Theoretical study of the charge carrier mobilities of the molecular materials tetrathiafulvalene (TTF) and 2,5-bis(1,3-dithiolan-2-ylidene)-1,3,4,6-tetrathiapentalene (BDH-TTP)

Tetrathiafulvalene (TTF) is a kind of fused ring aromatic compound containing four sulfur atoms in one molecule, which is well known as a charge transport material. In order to calculate the charge mobility of this semiconductor, Marcus electron transfer theory and the embedded model, which can give small intramolecular reorganization energies, were employed. The calculated results were in good agreement with the experimental values, so the above computing model is appropriate to assess the electrical property of TTF. On this basis, we predicted the charge mobility of 2,5-bis(1,3-dithiolan-2-ylidene)-1,3,4,6-tetrathiapentalene (BDH-TTP) crystals, for which the molecular structure is similar to TTF. The calculated results indicated that BDH-TTP is a p-type material, which has a better performance than TTF in hole transfer due to larger hole coupling and the smaller hole injection barrier. In addition, the direct coupling (DC) and the site energy correction (SEC) methods were used to calculate the charge transfer integrals. Although the results were slightly different, the qualitative trends were the same. Furthermore we took into account the anisotropic transfer properties of TTF and BDH-TTF, since obviously the mobilities along one dimension are larger than those along three dimensions. Finally, natural bond orbital analysis was used to study the interactions in all of the dimers.     

Tuning delocalization in the radical cations of 1,4-bis[4-(diarylamino)styryl]benzenes, 2,5-bis[4-(diarylamino)styryl]thiophenes, and 2,5-bis[4-(diarylamino)styryl]pyrroles through substituent effects

Radical cations have been generated for 10 bis[4-(diarylamino)styryl]arenes and heteroarenes to investigate the effect of the electron-richness of the terminal groups and of the bridging (hetero)arene on delocalization. The intervalence charge-transfer bands of these radical cations vary from weak broad Gaussians, indicative of localized class-II mixed-valence species, to strong relatively narrow asymmetric bands, characteristic of delocalized class-III bis(diarylamino) species, to narrow symmetric bands in cases where the bridge contribution to the singly occupied molecular orbital is largest. Hush analysis of these bands yields estimates of the electronic coupling varying from 480 cm(-1) (electron-poor bridge, most electron-rich terminal aryl groups) to 1000 cm(-1) (electron-rich bridge, least electron-rich termini) if the diabatic electron-transfer distance, R(ab), is equated to the N-N separation. Computational and electron spin resonance (ESR) evidence for displacement of the diabatic states into the bridge (reduced R(ab)) suggests that these values are underestimates and that even more variation is to be expected through the series. Several dications have also been studied. The vis-NIR absorption of the dication of (E,E)-1,4-bis{4-[bis(4-n-butoxyphenyl)amino]styryl}-2,5-dicyanobenzene is seen at an energy similar to that of the strongest band in the spectrum of the corresponding weakly coupled monocation, with approximately twice the absorptivity, and its ESR spectrum suggests essentially noninteracting radical centers. In contrast, the electronic spectra of class-III monocations show no clear relationship to those of the corresponding dications, which ESR reveals to be singlet species.     

Structures of substituted di-aryl-1,3,4-oxadiazole derivatives: 2,5-bis(pyridyl)- and 2,5-bis(aminophenyl)-substitution

Crystal structures of four different di-aryl-1,3,4-oxadiazole compounds (aryl = 2-pyridyl-, 3-pyridyl-, 2-aminophenyl-, 3-aminophenyl-) are determined. Crystallization of di(2-pyridyl)-1,3,4-oxadiazole yielded monoclinic and triclinic polymorphs. The structures are characterized by the occurrence of π–π interactions. Additionally, in case of the aminophenyl compounds intra- as well as intermolecular hydrogen bonds are found that influence the packing motif as well. Since these molecules are often used as ligands in metal–organic complexes similarities and differences of the molecular conformation between the molecules in the pure crystals and that of the ligands in the complexes are discussed.     

Theoretical study on the substituent effect of a Wittig reaction

The substituent effects of F, H and methyl (Me) in replacement of phenyl (Ph) groups bonding with the ylide phosphorus in Wittig reactions have been examined theoretically by performing ab intio calculations. It is shown that the energy barrier for the Wittig reaction with F as the substituent is much higher than that with H, Me and Ph. The Wittig reaction is found to be more favorable with the substituent in the order F<H<Ph<Me. The reactions are found to proceed through two transition states: the formation and the decomposition of oxaphosphetane. We conclude that only the model of the Wittig reaction in which Ph is simplified to Me can reasonably describe the real Wittig reaction. Received: 7 August 2001 / Accepted: 25 October 2001 / Published online: 22 March 2002     

2,5-bis(trifluoromethyl)-1,3,4-oxadiazole in cycloaddition reactions

The cycloaddition of 2,5-bis(trifluoromethyl)-1,3,4-oxadiazole to dienophiles with cyclic and acyclic structures takes place according to a two-step mechanism with the extrusion of nitrogen and results in the formation of derivatives of 7-oxabicyclo [2.2.1]heptanes. A significant influence of the donor properties of the dienophiles, as well as of the spatial factors, on the realization of these processes has been discovered. However, solvation efects do not have a significant effect on the formation of the cycloadducts. The regio- and stereoselectivity of the cyclo-addition reactions has been noted.For a preliminary report, see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 95–100, January, 1990.     

Ether Fission of 2,5-bis(Dialkylamino)hydroquinone Dimethylethers and O-Alkylation of 2,5-bis(Dialkylamino)hydroquinones

In connection with work underway in these laboratories on the total synthesis of Pentacyciic. triterpenes; guitable methods were sought for the introduction of angular methyl groups into preiormed polynuclear systems. A method of some generality was recognized in the work ofNagata³ on the organoaluminum catalyzed conjugate addition of cyanide to α,β-unsaturated ketones and subsequent conversion of the resulting cyano group to the desired angular methyl substttuent. The total synthesis of dl-alnusenone reported^4a earlier from these laboratories has this synthon as its central feature. Another approach that appeared attractive entailed the 1,6-addition ⁵ of cyanide to the dienone 1, available from intermediates already in hand.^4b     

Synthesis, structure, aggregation-induced emission, self-assembly, and electron mobility of 2,5-bis(triphenylsilylethynyl)-3,4-diphenylsiloles

2,5-Bis(triphenylsilylethynyl)-3,4-diphenylsiloles with different 1,1-substituents [XYSi(CPh)(2) (C-C≡C-SiPh(3))(2)] (Ph=phenyl) were synthesized in high yields by the Sonogashira coupling of 2,5-dibromo-3,4-diphenylsiloles with triphenylsilylacetylene, and two of these were characterized crystallographically. Crystal structures and theoretical calculations showed that the new silole molecules had higher conjugation than 2,5-diarylsiloles. They possessed low HOMO and LUMO energy levels due to the electron-withdrawing effect of the triphenylsilylethynyl groups. Cyclic voltammetry analysis revealed low electron affinities, which were comparable to those of perfluoroarylsiloles. B3LYP/6-31* calculations demonstrated that the new siloles possessed large reorganization energies for electron and hole transfers and high electron mobilities. A mobility of up to 1.2×10(-5) cm(2) V(-1) s(-1) was obtained by the transient electroluminescence method, which was about fivefold higher than that of tris(8-hydroxyquinolinato)aluminum, a widely used electron-transport material, under the same conditions. All of the silole molecules possessed high thermal stability. Although, their solutions were weakly emissive, their nanoparticle suspensions and thin films emitted intense blue-green light upon photoexcitation, demonstrating a novel feature of aggregation-induced emission (AIE). Polarized emissions were observed in the silole crystals. The addition of solvents, which did not dissolve the silole molecules, into silole-containing solutions caused self-assembly of the molecules, which produced macroscopic fibrils with strong light emissions.     

Polyhydrazides based on 2,5-bis(4-carboxymethylene phenyl)-3,4-diphenyl thiophene

A series of polyhydrazides was synthesized from a novel dicarboxylic acid, 2,5-bis(4-carboxymethylene phenyl)-3,4-diphenyl thiophene (V) and or terephthalic acid and isophthaloyl or terephthaloyl dihydrazide by Yamazaki’s phosphorylation method using triphenyl phosphite as condensing agent. Polyhydrazides were characterized by IR spectroscopy solubility, viscosity, thermogravimetric analysis and X-ray diffraction studies.The polymers were obtained in quantitative yields. Polyhydrazides had viscosities in the range of 0.25-0.70 dL/g. The polymers derived from novel diacid (V) showed enhanced solubility than the polymers derived from terephthalic acid, which may be attributed to the presence to bulky pendant phenyl group and methylene spacer group in the polymer backbone. Polymers were soluble in most of the common aprotic polar solvents. Polyhydrazides showed considerable weight loss in the temperature range of 300-400 °C which is due to the cyclodehydration, leading to the formation of corresponding polyoxadiazoles. They showed T_max in between 500 and 600 °C which is essentially the decomposition of the polyoxadiazoles. X-ray diffraction studies showed that polyhydrazides were amorphous in nature.     

Theoretical study on photophysical and charge transport properties of 1,6-bis(2-hydroxyphenol)pyridylboron bis(4-n-butylphenyl)phenyleneamine compound

The absorption and emission spectra of 1,6-bis(2-hydroxyphenol)pyridylboron bis(4-n-butylphenyl)phenyleneamine were systematically calculated by time-dependent density functional theory (TD-DFT) level. These results are in good agreement with experiment ones. The charge transport properties were investigated within the framework of the charge hopping model. The results show that 1,6-bis(2-hydroxyphenyl)pyridineboron ((dppy)BF) functions as a electron transport group and triphenylamine as a hole transport group; the charge transport ability for the two types of carriers is not only high but also nearly balanced, which explains why it is an efficient single-layer electroluminescent device. On the basis of the large second-order polarizability value and high transparency, this compound has the possibility to be an excellent second-order nonlinear optical material. The main origin of this large second-order nonlinear optical response is charge transfer from the triphenylamine group to (dppy)BF.     

Crystal and molecular structure of 2,5-bis(fluorodinitromethyl)-1,3,4-oxadiazole

An X-ray structural study of 2,5-bis(fluorodinitromethyl)-1,3,4-oxadiazole (1), one of the representatives of azoles with strong electron-withdrawing substituents, has been carried out. It has been found that in the orthorhombic modification of1 the conformations of the fluorodinitromethyl groups are different. Intermolecular contacts in the crystal are realized through the heterocycles arranged at large angles to each other. The presence of strong electron-withdrawing substituents results in shortening of the C-O bonds and in a certain increase in the OCN angle in the 1,3,4-oxadiazole ring.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 639–641, April, 1994.     

Reaction of dimethylphosphorous acid with 2,5-bis(carbomethoxy)-3,4-diphenylcyclopentadienone

Conclusions The reaction of 2,5-bis(carbomethoxy)-3,4-diphenylcyclopentadienone with dimethyl phosphite, both in the presence of Et₃N and in the absence of catalysts, goes with the formation of the dimethyl esters of 2-oxo-4,5-diphenyl-1,3-dicarbomethoxy-4-cyclopentene- and 2-oxo-4,5-diphenyl-1,3-dicarbomethoxy-3-cyclopentene-1-phosphonic acids. In contrast to alcohols and primary amines, dimethyl phosphite does not form the 1,4-addition products with this acceptor.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 5, pp. 1119–1125, May, 1980.     

Synthesis of 2,5-bis(piperidinomethyl)piperidine and 1,5-bis(aminomethyl)-3-azabicyclo[3.2.1]octanones

Schmidt reaction of mono- and bis-Mannich bases1 and2 c derived from cyclopentanone gave the corresponding basically substituted 2-piperidones3 and4, respectively. Reduction of the latter afforded5. DoubleMannich reaction of2 a–c with primary amines gave 3-azabicyclo[3.2.1]octanone derivatives6 a–e and7. The transamination of2 a was investigated.     

Symmetrical mesogenic 2,5-bis(6-naphthalen-2-yl)-1,3,4-thiadiazoles

Two series of new symmetrical 1,3,4-oxadiazoles 1a-n and 1,3,4-thiadiazoles 1b-n were prepared and their mesomorphic properties investigated by optical microscopy, differential scanning calorimetry, and powder X-ray diffractometry. Compounds 1b-n are kinetically more stable than compounds 1a-n. Compounds 1a-n exhibited monotropic nematic or smectic C phases, whereas, compounds 1b-n exhibited enantiotropic nematic or smectic A/smectic C phases. Compounds 1b-n have higher clearing temperatures and the larger temperature ranges of mesophases, which might be attributed to the better linearity and/or larger dipole, resulted from a more polarized sulfur atom than oxygen atom incorporated. The fluorescent properties of these two series of 1,3,4-thiadiazole/oxadiazole-based derivatives were also examined. The λ_max peaks of the photoluminescence spectra for compounds 1a-6 and 1b-6 measured in THF occurred at ca. 385 nm and 423 nm, respectively. Both series were blue emitters.     

Catalytic hydrogenation of 2,5-bis(p-nitrophenyl)pyrimidine

We have studied the catalytic hydrogenation of 2,5-bis(p-nitrophenyl)pyrimidine over palladium on carbon under different conditions. We have established that hydrogenation in acetic acid at atmospheric hydrogen pressure leads to formation of 2,5-bis(p-aminophenyl)-1,4,5,6-tetrahydropyrimidine. Upon hydrogenation under pressure in DMF, along with 2,5-bis(p-aminophenyl)pyrimidiine, three isomeric (aminophenyl)pyrimidyl-substituted benzenes are formed as by-products. The mixture of these arylazo derivatives can be smoothly reduced by hydrogen under pressure in the presence of Raney nickel to bis(aminophenyl)pyrimidine.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1534–1539, November, 1993.We would like to acknowledge V.I. Mamatyuk and M. M. Shakirov for helping record and interpret the PMR spectra.     

Synthesis of N-methyl-2,5-bis(Trifluoromethyl)pyrroles

Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 6, p. 1445, June, 1989.