analysis of fossil mollusk shells for palaeoclimatic reconstructions in this specific time frame (130 ky - 20 ky). The only paper which included stable isotope analysis (δ18O values) as a part of a comprehensive loess study in this region is limited to the Last glacial maximum (LGM), which is only a part of MIS2 [18] and does not cover the entire Upper Pleistocene. Most researchers used mollusk assemblages only as a malaco-thermometer tool, and to establish mean annual temperature (MAT) values and/or average summer month temperatures represented by mean July temperatures – MJT [4, 14, 19]. Most recently, X-ray fluorescence (XRF) and magnetic susceptibility (MS) based palaeoclimatic data have been established in the Pannonian Basin and they determined the paleotemperatures in the 6.7–8.9°C range [20]. However, other researchers in Southern [21] and Western Europe [16, 22, 23], in Eastern Mediterranean [17, 24] and also in North America [15, 25, 26] used stable isotope analysis widely in the last three decades.
\n
Before using the stable isotope method in paleoenvironmental reconstruction it is necessary to understand the physical and chemical processes, or flux-balance model that takes place in mollusk shell <− > environment system. The most detailed explanation of that flux-balance model, and subsequent incorporation of isotope ratios in mollusk shells is given by Balakrishnan and Yapp [27]. The authors provide detailed insights into possible interpretational mistakes and constraints of this method and give all the necessary formulas which ensure better understanding of complex model used in palaeoclimatic research. That research lays the foundation for any future research which tends to use stable isotope data as a tool for paleoclimate or paleoenvironmental reconstruction.
\n
\n
\n
2. Research methods
\n
Field investigation and sampling in Baranja region is done during winter and early spring, because the lush vegetation in spring, summer and fall does not allow easy access to loess profiles (Figure 2). The aim of sampling is to identify the maximum thickness of chosen LPS. Bulk samples (8–10 kg) were collected from Zmajevac outcrop for malacological, sedimentological and stable isotope analysis.
\n
Figure 2.
Sampling at the Zmajevac LPS in Baranja region, Eastern Croatia. Beige colored sediment is loess and reddish – brown colored sediment is paleosol (Photo: Danijel Ivanišević).
\n
Samples for grain size analysis were decalcified with 5% HCL acid and dried in a heater for 24 h. Grain size analyses combined wet sieving and the pipette method. Classification of the grain size distribution was done according to [28]. Each loess sample was sieved to obtain whole mollusk shells for stable isotope analysis. Shells were derived from samples by screen-washing in distilled, deionized water for the purpose of saving primary ratios of stable oxygen and carbon isotopes. The identification of mollusk species followed taxonomic concepts that were established in previous researches [13, 29]. Assemblage analysis is done according to Ložek [13]. Selected mollusk shells are then prepared for stable isotope analysis. This was done in IAMC - CNR laboratory in Naples (Italy). First the shells were crushed into powder which is then heated to 500°C for 30 min to remove the organic matter. Ratios were measured by automated continuous flow carbonate preparation GasBench II device and Thermo Electron Delta Plus XP mass spectrometer. Acidification of samples was performed at 50°C. Every sixth sample was compared with an internal standard (Carrara Marble with δ18O = 2.43‰ versus VPDB; and δ13C = 2.43‰ vs. VPDB) and for every 30th samples, the NBS19 international standard was additionally measured. Standard deviations of carbon and oxygen isotope results were estimated as 0.1% and 0.08%, respectively and based on 20 measured samples, three times each.
\n
The magnetic mineral content recorded at Zmajevac LPS in a form of magnetic susceptibility (MS) signal was gathered from 44 samples collected into 200 ml plastic containers. Magnetic susceptibility measurements were performed in HGI-CGS laboratory, Zagreb (Croatia) using a Bartington MS2 device. Each sample was measured three times for better precision and statistical analysis.
\n
\n
\n
3. Results
\n
Grain-size analysis were also done in HGI-CGS laboratory, Zagreb (Croatia) following procedure by [30]. Results indicated silt as the dominant grain size fraction in all loess samples from the Zmajevac profile (Table 1). Average share of silt-size particles in samples is 88.11% and coarse-grained silt fraction is dominant with average percentage of 41.38%. The laminated horizon seen at the top of the middle part of the LPS, 1,5 m above the ladder (Figure 2) is composed of 81% sand, 11% silt and 8% clay. Silt dominance at the Zmajevac LPS confirms that this sediment was deposited during strong eolian activity in colder periods of Upper Pleistocene.
\n
\n
\n
\n
\n
\n
\n
\n\n
\n
Sample
\n
>0,063 mm
\n
0,032-0,063 mm
\n
0,016-0,032 mm
\n
0,004-0,016 mm
\n
<0,004 mm
\n
\n\n\n
\n
Kot 1/1
\n
12
\n
33
\n
31
\n
24
\n
0
\n
\n
\n
Kot 1/2
\n
8
\n
42
\n
23
\n
22
\n
5
\n
\n
\n
Kot 1/3
\n
5,5
\n
46,5
\n
24
\n
17
\n
7
\n
\n
\n
Kot 1/4
\n
11
\n
37
\n
22
\n
19
\n
11
\n
\n
\n
Kot 1/5
\n
7,5
\n
35,5
\n
28
\n
22
\n
7
\n
\n
\n
Kot 1/6
\n
9,5
\n
39,5
\n
27
\n
19
\n
5
\n
\n
\n
Kot 1/7
\n
14,5
\n
31,5
\n
27
\n
27
\n
0
\n
\n
\n
Kot 1/8
\n
8
\n
44
\n
27
\n
21
\n
0
\n
\n
\n
Kot 1/9
\n
12,5
\n
39
\n
24,5
\n
24
\n
0
\n
\n
\n
Zma 1/1
\n
15
\n
40
\n
20
\n
19
\n
6
\n
\n
\n
Zma 1/2
\n
14,5
\n
57,5
\n
12
\n
8
\n
8
\n
\n
\n
Zma 1/3
\n
10
\n
45
\n
28
\n
17
\n
0
\n
\n
\n
Zma 1/4
\n
12,5
\n
47,5
\n
25
\n
15
\n
0
\n
\n
\n
Average
\n
10,8
\n
41,4
\n
24,5
\n
19,5
\n
3,8
\n
\n\n
Table 1.
Grain size distribution in Zmajevac LPS.
\n
Magnetic susceptibility (MS) analysis provides the data about ferrimagnetic mineral content in sediment and/or soil. This is important because increased concentration of magnetic minerals indicates more humid and/or warmer climate conditions, while decreased concentration points to more arid and/or colder climate conditions. This method is also useful when data comparison from different localities is needed, in order to get the interpretation of palaeo-environmental evolution. MS values from Zmajevac LPS loess and loess like sediment range from 5 to 28.5 × 10–6 SI (Figure 3). MS values from L1 horizon from the upper part of the Zmajevac LPS range from 15 to 20 × 10–6 SI, which is typical for loess. The uppermost paleosol horizon (F2) shows the highest measured MS values within the LPS (82.5 × 10–6 SI). MS values in the loess unit L2 are again lower, with a mean of 14 × 10–6 SI and this is expected difference between loess and paleosol. However, one notable peak within this loess horizon was detected with MS value of 28.5 × 10–6 SI. The pedo-complex consisting of P3a and P3b paleosols is marked by significant peaks in MS values. They are however lower than MS values recorded in the F2 paleosol horizon. Upper paleosol F3a displays MS values of 67.7 × 10–6 SI, while underlying paleosol P3b displays MS values of 53.2 × 10–6 SI. Loess and loess like sediment under pedo-complex display MS values in range of 11 to 23.7 × 10–6 SI. The lowermost paleosol P4 shows again a somewhat higher MS value of 58.3 × 10–6 SI, and the lowermost loess horizon displays MS value of 25.1 × 10–6 SI.
\n
Figure 3.
MS values measured at Zmajevac LPS. Note: loess horizons in white and light gray color are numbered from 1 to 7. Four paleosols from top to bottom are: F2, F3a, F3b and F4; and they are represented with dark gray color.
\n
The mollusk paleontology of the Zmajevac LPS was analyzed from 13 bulk loess samples [30]. A total of 1705 terrestrial gastropod shells were collected. 13 species-level taxa was determined. Specimen richness related to the number of mollusk shells within the loess samples varies significantly in Zmajevac LPS. Results show that the malacofaunal shell concentration is moderate in lower loess horizons L7 (85) and L6 (117). It is strongly decreased in L5 (5) and L4 (7) loess horizons, and then increased in L3 (90), L2 (213), and L1 (136) loess horizons. The identified mollusk species have been classified according to their palaeoenvironmental preferences following previous, well documented research in Pannonian Basin [14, 19]. The presence and abundance of each mollusk species in loess samples can be used to determine paleoclimate and/or type of palaeovegetation. These information are basis for paleoenvironmental reconstruction that shaped the Pannonian Basin area during the deposition of loess sediment.
\n
Therefore, each sample is characterized by a certain malacofaunal assemblage [13]. The obtained quantified data [30] allowed the definition of mollusk assemblages in the Zmajevac LPS for each loess horizon (from top L1 to lowermost L7). Species tolerating open and dry habitats are abundant in the Zmajevac LPS. Five specific assemblages which are all cold – resistant were determined in 13 loess samples.
\n
\nHelicopsis striata assemblage is the most dominant among five assemblages detected in Zmajevac LPS. The Helicopsis striata assemblage indicates climate conditions preceding the last glacial/stadial maximum and it is characteristic assemblage of the ‘warm’ loess environment in Central Europe [13]. This ‘warm’ should not be considered warm in absolute terms, but relatively compared to the extremely cold periods during the Upper Pleistocene.
\n
\nChondrula tridens and Arianta arbustorum are generally abundant species in Zmajevac LPS, but their concentration in loess samples is never high enough for definition of a pure Chondrula tridens or Arianta arbustorum assemblage. This is not unusual, because it is not often that pure assemblages are found.
\n
\nArianta arbustorum species is cryogenic, hygrophilous species and related assemblage is typical for humid forests, hillsides and lowland areas.
\n
Contrary to that, Chondrula tridens species is a warm steppe species and related assemblage is representative of interstadial, mild, dry steppe to forest steppe environment.
\n
The Pupilla loessica and Columella columella assemblages are typical loess faunas and they represent glacial/stadial maximum. Arid and cold climate conditions are indicated by the Pupilla loessica assemblage, while more humid conditions are represented by the Columella columella assemblage.
\n
The two most common mollusk species which appear in all of the samples from the Zmajevac LPS are Helicopsis striata (WAGNER) and Arianta arbustorum (LINNAEUS). Precisely because of their presence in all loess horizons they were used for stable isotopes (δ18O and δ13C) analysis. They Stable oxygen isotope values for these two species range from −5.76‰ to −2.45‰ (Table 2). Stable carbon isotope values range from −8.83‰ to −6.84‰ (Table 2). Average value for δ18O is −3.91‰ and average value for δ13C is −7.95‰ (Table 2). It is obvious that δ13C values vary to a lesser extent than δ18O values. The values in each sample vary depending on which mollusk species is analyzed, but that is to be expected. Regularity, which would indicate that one analyzed mollusk species shows constantly lower or higher δ18O and δ13C values in relation to the other analyzed species, was not registered. The values for stable oxygen isotope are in accordance with results from other loess profiles in the Pannonian Basin with emphasis on MIS 2 stage [18].
\n
\n
\n
\n
\n\n
\n
Sample
\n
Stable oxygen (δ18O)
\n
Stable carbon (δ13C)
\n
\n\n\n
\n
Kot 1/1
\n
−2,45
\n
−7,45
\n
\n
\n
Kot 1/2
\n
−3,84
\n
−6,96
\n
\n
\n
Kot 1/3
\n
−4,05
\n
−6,84
\n
\n
\n
Kot 1/4
\n
−4,41
\n
−7,75
\n
\n
\n
Kot 1/5
\n
−3,26
\n
−8,83
\n
\n
\n
Kot 1/6
\n
−3,16
\n
−7,47
\n
\n
\n
Kot 1/7
\n
−4,85
\n
−8,04
\n
\n
\n
Kot 1/8
\n
−5,15
\n
−8,82
\n
\n
\n
Kot 1/9
\n
−5,27
\n
−8,31
\n
\n
\n
Zma 1/1
\n
−2,15
\n
−9,21
\n
\n
\n
Zma 1/2
\n
−3,35
\n
−8,62
\n
\n
\n
Zma 1/3
\n
−3,16
\n
−7,84
\n
\n
\n
Zma 1/4
\n
−5,76
\n
−7,23
\n
\n
\n
Average
\n
−3,91
\n
−7,95
\n
\n\n
Table 2.
Stable isotope values from Zmajevac LPS malacofauna. Upper four samples represent MIS 2 stage.
\n
\n
\n
4. Comparison of mollusk assemblages with others in Central Europe (Pannonian Basin)
\n
Data obtained from paleontological analysis from the Zmajevac LPS are valuable, but it is necessary to put them in a broader context and compare them with paleontological research from other sites in the Pannonian plain. Previous research of malacofauna conducted on loess profiles in Eastern Croatia [10, 12] show significant congruence with the results obtained by Banak et al. [30, 31] from the Zmajevac LPS.
\n
In Erdut loess profile [10] which is situated 30 km to the southeast from Zmajevac LPS determined malacofauna was detected in four loess horizons. The base horizon is characterized by a Columella columella assemblage, while in the three remaining horizons Helicopsis striata assemblages is dominant. These results are comparable and almost identical to the results obtained from the Zmajevac LPS on Bansko Brdo hill (30). Still, there are some minor differences in faunal assemblages that probably reflect micro climate conditions during the Upper Pleistocene. The L4, L5 and L6 loess horizons of the studied Zmajevac LPS with dominant Helicopsis striata assemblage show strong influence of Arianta arbustorum and Columella columella assemblage. In Erdut loess profile dominance of Helicopsis striata assemblage with minor influence of a Chondrula tridens assemblage is detected [10]. The topmost L1 horizon from this study and the topmost horizon from the Erdut LPS [10] display similarity, with the dominant Helicopsis striata assemblage being accompanied by a Chondrula tridens assemblage. The lowermost horizons at Zmajevac LPS (L7 and L6) and from the Erdut LPS [10] display differences which are marked by dominant Helicopsis striata assemblage at the Erdut profile and Columella columella assemblage at Zmajevac LPS.
\n
The mollusk species distribution of the Zmajevac LPS shows certain similarities also with the Irig loess profile on the southern slope of Fruška Gora Mt. in NW Serbia [2] which is less than 100 km away in east - southeast direction. Chondrula tridens and Helicopsis striata assemblages dominate in the Irig loess profile and are also present in the Zmajevac LPS, but Chondrula tridens is not so dominant in Zmajevac LPS. Further, in Irig loess profile Vallonia costata and Clausilia dubia species are present in the lowermost part of the LPS, but in contrast two lowermost loess horizons in the Zmajevac LPS bear cooler climate representative in form of Columella columella assemblage. This assemblage in Zmajevac LPS is reflecting the Middle Pleistocene Penultimate Glacial (MIS 6) conditions. Based on this compared data it is obvious that these two loess profiles are dominated by Helicopsis striata assemblage, but they differ significantly from each other, especially in lower horizons.
\n
The Upper Pleistocene malacofaunal assemblages from the Petrovaradin loess profile in NW Serbia show colder and more humid conditions than in either the Irig or Zmajevac LPS [3, 32]. This is probably an effect of the palaeogeographic position at the northern slope of Fruška Gora Mt. [3, 32], which is opposite to the positions of Zmajevac and Irig LPS’s at the southern slopes.
\n
The fauna from middle and upper loess horizons (L3, L2 and L1) of the Zmajevac LPS displays certain similarity also with Madaras loess section in South Hungary [33]. There are some differences present as well. Uppermost L1 loess horizon in the Zmajevac LPS differs from K L1 LL1 loess horizon in Madaras because Helicopsis striata and Chondrula tridens assemblages dominate here, while Columella columella and Vallonia tenuilabris species dominate in Madaras LPS. Also, oposite to Madaras LPS Columella columella species is scarce at Zmajevac LPS. L2 loess horizon from the Zmajevac LPS differs from K L1 LL2 loess horizon at Madaras section, because Vallonia costata and Pupilla muscorum species dominate in that LPS, while in the Zmajevac LPS Pupilla muscorum is present, but not dominant. Also, Vallonia costata species is not present at all. L3 loess horizon in the Zmajevac LPS and K L1 LL3 loess horizon from Madaras LPS both contain Helicopsis striata assemblage and show the greatest similarity.
\n
Described mollusk assemblages from Zmajevac LPS show small but important differences to other Pannonian Basin LPS’s. It is especially noticeable in loess horizons L7, L6 and L3 of Zmajevac LPS. Results of malacofaunal assemblages from nearby loess profiles in Serbia and Hungary suggest that climate conditions that dominated in this part of Central Europe were similar, with some differences which were a result of paleogeography and microclimate conditions driven by it.
\n
Sedimentological and magnetic susceptibility (MS) data obtained from Zmajevac LPS show similarities with other LPS’s in the Pannonian Basin that were described in last decade [2, 7, 8]. MS values are in the expected range, especially in loess horizons (Figure 3). MS values from four paleosols are comparable with those from Irig LPS in neighboring Vojvodina region [2]. The lowermost P4 paleosol from Zmajevac LPS displays significantly weaker signals, than the P2 paleosol, but it is stronger than signals from the overlying P3b paleosol horizon. The MS value of 58.3 × 10–6 SI in the P4 paleosol is lower than expected for a long, interglacial period in which favorable climatic conditions prevailed, thus enabling fully developed soil. Even though P4 is the oldest paleosol in Zmajevac LPS, a weaker signal than in the youngest F2 paleosol may indicate that the relatively low MS values are result of mineral leaching. Such a decrease in the MS signal in clayey horizons was also detected in LPS in Germany [34] and in Hungary [35], therefore, it is not a specificity of Zmajevac LPS. It is very likely that similar processes affected the P4 paleosol horizon in Zmajevac. In agreement with previous research of this area [7], the P4 horizon is correlated with the MIS 5e interglacial period. The pedo-complex forming paleosol horizons P3a and P3b is similar to a pedo-complex from the Vojvodina [2]. Reminiscent of synchronous horizon of Hungarian Sütto LPS [4], the signal from the P3 pedo-comlex is higher than the one measured in Vojvodina. Finally, the strongly increased MS value of 82.5 × 10–6 SI suggests that the uppermost paleosol P2 could represent an interglacial, rather than an interstadial phase.
\n
\n
\n
5. Late Pleistocene climate reconstruction based on δ18O and δ13C values
\n
Stable isotope ratios of δ18O and δ13C were measured from fossil shells of two species: Helicopsis striata and Arianta arbustorum. Modern European land snails are active in the +10 to +27°C temperature range and hibernate or become inactive at temperatures below +10°C [36, 37]. This implies that stable isotope ratios recorded in mollusk shells represent a warmer period when snails formed their shells. This period that spans from spring to fall can be 160–210 days long [38, 39] and it reflects an average growing season (AGS) temperature. The same principle can be applied on fossil snails. It is known that snails are active in building their shells during and immediately after the rain [40]. This information is crucial, because it provides a direct link from rainwater δ18O values and δ18O values that we measured in the mollusk shells. This complex relationship between the δ18O value of meteoric water and the values measured in land-snail shells has been studied for more than 40 years [15, 16, 17, 24, 41]. Today it is reliable and well established method often used for paleoclimate and paleoenvironmental research. Variations in land snail shell δ18O is a function of temperature, relative humidity, δ18O of water vapor, and δ18O of liquid water ingested by the snail [16, 27]. It is worth mentioning that intra-shell variation of values measured in snail shells from LGM ranges from 0‰ to −5.5‰ [18] in some studied areas.
\n
To avoid errors and to obtain the average δ18O and δ13C values, whole snail shells were crushed and analyzed. The δ18O value in mollusk shells is enriched on average by 5‰ relative to equilibrium with ingested rainwater [16]. This means that a δ18O value of palaeo rainwater incorporated in a mollusk shell which displays a δ18O value of approx. -3‰ was approx. -8‰.
\n
In order to compare climate conditions in the Upper Pleistocene with recent climate and to obtain relative temperature changes, it is necessary to know the δ18O values of recent meteoric water and recent AGS temperatures from the same or nearby region. The nearest measured δ18O value of rainwater to Zmajevac LPS is recorded in city of Zagreb, Croatia, which is located 250 km to the west from Zmajevac LPS. This δ18O value is −6.11‰ for summer months of June, July and August (JJA) and it is measured in the last two decades [18]. This values represent shorter periods than AGS, but it is the closest approximation as we can get. In the last two decades mean JJA temperature recorded in Zagreb was +19.7°C. If we compare δ18O values from Zmajevac LPS mollusk shells, enlarged for 5‰, we can clearly see that δ18O values of meteoric water in the Upper Pleistocene ranged from approx. -7.45‰ to approx. -10.76‰.
\n
If we compare these approximate and indirect δ18O values with δ18O value of −6.11‰ from present JJA measurements in Zagreb, it is clear that δ18O values were constantly lower/more negative. This means that AGS temperatures during the Upper Pleistocene in Baranj region were much lower than present temperature in city of Zagreb. The mean, annual δ18O value of rainwater for Zagreb is −8.33‰ [18] and mean annual temperature (MAT) for Zagreb in last two decades is +12°C. As most of the samples from Zmajevac LPS display more negative δ18O values than −8.33‰, we can say with some certainty that even the AGS temperatures (which represent the warmest period of the year) during the Upper Pleistocene were lower than the present MAT in Zagreb. It is hard to determine what was the absolute value of temperature in the Upper Pleistocene, but we can calculate relative values and compare them to present one.
\n
Researchers [42] estimated the MAT for MIS 2 stage is in range from 6.2°C to 11.2°C. It was reconstructed from oxygen isotopes values measured in mammoth tooth enamel from sites in the Czech Republic and Slovakia [42]. This paleotemperature data represents climate conditions from part of the Central Europe that is quite north of Zmajevac LPS (more than 200 km). Still, it can serve as a marker if we assume that the decrease in temperature is indeed related with latitude increase. Other researchers [20] estimated temperatures of 6.7 C (based on MS values), 8.5 ± 0.6 C (based on XRF-1 values) and 8.9 ± 4.4 C (based on XRF-2 values) in Northern Hungary for the same period of the Upper Pleistocene (MIS 2 stage). Finally, researchers [43] calculated a MAT of 4.5 C in Central Europe using noble gas thermometry (NGT). This result displays significantly lower MAT than other results, which is probably due to this specific method.
\n
Results from our research show that δ18O values from Zmajevac LPS are in fair accordance with δ18O values from North America and other LPS’s in Central Europe, but they are partly different from δ18O values from southern Europe (Figure 4).
\n
Figure 4.
Comparison of results for MIS2 from Zmajevac LPS with ones recorded in other European and north American LPS profiles from late Pleistocene.
\n
δ18O values measured in fossil shells indirectly reflect paleotemperature at a time when these fossil snails lived. This is useful if we want to reconstruct paleotemperature changes over longer period of time if we have enough data, that is, fossil findings. We know from previous research that if the δ18O value in the shell changes by 0.5‰ it reflects a paleotemperature change of approximately 2°C [24]. The formula for calculating AGS paleotemperature changes in the Zmajevac LPS, adjusted according to [24], is as proposed:
δ18 Omax. is: maximal δ18O value measured in a gastropod shell
\n
δ18 Omin. is: minimal δ18O value measured in a gastropod shell
\n
We used the δ18O values measured from Zmajevac LPS fossil shells and according to this formula AGS paleotemperature changes through entire Upper Pleistocene in Baranja region is: 13.2°C.
\n
Other researchers propose different ratios and interdependence of δ18O values and paleotemperature. According to [26] if the δ18O value in shell changes by 0.35‰ it reflects a paleotemperature change of approximately 1°C. We can adjust the formula according to this research and then it is:
δ18 Omax. is: maximal δ18O value measured in a gastropod shell
\n
δ18 Omin. is: minimal δ18O value measured in a gastropod shell
\n
If we use the same δ18O values from Zmajevac LPS fossil shells in this formula, AGS paleotemperature changes through the Upper Pleistocene in Baranaj region is: 9.5°C.
\n
If we compare these results with MAT temperatures for other Pannonian Basin LPS, it is plausible to conclude that the second formula and the range of 9.5°C are more accurate. Both of these values suggest strong and constant changes of paleotemperature during the Upper Pleistocene in the Baranja region.
\n
It is worth mentioning that he δ18O values from Zmajevac LPS displays some deviation in regards to paleotemperatures or paleoclimate conditions determined by malacofaunal assemblages. These deviations are probably a result of complex flux-balance model between the rainwater used by the fossil snails and their shell, which does not respond with the same intensity to palaeo temperature changes [27].
\n
Climate changes during the glacial and interglacial periods are the main cause for changes in vegetation which are reflected in δ13C values of plants [44, 45]. Therefore, δ13C values from fossil shells can be used to determine the diet of land snails, which can then help in palaeoenvironmental reconstruction. The δ13C value of atmospheric CO does not affect the δ13C value of snail shells, so these values are a relevant and reliable indicator of fossil snail diet [27]. If the δ13C values are more negative, it is an indication that the mollusks consumed more C3 plants in their diet and that the climate was cooler and more humid [22, 25]. If the δ13C values are more positive, it is an indication that the snails consumed more C4 plants in their diet, which indicates a more arid environment [22, 46].
\n
Research from central parts of Pannonian Basin (Hungary) [47] shows that relatively stable woodland-grassland ecotone was the dominant vegetation type in the Pannonian Basin between 140 ky and 16 ky. This is a time span which largely coincides with Upper Pleistocene period. Described woodland-grassland ecotone was preserved even during the strongest cooling, when a treeless steppe dominated the landscape of Pannonian Basin [47]. In this mixture of temperate, arctic and alpine ecosystems C3 plants typically dominate [48]. Soils formed in Tokaj region (southern Hungary) at the southern edge of the Pannonian Basin, display δ13C values in really narrow range from −24‰ to −25‰ [48]. This is typical for soils developed under plants using the C3 photosynthetic pathway [49].
\n
The variation of δ13C values measured in fossil shells from Zmajevac LPS loess samples ranges from −8.83‰ to −6.84‰. Therefore, C4 vegetation as a diet source for these fossil snails obtained from Zmajevac LPS can be excluded. C4 plants display very different δ13C values, ranging from −8‰ to −16‰ [49] and this is contrary to our results from Baranja region. δ13C values measured in any fossil mollusk shells are enriched by 8–19‰ compared to the values of the plants that they ingested [50]. This means that δ13C values of plants that mollusk from Zmajevac LPS ingested, were approximately in the range from −14.84‰ to −16.83‰, if we use the minimal 8‰ enrichment approach. This is very close to the most negative margin for C4 plants. If we apply maximal 19‰ enrichment, these values are more negative and in range from −25.84‰ to −27.83‰. Results from nearby areas [2, 4, 47, 48] that were compared with the results from this study suggests that for the entire time span during which the Zmajevac LPS was accumulated, C3 plants have been the main vegetation type for analyzed fossil snails. This indicates that Upper Pleistocene climate in the Baranja region was similar to the paleoclimate in other regions in the Pannonian Basin. Certain differences in paleoclimate exist and they are probably an effect of local geomorphology and microclimate conditions.
\n
\n
\n
6. Impact of paleoclimate changes on Neanderthals and anatomically modern humans (AMH) in Central Europe
\n
The Balkan peninsula was likely the migration route of anatomically modern humans (AMH) into Europe [51], and the Danube valley which cuts the Pannonian Basin is one of the most important pathways of these population movements [52]. This region consists of vast lowlands associated with the middle Danube drainage basin and surrounded by the Carpathian Mountains, the Alps, Dinarides and the Bohemian Massif. The Last Glacial loess provides widely extended sedimentary coverage of the area and provides valuable paleoclimate records [2, 3, 4]. Additional stratigraphic records are present in caves located in the highlands and peripheral mountain zones. The Zmajevac LPS, described above is located in this region. This geographical setting allows us to determine with considerable certainty the impact of climate change in the Late Pleistocene on Neanderthal and early modern human populations.
\n
The Neanderthals clearly represent the autochthonous population of eastern Central Europe according to various research [53, 54, 55]. This is documented by a group of fossil finds, spread over space and time and in the various environments, ranging from the last interglacial to the temperate oscillations of the early Würmian glacial (OIS 5a–e). Some of the most important fossil finds of Neanderthals and AMH are located in the Pannonian Basin, especially in its central, western and southern parts (Figure 1). Here we briefly describe localities from Pannonian Basin: two in Croatia, one in Hungary and one in Slovakia.
\n
\nKrapina (Croatia): Excavated layers 3–8 yielded more than 900 skeletal fragments of several Neanderthal individuals, especially cranial fragments, mandibles, teeth, and postcranial fragments. This makes Krapina one of the most important Neanderthal sites in Europe. ESR and U-series dating provided results between 178 and 120 ka, with average values pointing to 130 ka, i.e., to the last interglacial peak OIS 5e [56]. The Lithic industry is a variant of the Mousterian.
\n
\nVindija, G3 layer (Croatia): All layers in this cave are characterized by abundance of cave bear skeletal remains, especially in some of the layers. Within the sequence of the Mousterian industries, the Neanderthal fossils [54] appear in layer G3 in association with some endscrapers and possible leaf-point fragments [57, 58]. Age of neanderthal tibia fragment in G3 layer was dated and it is 38 ka B.P. [59].
\n
\nVindija G1 layer (Croatia): This layer yielded several human fragments of archaic morphology, which do not differ radically from the Neanderthals of the underlying layers and elsewhere in Central Europe [54]. However, the associated lithics, even if typical for the Initial Upper Paleolithic period in general, allow for somewhat contradictory interpretations. The leaf point suggests the Szeletian industry [59] and on the other hand the bone split-base point and the Mladeč type point suggest an Aurignacian [57, 60]. The Aurignacian industry that marked replacement of Neanderthals by anatomically modern humans (AMH) lasted from 43 to 26 ka years B.P. and it is characterized by worked bone or antler points with grooves cut in the bottom [61]. Their flint tools include fine blades struck from prepared cores rather than using crude flakes [61]. Mester [62] describes the problem of distinguishing these two cultural units and points to a possibility that Szeletian tools had been made by AMH. From this point of view Szeletian represents a sub variant of the Aurignacian. In this interpretation, Aurignacian bone points may have been the functional equivalents of Szeletian bifacial leaf points.
\n
The associated bear bones were dated to 36–32 ka B.P., but dating of the human bones provided AMS radiocarbon dates of 29–28 ka B.P. [63]. Given the association of these objects in an 8–20 cm thick layer which is partially cryoturbated, we cannot exclude the possibility of some mixture of fossils and artifacts of various ages, as some researchers suggest [60]. However, since the two types of projectiles—the lithic leaf points and the polished bone-and-antler points – appear together in several other cave sites of the region (Dzeravá skala, Mamutowa Cave, Istá lloskö Cave, etc.) [64], it is rather unlikely that mechanical mixing was responsible in all cases. It seems that associations of these projectiles made from different materials and thus with different advantages and functions [65] with predefined cultures may not be as local as expected. The “Aurignacian” bone projectiles are actually being found more frequently in non-Aurignacian contexts, not only in the Central European caves, but also in other regions as far away as northeast Russia [57, 60]. This indicates that certain communication between separated Neanderthal groups could have existed.
\n
\nRemete Felsö (Hungary): The stratigraphy of this cave includes two glacial horizons or layers marked as: 5 and 4. The upper one, which is a layer characterized by loess containes limestone debris. Three human teeth (right I1-I2 and C) belonging to the same individual were found and analyzed. They are rather large and worn, but nothing more can be said about their specific features. The fauna, including cave bears, hyenas, lions and musk ox, suggests a tendency to cooling between the lower and upper horizon. All this faunal remains point to Szeletian in sensu latu and age is determined as OIS 3 [65]. The associated industry is characterized by typical leaf points and retouched flakes (including a Levallois flake), and has been classified generally as Szeletian, or, as a specific Transdanubian form of the late Middle Paleolithic—the Jankovichian [66].
\n
\nŠal’a (Slovakia): Two Neanderthal cranial fragments, Šal’a 1 and the subsequently discovered Šal’a 2, were found in two different locations in the Vah river gravel deposits, but in secondary position and without precise dating. According to the correlation of the phylogenetic stratigraphic ranges of the vertebrate finds, the primary position of the Neanderthal Šaľa 1 specimen could be–with high probability – set into the terrestrial layers of the last interglacial age, approx. 100–75 ka years B.P., which fits into OIS 5 stage [67].
\n
Generally, eastern part of Central Europe provides solid evidence for the association of Neanderthals with the various Middle Paleolithic cultural entities of the interglacial and early glacial: the Taubachian, Mousterian, and Micoquian [68, 69]. Recent findings from the Neanderthal type locality Kleine Feldhofer Grotte site in the Neander Valley (Germany) also provide solid insights in various Middle and Upper Paleolithic cultural entities [70]. Preliminary analysis of the thousands of lithic artifacts recovered from this site has shown that two specific Paleolithic assemblages are represented: Micoquian artifacts typical of the late Middle Paleolithic and Upper Paleolithic artifacts from the Gravettian [70].
\n
The question of the last Neanderthals and their relationship to the transitional or Initial Upper Paleolithic cultural entities of the region—the Szeletian and the Bohunician is far more susceptible to debate. Their “transitional” character is understood as a combination of archaic Middle Paleolithic patterns in technology, combined with the introduction of Upper Paleolithic tool-types [69].
\n
The moment of AMH appearance in the Balkans and Central Europe has become better documented, since the new discovery at Pestera çu Oase 36–34 ka B.P. [71] and revisions of human fossil sites such as Mladeč which points to age of 35–34 ka B.P. In addition, the expansion of Aurignacian sites in Central Europe shows a specific time and space dynamic. While the early Aurignacian sites, dated as early as 42 ka B.P., are extremely rare and isolated (Willendorf II in Austria and Geissenklösterle in Germany) [72, 73, 74], the middle Aurignacian, dated between 34 and 29 ka years B.P., forms a kind of network of sites over large parts of the region. It also includes the emergence of Aurignacian figurative art. This findings point to interesting and probable conclusion. If the Aurignacian can be identified with AMH then the increased site density reflects their demographic growth. Also, if the art represents their higher social complexity and more advanced cognitive abilities, then the whole process may demonstrate the final “victory” of AMH over Neanderthals in Central Europe.
\n
Various authors have listed several possible reasons for the extinction of Neanderthals. Some have discussed the possibility that their extinction was stimulated by violent conflict with Homo sapiens [75]. Violence in early hunter-gatherer societies usually occurred as a result of resource competition following major natural disasters. Another possibility, proposed recently is the spread of pathogens or parasites carried by Homo sapiens into the Neanderthal population [76]. The fact of coexistence also leaves open the possibility of interbreeding which resulted with a genetic heritage left by the Neanderthals in the anatomically modern human (AMH) population of the Upper Paleolithic Europe.
\n
Neanderthals possessed the brain that enabled them greater visual acuity than Homo sapiens did, but the latter had better language-processing abilities [77]. It can be stated with certainty that Neanderthal brains were more adapted to vision and spatial memory and that resulted in less available area for cognition and social interactions [77]. This difference in brain structure could also lead to extinction of Neanderthals during short period of competition with Homo sapiens.
\n
A separate set of factors that are not connected to the interaction of Neanderthals and AMH are climate change and natural disasters. It is well documented and described that the general characteristic of the paleoclimate in Central Europe (particularly in Pannonian Basin) is repeated succession of oscillations with varying intensity. This climate teeter started with an expansion of dense forests during the interglacial peak (OIS 5e). In OIS 5e the climate was very similar to today’s climate. It continued throughout the long transitional stage of the early glacial (OIS 5a–d) with several oscillations that shaped a dry, steppe environment [2, 4, 5, 31]. This climate change has affected the whole region, but we must not forget that geomorphology has conditioned specific micro-climatic conditions within [2, 4, 20, 31]. As discussed in this book chapter, climate change was constant during the Upper Pleistocene in Central Europe. Average summer temperature changes were in range from 9.5°C and up to 13.2°C [24, 26, 31] compared to present day temperatures which are significant changes that have certainly affected the Neanderthal population.
\n
Climate changes during the glacial and interglacial periods were also the main cause for changes in vegetation. C3 plants have been most probably the main vegetation type during the Late Pleistocene. These include trees and cold steppe grasses [31]. Changes in plant life were reflected in herbivore, mammal population and they would have led to a corresponding decline in big, plant-eating mammals hunted by the Neanderthals [78].
\n
From the aforementioned sites and findings within, we can assume that the Neanderthal extinction in eastern Central Europe was not the result of just adverse climatic conditions during the Lower Pleniglacial maximum (OIS 4), but rather originated from several millennia of coexistence with the emerging early modern humans during the OIS 3 [79]. Data indicate that the disappearance of Neanderthals occurred at different times in different regions of Europe and Asia. Comparing the data with results obtained from the earliest dated AMH sites in Europe allowed the quantification of the temporal overlap between the two groups. The results reveal a significant overlap of 2600–5400 years (at 95.4% probability) [78]. It is clear that the coexistence with AMH population was long enough for the transmission of cultural and symbolic behavior, as well as possible genetic exchanges (interbreeding), between the two groups [78], but it is hard to conclude that it was the main cause of Neanderthal extinction. After the interbreeding episode(s), Neanderthals and their material culture disappeared and was replaced across Europe and Asia by AMH [79]. The precise timing of this transitional period has remained difficult to identify in the absence of a reliable chronological framework [79, 80].
\n
In the end and as the most obvious conclusion, we can say that the extinction of Neanderthals and the rise of AMH population in Central Europe is due to a combination of all the factors mentioned in above, but it is difficult to reliably determine which one prevailed.
\n
\n
\n
7. Conclusion
\n
Data obtained from sedimentological and magnetic susceptibility analysis of Zmajevac LPS show a fairly good similarity with results from other LPS’s in the Pannonian Basin [2, 4, 8]. Stable oxygen values measured in fossil snail shells show significant paleotemperature changes during the Upper Pleistocene in the Baranja region. Average growing season (AGS) temperature changes during that period were 13.2°C [24] or 9.5°C [26], depending on which formula is applied. The second calculated value is more plausible and in accordance with other results from Pannonian Basin. The overall climate was much cooler then present day climate. Stable carbon isotope values show that the C3 plants have been the main vegetation type of fossil snails for the entire time span during which the Zmajevac LPS was accumulated. This indicates that they lived in environment dominated by trees and cold steppe grasses. Comparison of the results from Zmajevac LPS with other LPS’s from Central Europe [2, 4, 81] suggests that Upper Pleistocene climate in the Baranja region was similar to the paleoclimate in other regions in the Pannonian Basin. Certain differences in paleoclimate existed and they are probably an effect of local geomorphology and microclimate conditions.
\n
The described climate change in the Upper Pleistocene is very likely a significant but not the only factor that influenced the extinction of the Neanderthal population which paved the way for the dominance of anatomically modern humans (AMH) in Central Europe and everywhere else in the World.
\n
\n\n',keywords:"Pleistocene, climate change, loess, stable isotopes, Central Europe, Neanderthals",chapterPDFUrl:"https://cdn.intechopen.com/pdfs/73350.pdf",chapterXML:"https://mts.intechopen.com/source/xml/73350.xml",downloadPdfUrl:"/chapter/pdf-download/73350",previewPdfUrl:"/chapter/pdf-preview/73350",totalDownloads:110,totalViews:0,totalCrossrefCites:1,dateSubmitted:"September 17th 2019",dateReviewed:"August 31st 2020",datePrePublished:"October 15th 2020",datePublished:"December 23rd 2020",dateFinished:"September 25th 2020",readingETA:"0",abstract:"Loess is terrestrial, clastic sediment formed by the accumulation of wind-blown dust. It is usually inter–bedded with paleosol horizons, forming loess-paleosol successions (LPS). Due to their characteristics LPS’s represent valuable records of climate changes during Pleistocene. The thickest LPS sections in Croatia are in the Baranja region. Stable oxygen (δ18O) and carbon (δ13C) isotope analysis were made on loess malacofauna in order to quantify paleo-temperature changes and describe paleo-vegetation in this part of Central Europe. δ18O values show significant paleotemperature changes during the Upper Pleistocene (130 ky - 20 ky) in Baranja region. Average growing season (AGS) temperature varied 13.2 °C or 9.5 °C during that time period, depending on which formula is applied for calculations. Magnetic susceptibility (MS) measurements show strong peaks in the paleosol horizons pointing to more humid climate. The overall climate was much cooler then present. Stable carbon isotope values point to dominance of C3 vegetation type during the Late Pleistocene in southern part of Central Europe. Climate change in the Late Pleistocene is very likely a significant but not the only factor that influenced the extinction of Neanderthal population which paved the way for the dominance of anatomically modern humans (AMH) in Central Europe.",reviewType:"peer-reviewed",bibtexUrl:"/chapter/bibtex/73350",risUrl:"/chapter/ris/73350",signatures:"Adriano Banak, Oleg Mandic, Davor Pavelić, Marijan Kovačić and Fabrizio Lirer",book:{id:"9251",title:"Pleistocene Archaeology",subtitle:"Migration, Technology, and Adaptation",fullTitle:"Pleistocene Archaeology - Migration, Technology, and Adaptation",slug:"pleistocene-archaeology-migration-technology-and-adaptation",publishedDate:"December 23rd 2020",bookSignature:"Rintaro Ono and Alfred Pawlik",coverURL:"https://cdn.intechopen.com/books/images_new/9251.jpg",licenceType:"CC BY 3.0",editedByType:"Edited by",editors:[{id:"177123",title:"Ph.D.",name:"Rintaro",middleName:null,surname:"Ono",slug:"rintaro-ono",fullName:"Rintaro Ono"}],productType:{id:"1",title:"Edited Volume",chapterContentType:"chapter",authoredCaption:"Edited by"}},authors:[{id:"109384",title:"Dr.",name:"Fabrizio",middleName:null,surname:"Lirer",fullName:"Fabrizio Lirer",slug:"fabrizio-lirer",email:"fabrizio.lirer@iamc.cnr.it",position:null,institution:{name:"Institute for Coastal Marine Environment",institutionURL:null,country:{name:"Italy"}}},{id:"312107",title:"Dr.",name:"Adriano",middleName:null,surname:"Banak",fullName:"Adriano Banak",slug:"adriano-banak",email:"adrianobanak@gmail.com",position:null,institution:null},{id:"315450",title:"Prof.",name:"Davor",middleName:null,surname:"Pavelić",fullName:"Davor Pavelić",slug:"davor-pavelic",email:"dpavelic@rgn.hr",position:null,institution:null},{id:"315451",title:"Prof.",name:"Marijan",middleName:null,surname:"Kovačić",fullName:"Marijan Kovačić",slug:"marijan-kovacic",email:"mkovacic@geol.pmf.hr",position:null,institution:null},{id:"315452",title:"Dr.",name:"Oleg",middleName:null,surname:"Mandic",fullName:"Oleg Mandic",slug:"oleg-mandic",email:"oleg.mandic@nhm-wien.ac.at",position:null,institution:null}],sections:[{id:"sec_1",title:"1. Introduction",level:"1"},{id:"sec_2",title:"2. Research methods",level:"1"},{id:"sec_3",title:"3. Results",level:"1"},{id:"sec_4",title:"4. Comparison of mollusk assemblages with others in Central Europe (Pannonian Basin)",level:"1"},{id:"sec_5",title:"5. Late Pleistocene climate reconstruction based on δ18O and δ13C values",level:"1"},{id:"sec_6",title:"6. Impact of paleoclimate changes on Neanderthals and anatomically modern humans (AMH) in Central Europe",level:"1"},{id:"sec_7",title:"7. Conclusion",level:"1"}],chapterReferences:[{id:"B1",body:'\nPecsi, M. Loess. In: Fairbridge, R.W. (Ed.). The Encyclopedia of Geomorphology. Reinhold, New York, 1968, pp. 674-678.\n'},{id:"B2",body:'\nMarković, S.B., Oches, E.A., McCoy, W.D., Gaudenyi, T., Frechen, M., Jovanović, M. Malacological and sedimentological evidence for ‘warm’ climate from the Irig loess sequence (Vojvodina, Serbia). Geophysics, Geochemistry and Geosystems. 2007: 8, Q 09008.\n'},{id:"B3",body:'\nMarković, S.B., Bokhorst, M.P., Vandenberghe, J., McCoy, W.D., Oches, E.A., Hambach, U., Gaudenyi, T., Jovanović, M., Zöller, L., Stevens, T., Machalett, B. Late Pleistocene loess-paleosol sequences in the Vojvodina region, north Serbia. Journal of Quaternary Science. 2008: 23: 73-84.\n'},{id:"B4",body:'\nNovothny, A., Frechen, M., Horvath, E., Wacha, L., Rolf, C. Investigating the penultimate and last glacial cycles of the Sütto loess section (Hungary) using luminescence dating, high-resolution grain size, and magnetic susceptibility data. Quaternary International. 2011: 234: 75-85.\n'},{id:"B5",body:'\nMarković, S.B., Hambach, U., Stevens, T., Kukla, G.J., Heller, F., McCoy, W.D., Oches, E.A., Buggle, B., Zöller, L. The last million years recorded at the Stari Slankamen (Northern Serbia) loess-paleosol sequence: revised chronostratigraphy and long-term environmental trends. Quaternary Science Reviews. 2011: 30: 1142-1154.\n'},{id:"B6",body:'\nBanak, A. Reconstruction of Late Pleistocene Climate Change Based on Loess Sedimentology, Malacofaunal Palaeontology and Isotope Analysis (Baranja, Eastern Croatia) (Ph.D. thesis). University of Zagreb, Croatia (in Croatian, with English Abstract); 2012.\n'},{id:"B7",body:'\nGalović, L., Frechen, M., Halamić, J., Durn, G., Romić, M. Loess chronostratigraphy in Eastern Croatia – a luminescence approach. Quaternary International. 2009: 198: 85-97.\n'},{id:"B8",body:'\nWacha, L., Frechen, M. The chronology of the “Gorjanović loess section” in Vukovar, Croatia. Quaternary International. 2011: 240: 87-99.\n'},{id:"B9",body:'\nRukavina, D. O stratigrafiji gornjeg pleistocena s osvrtom na topla razdoblja i njihov odraz u naslagama na području Jugoslavije (On stratigraphy of the Late Pleistocene with review of warm periods and their reflection in the area of Yugoslavia). 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GeoJournal. 1995: 36: 213-222.\n'},{id:"B15",body:'\nYapp, C.J. Oxygen and carbon isotope measurements of land snail shell carbonate. Geochimica et Cosmochimica Acta. 1979: 43: 629-635.\n'},{id:"B16",body:'\nLecolle, P. The oxygen isotope composition of landsnail shells as a climatic indicator: applications to hydrogeology and paleoclimatology. Chemical Geology. 1985: 58: 157-181.\n'},{id:"B17",body:'\nGoodfriend, G.A. The use of land snail shells in paleoenvironmental reconstruction. Quaternary Research. 1992: 11: 665-685.\n'},{id:"B18",body:'\nKehrwald, N., McCoy, W.D., Thibeault, J., Burns, S.J., Oches, E.A. Paleoclimatic implications of the spatial patterns of modern and LGM European land-snail shell δ18 O. Quaternary Research. 2010: 74: 166-176.\n'},{id:"B19",body:'\nSümegi, P., Krolopp, E. Quatermalacological analysis for modeling of the Upper Weichselian palaeoenvironmental changes in the Carpathian Basin. Quaternary International. 2002: 91: 53-63.\n'},{id:"B20",body:'\nSchatz, A.-K., Scholten, T., Kühn, P. Paleoclimate and weathering of the Tokaj (NE Hungary) loess-paleosol sequence: a comparison of geochemical weathering indices and paleoclimate parameters. Climate of the Past. 2014: 10: 469-507. Discussions.\n'},{id:"B21",body:'\nColonese, A.C., Zanchetta, G., Fallick, A.E., Martini, F., Manganelli, G., Lo Vetro, D. Stable isotope composition of Late Glacial land snail shells from Grotta del Romito (Southern Italy): palaeoclimatic implications. Palaeogeography, Palaeoclimatology, Palaeoecology. 2007: 254: 550-560.\n'},{id:"B22",body:'\nYanes, Y., Delgado, A., Castillo, C., Alonso, M.R., Ibáñez, M., De La Nuez, J., Kowalewski, M. Stable isotope (δ18 O, δ 13C, and δD) signatures of recent terrestrial communities from a low-latitude, oceanic setting: endemic land snails, plants, rain, and carbonate sediments from the eastern Canary Islands. Chemical Geology. 2008: 249: 377-392.\n'},{id:"B23",body:'\nYanes, Y., Romanek, C.S., Delgado, A., Brant, H.A., Noakes, J.E., Alonso, M.R., Ibáñez, M. Oxygen and carbon isotopes of modern land snail shells as environmental indicators for a low-latitude oceanic island. Geochimica et Cosmochimica Acta. 2009: 73: 4077-4099.\n'},{id:"B24",body:'\nGoodfriend, G.A. Terrestrial stable isotope records of Late Quaternary paleoclimates in the eastern Mediterranean region. Quaternary Science Reviews. 1999: 18: 501-513.\n'},{id:"B25",body:'\nGoodfriend, G.A., Ellis, G.L. Stable carbon and oxygen isotope variations in modern Rabdotus land snail shells in the southern Great Plains, USA, and their relation to environment. Geochimica et Cosmochimica Acta. 2002: 66: 1987-2002.\n'},{id:"B26",body:'\nBalakrishnan, M., Yapp, C.J., Meltzer, D.J., Theler, J.L. Palaeonvironment of the Folsom archaeological site, New Mexico, USA, approximately 10,500 14C B.P. as inferred from the stable isotope composition of fossil land snail shells. Quaternary Research. 2005: 63: 31-44.\n'},{id:"B27",body:'\nBalakrishnan, M., Yapp, C.J. Flux balance models for the oxygen and carbon isotope composition of land snail shells. Geochimica Cosmochimica Acta. 2004: 68: 2007-2024.\n'},{id:"B28",body:'\nWentworth, C.K. A scale of grade and class terms for clastic sediment. The Journal of Geology. 1922: 30: 377-392.\n'},{id:"B29",body:'\nFrank, C. Plio-pleistozäne und holozäne Molluscen Österreichs. Verlag der Österreichischen Akademie der Wissenschaften; 2006. 797p.\n'},{id:"B30",body:'\nBanak, A., Mandic, O., Kovačić, M., Pavelić, D. Late Pleistocene climate history of the Baranja loess plateau-evidence from the Zmajevac loess-paleosol section (northeastern Croatia). Geologia Croatica 2012: 65 (3): 411-422.\n'},{id:"B31",body:'\nBanak, A., Mandic, O., Sprovieri, M., Lirer, F. & Pavelić, D. Stable isotope data from loess malacofauna: Evidence for climate changes in the Pannonian Basin during the Late Pleistocene. Quaternary International. 2016: 415: 15-24.\n'},{id:"B32",body:'\nMarković, S.B., McCoy, W.D., Oches, E.A., Savić, S., Gaudenyi, T., Jovanović, M., Stevens, T., Walther, R., Ivanišević, P., Galić, Z. Palaeoclimate record in the Upper Pleistocene loess-palaeosol sequence at Petrovaradin brickyard (Vojvodina, Serbia). Geologia Carpathica. 2005: 56: 545-552.\n'},{id:"B33",body:'\nHupuczi, J., Sümegi, P. The Late paleoenvironment and paleoclimate of the Madaras section (South Hungary), based on preliminary records from molluscs. Central European Journal of Geosciences. 2010: 2 (1): 64-70.\n'},{id:"B34",body:'\nRousseau, D.D., Antoine, P., Hatte, C., Lang, A., Zöller, L., Fontugne, M., Othman, D.B., Luck, J.M., Moine, O., Labonne, M., Bentaleb, I., Jolly, D. Abrupt millennial climatic changes Nussloch (Germany) Upper Weichselian eolian records during Last Glaciation. Quaternary Science Review. 2002: 21: 1577-1582.\n'},{id:"B35",body:'\nNovothny, Á., Frechen, M., Horváth, E., Bradak, B., Oches, E.A., McCoy, W.D. & Stevens, T. The loess profile at Süttő, Hungary. Quaternary International. 2009: 198: 62-76.\n'},{id:"B36",body:'\nHeller, J. Longevity in molluscs. Malacologia. 1990: 31: 259-295.\n'},{id:"B37",body:'\nThompson, R., Cheny, S., 1996. Raising Snails. National Agriculture Library. Special Reference Briefs Series No. SRB 96-05.\n'},{id:"B38",body:'\nFrömming, E. Biologie der Mitteleurop€aischen Landgastropoden. Deucher et Humboldt, Berlin. 1954.\n'},{id:"B39",body:'\nAnt, H. Faunistische, ökologische und tiergeographische Untersuchungen zur Verbreitung der Landschnecken in Nordwestdeutschland. Abhandlungen des Landesmuseums für Naturkunde Münster. 1963: 25: 125p.\n'},{id:"B40",body:'\nWard, D., Slowtow, R. The effects of water availability on the life history of the desert snail Trochoidea seetzeni: an experimental field manipulation. Oecologia. 1992: 90: 572-580.\n'},{id:"B41",body:'\nGoodfriend, G.A., Magaritz, M., Gat, J.R. Stable isotope composition of land snail body water and its relation to environmental waters and shell carbonate. Geochimica et Cosmochimica Acta. 1989: 53: 3215-3221.\n'},{id:"B42",body:'\nKovács, J., Moravcová, M., Újvári, G., Pintér, A.G. Reconstructing the paleoenvironment of East Central Europe in the Late Pleistocene using the oxygen and carbon isotopic signal of tooth in large mammal remains. Quaternary International. 2012: 276-277: 145-154.\n'},{id:"B43",body:'\nCorcho Alvarado, J.A., Leuenberger, M., Kipfer, R., Paces, T., Purtschert, R. Reconstruction of past climate conditions over central Europe from groundwater data. Quaternary Science Reviews. 2011: 30: 3423-3429.\n'},{id:"B44",body:'\nHuang, Y., Street-Perrott, F.A., Metcalfe, S.E., Brenner, M., Moreland, M., Freeman, K.H. Climate change as the dominant control on glacialinterglacial variations in C3 and C4 plant abundance. Science. 2001: 293: 1647-1651.\n'},{id:"B45",body:'\nHall, S.A., Penner, W.L. Stable carbon isotopes, C3-C4 vegetation, and 12 800 years of climate change in central New Mexico, USA. Palaeogeography, Palaeoclimatology, Palaeoecology. 2013: 369: 272-281.\n'},{id:"B46",body:'\nGaly, V., François, L., France-Lanord, C., Faure, P., Kudrass, H., Palhol, F., Singh, S.K. C4 plants decline in the Himalayan basin since the Last Glacial Maximum. Quaternary Science Reviews. 2008: 27: 1396-1409.\n'},{id:"B47",body:'\nSümegi, P., Gulyás, S., Persaits, G., Szelepcsényi, Z. In: Rakonczai, János, Ladányi, Zsuzsanna (Eds.), Long Environment Change in the Forest Steppe Habitat of the Great Hungarian Plain Based on Palaeoecoloical Data. Review of Climate Change Research Program at the University of Szeged (2010-2012). Institute of Geography and Geology, 09/2012: 7-24p.\n'},{id:"B48",body:'\nSchatz, A.-K., Zech, M., Buggle, B., Gulyás, S., Hambach, U., Marković, S.B., Sümegi, P., Scholten, T. The late Quaternary loess record of Tokaj, Hungary: reconstructing palaeoenvironment, vegetation and climate using stable C and N isotopes and biomarkers. Quaternary International. 2011: 240: 52-61.\n'},{id:"B49",body:'\nAmbrose, S.H., Sikes, N.E. Soil carbon isotope evidence for Holocene habitat change in the Kenya Rift Valley. Science. 1991: 253 (5026): 1402-1405.\n'},{id:"B50",body:'\nMcConnaughey, T.A., Gilikin, D.P. Carbon isotopes in mollusc shell carbonates. Geo-Marine Letters. 2008: 28: 287-299.\n'},{id:"B51",body:'\nBar-Yosef, O., Pilbeam, D. Peabody Museum Bulletin 8, Harvard University, Cambridge. 2000.\n'},{id:"B52",body:'\nBolus, M., Conard, N.J. The late Middle Paleolithic and earlies Upper Paleolithic in Central Europe and their relevance for the Out of Africa hypothesis. In: Straus, L., Bar-Yosef, O. (Eds.), Out of Africa in the Pleistocene, vol. 75. Quaternary International. 2001: 29-40.\n'},{id:"B53",body:'\nJelínek, J. Neanderthal remains in Kůlna Cave, Czechoslovakia. In: Schwidetzky, I., Chiarelli, B., Nekrasov, O. (Eds.), Physical Anthropology of European Populations. Mouton, 1980: The Hague. 351-353.\n'},{id:"B54",body:'\nWolpoff, M.H., Smith, F.H., Malez, M., Radovčić, J., Rukavina, D. Upper Pleistocene human remains from Vindija Cave, Croatia, Yugoslavia. American Journal of Physical Anthropology. 1981: 54, 499-545.\n'},{id:"B55",body:'\nSmith, F.H. Upper Pleistocene hominid evolution in South–Central Europe: a review of the evidence and analysis of trends. Current Anthropology. 1982: 23: 667-686.\n'},{id:"B56",body:'\nRink, W.J., Schwarcz, H.P., Smith, F.H., Radovčić, J. ESR ages for Krapina hominids. Nature. 1995: 378, 24.\n'},{id:"B57",body:'\nKaravanič, I., Smith, F.H. The Middle/Upper Paleolithic interface and the relationship of Neanderthals and early modern humans in the Hrvatsko Zagorje, Croatia. Journal of Human Evolution. 1998: 34: 223-248.\n'},{id:"B58",body:'\nAhern, J.C.M., Karavanič, I., Paunović, M., Janković, I., Smith, F.J. New discoveries and interpretations of hominid fossils and artifacts from Vindija Cave, Croatia. Journal of Human Evolution. 2004: 46: 25-65.\n'},{id:"B59",body:'\nKrings, M., Capelli, C., Tschentscher, F., Geisart, H., Meyer, S., von Haeseler, A., Grossschmidt, K., Possnert, G., Paunović, M., Pääbo, S., 2000. A view of Neanderthal genetic diversity. Nat. Genet. 26, 144-146.\n'},{id:"B60",body:'\nSmith, F.H., Trinkaus, E., Pettitt, P.B., Karavanič, I., Paunović, M. Direct radiocarbon dates for Vindija G1 and Velika Pećina Late Pleistocene hominid remains. Proceedings of the National Academy of Science. 1999: 96: 12281-12286.\n'},{id:"B61",body:'\nMellars, P. Archeology and the Dispersal of Modern Humans in Europe: Deconstructing the Aurignacian. Evolutionary Anthropology. 2006: 15: 167-182.\n'},{id:"B62",body:'\nMester, Z. The problems of the Szeletian as seen from Hungary. Recherches Archéologiques. 2017: NS9: 19-48.\n'},{id:"B63",body:'\nZilhão, J., d’Errico, F. The Neanderthal Problem Continued: Reply. Current Anthropology. 1999: 40: 355-364.\n'},{id:"B64",body:'\nSvoboda, J. Mladeč and other caves in the Middle Danube region: early modern humans, late Neandertals, and projectiles. In: Les premiers hommes modernes de la Péninsule Ibérique. Actes du Colloque de la Commission VIII de l’UISPP. IPA, 2001b: Lisbon. 45-60.\n'},{id:"B65",body:'\nMiracle, P. The spread of modernity in Paleolithic Europe. In: Omoto, K., Tobias, P. (Eds.), The Origins and Past of Modern Humans—Towards Reconciliation. Recent Advances in Modern Biology. 1998: vol. 3. World Scientific Publishing, Singapore, 171-187.\n'},{id:"B66",body:'\nGaábori-Csánk, V. Le Jankovichien. Une civilisation paléolithique en Hongrie. 1994: ERAUL 53, Liége.\n'},{id:"B67",body:'\nSefcakova, A. Pleistocene anthropological finds from the territory of Slovakia. Acta Rer. Natur. Mus. Nat. Slov., 2007. Vol. LIII, 26-45.\n'},{id:"B68",body:'\nSvoboda, J., Ložek, V., Vlček, E. Hunters Between East and West. The Paleolithic of Moravia. 1996: Plenum, London, NY.\n'},{id:"B69",body:'\nSvoboda, J., Škrdla, P. The Bohunician technology. In: Dibble, H.L., Bar-Yosef, O. (Eds.), The Definition and Interpretation of Levallois Technology. Prehistory Press, Madison, 1995: 429-438.\n'},{id:"B70",body:'\nSchmitz, R. W., D. Serre, G. Bonani, S. Feine, F. Hillgruber, H. Krainitzki, S. Pääbo and F. H. Smith. The Neandertal type site revisited: Interdisciplinary investigations of skeletal remains from the Neander Valley, Germany. Proceedings of the National Academy of Sciences 2002: 99, 13342-13347.\n'},{id:"B71",body:'\nTrinkaus, E., Milota, Ş., Rodrigo, R., Mircea, G., Moldovan, O. Early Modern Human Cranial Remains from the Pestera çu Oase, Romania. Journal of Human Evolution 2003a: 45: 245-253.\n'},{id:"B72",body:'\nHaesaerts, P., Damblon, F., Bachner, M., Trnka, G. Revised stratigraphy and chronology of the Willendorf II sequence, Lower Austria. Archaeologia Austriaca 1996: 80: 25-42.\n'},{id:"B73",body:'\nBolus, M., Conard, N.J. The late Middle Paleolithic and earliest Upper Paleolithic in Central Europe and their relevance for the Out of Africa hypothesis. In: Straus, L., Bar-Yosef, O. (Eds.), Out of Africa in the Pleistocene. Quaternary International, 2001: 75: 29-40.\n'},{id:"B74",body:'\n\nThomas, H., Basell, L., Jacobic, R., Wood, R., Bronk Ramsey, C., Conard. N.J. Τesting models for the beginnings of the Aurignacian and the advent of figurative art and music: The radiocarbon chronology of Geißenklösterle. Journal of Human Evolution. 2012: 62 (6): 664-676.\n'},{id:"B75",body:'\nChurchill S.E., Franciscus R.G., McKean-Peraza H.A., Daniel J.A., Warren B.R. Shanidar 3 Neandertal rib puncture wound and paleolithic weaponry. Journal of Human Evolution, 2009;57: 163-78.\n'},{id:"B76",body:'\nGreenbaum, G; Getz, W. M.; Rosenberg, N. A.; Feldman, M. W.; Hovers, E.; Kolodny, O. Disease transmission and introgression can explain the long-lasting contact zone of modern humans and Neanderthals. Nature Communications. 2019: 10 (1): 5003.\n'},{id:"B77",body:'\nPearce, E., Stringer, C., Dunbar R.I.M. New insights into differences in brain organization between Neanderthals and anatomically modern humans. Proceedings of Biological Sciences, 2013: 280: Issue 1758.\n'},{id:"B78",body:'\nGolovanova, L.V.; Doronichev, V.B.; Cleghorn, N.E.; Koulkova, M.A.; Sapelko, T.V.; Shackley, M.S. Significance of Ecological Factors in the Middle to Upper Paleolithic Transition. Current Anthropology. 2010: 51 (5): 655-691.\n'},{id:"B79",body:'\nHigham, T., Douka, K., Wood, R. et al. The timing and spatiotemporal patterning of Neanderthal disappearance. Nature 2014: 512, 306-309.\n'},{id:"B80",body:'\nHigham, T. European Middle and Upper Palaeolithic radiocarbon dates are often older than they look: problems with previous dates and some remedies. Antiquity 2011: 85, 235-249.\n'},{id:"B81",body:'\nAlexandrowicz W.P. Malacological sequence of Weichselian (MIS 5-2) loess series from a profile in Grodzisko Dolne (southern Poland) and its palaeogeographic significance. Quaternary International. 2014: 319: 109-118.\n'}],footnotes:[],contributors:[{corresp:"yes",contributorFullName:"Adriano Banak",address:"abanak@hgi-cgs.hr",affiliation:'
Department of Geology, Croatian Geological Survey, Croatia
Institute for Coastal Marine Environment (IAMC), INRC, Italy
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O. R. 2000-2006, misura 3.16). \r\n•2004 – 2005 Responsible for the project “Tolerance of cereals to nutritional and salinity stresses: role of nitrate in regulation of compatible solutes biosynthesisâ€. L.R.5/02- annualità 2002.\r\n•2004 - 2005 Lecturer of Plant Cultures and Biotechnological Applications at the Biotechnology Faculty of the Second University of Naples.\r\n•2004 – 2010 Referee for Journal of Agricultural and Food Chemistry \r\n•2005 - 2010 Member of the PhD School in “Resources and Environmentâ€\r\n•2006 – 2010 Lecturer of Ecophysiology and Applications at the Science Faculty of the Second University of Naples.\r\n•2007 – 2010 Referee for New Phytologist \r\n•2007 – 2010 Lecturer of General Biology at the Pharmacy Faculty of the Second University of Naples.\r\n•2007 – 2010 Organiser of the Erasmus-Socrates program for the Courses of Study in Biology at the Second University of Naples \r\n•2008 – 2009 Responsible for the project “Sulphur nutrition and salt stress in durum wheat plantsâ€. L.R.5/02- annualità 2006.\r\n•2008 – 2010 Referee for European projects \r\n•2010 – Professorship (associate professor) of Plant Physiology \r\nThe research interests of Petronia Carillo are primarily centred on the interactions between nitrogen assimilation and carbon metabolism, and their short-term and long-term control mechanisms in photosynthetic organisms (unicellular algae and plants).\r\nAt present, the main focus is metabolite profiling of durum wheat, maize and potato under salt and water stress.\r\nAs visiting scientist of Max-Planck-Institute for Molecular Plant Physiolgy of Potsdam (Germany), Dr. Carillo has been involved in the development of i) new high-throughput methods to measure enzyme activities and metabolites in plants using a robot-based platform, and ii) enzymatic and mass-spectrometric methods for the determination of trehalose 6-phosphate and trehalose in plants.\r\nSignificant publications:\r\n1.- STITT M., MüLLER C., MATT P., GIBON Y., Carillo P., MORCUENDE R., SCHEIBLE W-R. and KRAPP A. 2002 - Steps towards an integrated view of nitrogen metabolism. Journal of Experimental Botany. 53(370): 959-970. \r\n\r\n2.- YVES GIBON, OLIVER E. BLAESING, JAN HANNEMANN, PETRONIA CARILLO, MELANIE HOEHNE, JANNEKE H.M. HENDRIKS, NATALIA PALACIOS-ROJAS, JOANNA CROSS, JOACHIM SELBIG, AND MARK STITT 2004 - A Robot-Based Platform to Measure Multiple Enzyme Activities in Arabidopsis Using a Set of Cycling Assays: Comparison of Changes of Enzyme Activities and Transcript Levels during Diurnal Cycles and Prolonged Darkness. Plant Cell 16: 3304-3325. \r\n\r\n3.- CARILLO, P.; MASTROLONARDO, G.; NACCA, F. AND FUGGI A 2005. Nitrate reductase in durum wheat seedlings as affected by nitrate nutrition and salinity. Functional Plant Biology 32 (3), 209-219.\r\n\r\n4.- LUNN J.E., FEIL R., HENDRIKS J.H.M., GIBON Y., MORCUENDE R., OSUNA D., SCHEIBLE W-R., CARILLO P., HAJIREZAEI M-R. AND STITT M. 2006 - Sugar-induced increases in trehalose 6-phosphate are correlated with redox activation of ADPglucose pyrophosphorylase and higher rates of starch synthesis in Arabidopsis thaliana. Biochemical Journal 397: 139-148.\r\n\r\n5.- DI MARTINO RIGANO V., VONA V., LOBOSCO O., CARILLO P., LUNN J.E., CARFAGNA S. ESPOSITO S., CAIAZZO M. AND RIGANO C. 2006 - Temperature dependence of nitrate reductase in the psychrophilic unicellular alga Koliella antarctica and mesophilic alga Chlorella sorokiniana. Plant, Cell and Environment 29: 1400-1409. \r\n\r\n6.- MAGGIO A.; CARILLO P., BULMETTI G.S., FUGGI A., BARBIERI G., DE PASCALE S. 2008 Potato yield and metabolic profiling under conventional and organic farming. European Journal of Agronomy 28(3): 343-350. \r\n\r\n7.- SIENKIEWICZ-PORZUCEK A., NUNES-NESI A., SULPICE R., LISEC J, CENTENO D.C., CARILLO P., LEISSE A., URBANCZYK-WOCHNIAK E., FERNIE A.R. 2008 Mild reductions in mitochondrial citrate synthase activity result in a compromised nitrate assimilation and reduced leaf pigmentation but have no effect on photosynthetic performance or growth. Plant Physiology 147: 115-127 doi:10.1104/pp.108.117978.\r\n\r\n8.- CARILLO, P., MASTROLONARDO, G., NACCA, F., PARISI D., VERLOTTA A. AND FUGGI A. 2008 Nitrogen metabolism in durum wheat under salinity: accumulation of proline and glycine betaine. Functional Plant Biology 35 (5), 412-426.\r\n\r\n9.- CARILLO P., CACACE D, DE ROSA M., DE MARTINO E., COZZOLINO C., NACCA F., D’ANTONIO R., FUGGI A. 2009 Process optimization and physicochemical characterization of potato powder Int. J. Food Sci. Technol. 44 (1), 145-151\r\n\r\n10.- TSCHOEP H., GIBON Y., CARILLO P., ARMENGAUD P., SZECOWKA M., NUNES-NESI A., FERNIE A.R., KOEHL K. AND STITT M. 2009 Adjustment of Growth and Central Metabolism to a Mild but Sustained Nitrogen-Limitation in Arabidopsis. Plant Cell Environ 32 (3), 300-318.\r\n\r\n11.- CARILLO P., COZZOLINO C., D’ABROSCA B., NACCA F., DELLAGRECA M., FIORENTINO A., FUGGI A. 2010 Effects of the allelochemicals dihydrodiconiferyl alcohol and lariciresinol on metabolism of Lactuca sativa . The Open Bioactive Compounds Journal. 3, 18-24.\r\n\r\n12.- WOODROW P., PONTECORVO G., FANTACCIONE S., FUGGI A., KAFANTARIS I., PARISI D., CARILLO P. 2010 Polymorphism of a new Ty1-copia retrotransposon in durum wheat under salt and light stresses. Theor Appl Genet. 121(2), 311-22.\r\n\r\n13. WOODROW P., PONTECORVO G., CIARMIELLO LF., FUGGI A., CARILLO P. 2010 Ttd1a promoter is involved in DNA-protein binding by salt and light stresses. Molecular Biology Reports (in press). DOI: 10.1007/s11033-010-0494-3.\r\n\r\n14.- CARILLO P., PARISI D., WOODROW P., PONTECORVO G., MASSARO G., ANNUNZIATA MG., FUGGI A. (2010) Salt induced accumulation of glycine betaine is inhibited by high light in Durum wheat. Functional Plant Biology (accepted).",institutionString:null,institution:{name:'University of Campania "Luigi Vanvitelli"',institutionURL:null,country:{name:"Italy"}}},{id:"47808",title:"Prof.",name:"Amodio",surname:"Fuggi",slug:"amodio-fuggi",fullName:"Amodio Fuggi",position:null,profilePictureURL:"//cdnintech.com/web/frontend/www/assets/author.svg",biography:null,institutionString:null,institution:{name:'University of Campania "Luigi Vanvitelli"',institutionURL:null,country:{name:"Italy"}}},{id:"47809",title:"Dr.",name:"Maria Grazia",surname:"Annunziata",slug:"maria-grazia-annunziata",fullName:"Maria Grazia Annunziata",position:null,profilePictureURL:"//cdnintech.com/web/frontend/www/assets/author.svg",biography:null,institutionString:null,institution:null},{id:"48052",title:"Dr.",name:"Mark",surname:"Hodges",slug:"mark-hodges",fullName:"Mark Hodges",position:null,profilePictureURL:"//cdnintech.com/web/frontend/www/assets/author.svg",biography:null,institutionString:null,institution:null},{id:"51845",title:"Dr.",name:"Peter",surname:"Toivonen",slug:"peter-toivonen",fullName:"Peter Toivonen",position:null,profilePictureURL:"//cdnintech.com/web/frontend/www/assets/author.svg",biography:null,institutionString:null,institution:null},{id:"56133",title:"Prof.",name:"Chengcai",surname:"Chu",slug:"chengcai-chu",fullName:"Chengcai Chu",position:null,profilePictureURL:"//cdnintech.com/web/frontend/www/assets/author.svg",biography:null,institutionString:null,institution:{name:"Chinese Academy of Sciences",institutionURL:null,country:{name:"China"}}},{id:"59510",title:"Dr.",name:"Elena",surname:"Degl'Innocenti",slug:"elena-degl'innocenti",fullName:"Elena Degl'Innocenti",position:null,profilePictureURL:"//cdnintech.com/web/frontend/www/assets/author.svg",biography:null,institutionString:null,institution:null}]},generic:{page:{slug:"our-story",title:"Our story",intro:"
The company was founded in Vienna in 2004 by Alex Lazinica and Vedran Kordic, two PhD students researching robotics. While completing our PhDs, we found it difficult to access the research we needed. So, we decided to create a new Open Access publisher. A better one, where researchers like us could find the information they needed easily. The result is IntechOpen, an Open Access publisher that puts the academic needs of the researchers before the business interests of publishers.
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We started by publishing journals and books from the fields of science we were most familiar with - AI, robotics, manufacturing and operations research. Through our growing network of institutions and authors, we soon expanded into related fields like environmental engineering, nanotechnology, computer science, renewable energy and electrical engineering, Today, we are the world’s largest Open Access publisher of scientific research, with over 4,200 books and 54,000 scientific works including peer-reviewed content from more than 116,000 scientists spanning 161 countries. Our authors range from globally-renowned Nobel Prize winners to up-and-coming researchers at the cutting edge of scientific discovery.
\\n\\n
In the same year that IntechOpen was founded, we launched what was at the time the first ever Open Access, peer-reviewed journal in its field: the International Journal of Advanced Robotic Systems (IJARS).
\\n\\n
The IntechOpen timeline
\\n\\n
2004
\\n\\n
\\n\\t
Intech Open is founded in Vienna, Austria, by Alex Lazinica and Vedran Kordic, two PhD students, and their first Open Access journals and books are published.
\\n\\t
Alex and Vedran launch the first Open Access, peer-reviewed robotics journal and IntechOpen’s flagship publication, the International Journal of Advanced Robotic Systems (IJARS).
\\n
\\n\\n
2005
\\n\\n
\\n\\t
IntechOpen publishes its first Open Access book: Cutting Edge Robotics.
\\n
\\n\\n
2006
\\n\\n
\\n\\t
IntechOpen publishes a special issue of IJARS, featuring contributions from NASA scientists regarding the Mars Exploration Rover missions.
\\n
\\n\\n
2008
\\n\\n
\\n\\t
Downloads milestone: 200,000 downloads reached
\\n
\\n\\n
2009
\\n\\n
\\n\\t
Publishing milestone: the first 100 Open Access STM books are published
\\n
\\n\\n
2010
\\n\\n
\\n\\t
Downloads milestone: one million downloads reached
\\n\\t
IntechOpen expands its book publishing into a new field: medicine.
\\n
\\n\\n
2011
\\n\\n
\\n\\t
Publishing milestone: More than five million downloads reached
\\n\\t
IntechOpen publishes 1996 Nobel Prize in Chemistry winner Harold W. Kroto’s “Strategies to Successfully Cross-Link Carbon Nanotubes”. Find it here.
\\n\\t
IntechOpen and TBI collaborate on a project to explore the changing needs of researchers and the evolving ways that they discover, publish and exchange information. The result is the survey “Author Attitudes Towards Open Access Publishing: A Market Research Program”.
\\n\\t
IntechOpen hosts SHOW - Share Open Access Worldwide; a series of lectures, debates, round-tables and events to bring people together in discussion of open source principles, intellectual property, content licensing innovations, remixed and shared culture and free knowledge.
\\n
\\n\\n
2012
\\n\\n
\\n\\t
Publishing milestone: 10 million downloads reached
\\n\\t
IntechOpen holds Interact2012, a free series of workshops held by figureheads of the scientific community including Professor Hiroshi Ishiguro, director of the Intelligent Robotics Laboratory, who took the audience through some of the most impressive human-robot interactions observed in his lab.
\\n
\\n\\n
2013
\\n\\n
\\n\\t
IntechOpen joins the Committee on Publication Ethics (COPE) as part of a commitment to guaranteeing the highest standards of publishing.
\\n
\\n\\n
2014
\\n\\n
\\n\\t
IntechOpen turns 10, with more than 30 million downloads to date.
\\n\\t
IntechOpen appoints its first Regional Representatives - members of the team situated around the world dedicated to increasing the visibility of our authors’ published work within their local scientific communities.
\\n
\\n\\n
2015
\\n\\n
\\n\\t
Downloads milestone: More than 70 million downloads reached, more than doubling since the previous year.
\\n\\t
Publishing milestone: IntechOpen publishes its 2,500th book and 40,000th Open Access chapter, reaching 20,000 citations in Thomson Reuters ISI Web of Science.
\\n\\t
40 IntechOpen authors are included in the top one per cent of the world’s most-cited researchers.
\\n\\t
Thomson Reuters’ ISI Web of Science Book Citation Index begins indexing IntechOpen’s books in its database.
\\n
\\n\\n
2016
\\n\\n
\\n\\t
IntechOpen is identified as a world leader in Simba Information’s Open Access Book Publishing 2016-2020 report and forecast. IntechOpen came in as the world’s largest Open Access book publisher by title count.
\\n
\\n\\n
2017
\\n\\n
\\n\\t
Downloads milestone: IntechOpen reaches more than 100 million downloads
\\n\\t
Publishing milestone: IntechOpen publishes its 3,000th Open Access book, making it the largest Open Access book collection in the world
We started by publishing journals and books from the fields of science we were most familiar with - AI, robotics, manufacturing and operations research. Through our growing network of institutions and authors, we soon expanded into related fields like environmental engineering, nanotechnology, computer science, renewable energy and electrical engineering, Today, we are the world’s largest Open Access publisher of scientific research, with over 4,200 books and 54,000 scientific works including peer-reviewed content from more than 116,000 scientists spanning 161 countries. Our authors range from globally-renowned Nobel Prize winners to up-and-coming researchers at the cutting edge of scientific discovery.
\n\n
In the same year that IntechOpen was founded, we launched what was at the time the first ever Open Access, peer-reviewed journal in its field: the International Journal of Advanced Robotic Systems (IJARS).
\n\n
The IntechOpen timeline
\n\n
2004
\n\n
\n\t
Intech Open is founded in Vienna, Austria, by Alex Lazinica and Vedran Kordic, two PhD students, and their first Open Access journals and books are published.
\n\t
Alex and Vedran launch the first Open Access, peer-reviewed robotics journal and IntechOpen’s flagship publication, the International Journal of Advanced Robotic Systems (IJARS).
\n
\n\n
2005
\n\n
\n\t
IntechOpen publishes its first Open Access book: Cutting Edge Robotics.
\n
\n\n
2006
\n\n
\n\t
IntechOpen publishes a special issue of IJARS, featuring contributions from NASA scientists regarding the Mars Exploration Rover missions.
\n
\n\n
2008
\n\n
\n\t
Downloads milestone: 200,000 downloads reached
\n
\n\n
2009
\n\n
\n\t
Publishing milestone: the first 100 Open Access STM books are published
\n
\n\n
2010
\n\n
\n\t
Downloads milestone: one million downloads reached
\n\t
IntechOpen expands its book publishing into a new field: medicine.
\n
\n\n
2011
\n\n
\n\t
Publishing milestone: More than five million downloads reached
\n\t
IntechOpen publishes 1996 Nobel Prize in Chemistry winner Harold W. Kroto’s “Strategies to Successfully Cross-Link Carbon Nanotubes”. Find it here.
\n\t
IntechOpen and TBI collaborate on a project to explore the changing needs of researchers and the evolving ways that they discover, publish and exchange information. The result is the survey “Author Attitudes Towards Open Access Publishing: A Market Research Program”.
\n\t
IntechOpen hosts SHOW - Share Open Access Worldwide; a series of lectures, debates, round-tables and events to bring people together in discussion of open source principles, intellectual property, content licensing innovations, remixed and shared culture and free knowledge.
\n
\n\n
2012
\n\n
\n\t
Publishing milestone: 10 million downloads reached
\n\t
IntechOpen holds Interact2012, a free series of workshops held by figureheads of the scientific community including Professor Hiroshi Ishiguro, director of the Intelligent Robotics Laboratory, who took the audience through some of the most impressive human-robot interactions observed in his lab.
\n
\n\n
2013
\n\n
\n\t
IntechOpen joins the Committee on Publication Ethics (COPE) as part of a commitment to guaranteeing the highest standards of publishing.
\n
\n\n
2014
\n\n
\n\t
IntechOpen turns 10, with more than 30 million downloads to date.
\n\t
IntechOpen appoints its first Regional Representatives - members of the team situated around the world dedicated to increasing the visibility of our authors’ published work within their local scientific communities.
\n
\n\n
2015
\n\n
\n\t
Downloads milestone: More than 70 million downloads reached, more than doubling since the previous year.
\n\t
Publishing milestone: IntechOpen publishes its 2,500th book and 40,000th Open Access chapter, reaching 20,000 citations in Thomson Reuters ISI Web of Science.
\n\t
40 IntechOpen authors are included in the top one per cent of the world’s most-cited researchers.
\n\t
Thomson Reuters’ ISI Web of Science Book Citation Index begins indexing IntechOpen’s books in its database.
\n
\n\n
2016
\n\n
\n\t
IntechOpen is identified as a world leader in Simba Information’s Open Access Book Publishing 2016-2020 report and forecast. IntechOpen came in as the world’s largest Open Access book publisher by title count.
\n
\n\n
2017
\n\n
\n\t
Downloads milestone: IntechOpen reaches more than 100 million downloads
\n\t
Publishing milestone: IntechOpen publishes its 3,000th Open Access book, making it the largest Open Access book collection in the world
\n
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