Barriers to conformational transformations in symmetrical linear conjugated systems

A quantum-chemical study has been carried out on conformational transformations in the ground and first excited states of symmetrical polymethine dyes and related α, ω-disubstituted polyenes. The magnitude of the trans-cis isomerization barriers depends on the length of the conjugation chain, position of the rotated bond, electron-donor capacity of the terminal groups, and occupancy of the electron shell. The rotation of molecular fragments in the excited state may lead to a change in the nature of the first electronic transition. Institute of Organic Chemistry, National Academy of Sciences of Ukraine, 5 Murmanskaya ul., Kiev 02094, Ukraine. Translated from Teoreticheskaya i éksperimental'naya Khimiya, Vol. 36, No. 3, pp. 162–168, May–June, 2000.     

Ab initio study of the ground state and conformational stability of peroxyacetyl nitrate in internal rotation about the peroxide bond

The molecular and electronic structure of the ground state of peroxyacetyl nitrate (PAN) was calculated by the unrestricted Hartree-Fock-Roothaan method with the use of the standard 3–21G and 6–31G basis set. The potential curve of the internal rotation about the peroxide bond of PAN was calculated with the 6–31G basis set. The curve contains two maxima. The ground state of PAN is characterized by a structure in which groups of atoms adjacent to the peroxide bond lie in planes that are perpendicular to each other (the dihedral angle ϱ(COON) is 89.9°). The calculated barriers to rotation are 19.6 and 66.8 kJ mol⁻¹. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 600–604, April, 1998.     

Physicochemical aspects of the creation of modern light-sensitive materials based on polymethine dyes

Features of the photophysical and photochemical characteristics of polymethine dyes that determine their use as light-sensitive materials (luminescent light concentrators, fluorescent probes and markers for the intercalation of DNA, laser media, polymerization photoinitiators, electroluminescent media) are analyzed. The main paths of the degradation of the electronic excitation energy (photoisomerization, intercombination and internal conversion, electron phototransfer in ion pairs, interaction of chromophores, like and mixed association) are discussed. The relation between these factors and the structure of the dyes and the nature of the medium is examined. Special attention is paid to methods of creating and optimizing colored light-sensitive polymeric materials. Institute of Organic Chemistry, National Academy of Sciences of Ukraine, 5 Murmanskaya ul., Kiev 253094. Translated from Teoreticheskaya i éksperimental'naya Khimiya, Vol. 34, No. 4, pp. 214–232, July–August, 1998.     

Charge distribution and 13C NMR spectra of cyanine dyes with bridging groupings in the chromophore

The electronic structure of cationoid and anionoid cyanine dyes was calculated by the CNDO/2 method. The calculation results were compared with the data of the ¹³C NMR spectra. It was shown that the anionoid dyes of the malonocyanine class have all the inherent properties of a polymethine state, i.e., alternation of charges and leveling of bonds, and these are also characteristic of cationic streptopolymethines. According to the calculation data, the introduction of bridging groupings causes considerable changes in the electronic structure of the cyanine dyes, as confirmed by the results of the study of their ¹³C NMR spectra.Translated from Teoreticheskaya i Ékperimental'naya Khimiya. Vol. 23, No. 6, pp. 687–692, November–December, 1987.     

Regularities of homo- and heteroassociation of the pinacyanol cation in aqueous solution

The ability of the cation of the cyanine dye (pinacyanol) to association in an aqueous solution was studied. The most probable structures of the pinacyanol cation, its dimer, and heteroassociates with anionic forms of several dyes were proposed on the basis of an analysis of the spectral and calculated data. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1379–1389, July, 2008.     

菁染料分子中取代基效应的交替现象

本文利用同系线性规律对菁染料的取代基效应进行了研究.提出菁染料的取代基效应与通常的取代基效应不同,在菁染料分子中取代基效应存在较大的交替现象;根据取代基团的内部结构及其所在位置的关系,推导出一套经验公式,并对菁染料的电子吸收光谱进行了定量计算.本文定量地预测了由苯并硫氮茂环、萘并琉氮茂环和苯并硒氮茂环等组成的菁染料及其衍生物(共一百多个化合物)的电子吸收光谱峰值,与实验值相比,峰值偏离在±5nm内的约占70%左右,在±5-±10nm的约占25%,大于±10nm的约占5%.     

On the nature of excited electronic states in cyanine dyes: implications for visual pigment spectra

CNDO/S CI calculations are carried out on polyenes and on cyanine dyes. In contrast to polyenes, doubly excited configurations have a strong effect on the first optically allowed excited state in cyanines. Protonated Schiff bases of retinal are closely related to cyanine dyes, with important consequences for models of visual pigment spectra and photochemistry.     

DFT and TD-DFT studies on symmetrical squaraine dyes for nanocrystalline solar cells

Abstract  

The ground-state geometries, electronic structures, and electronic absorption spectra of symmetrical squaraine dyes SQ1–SQ4 were investigated using density functional theory and time-dependent DFT at the B3LYP level. The calculated geometries indicate that strong conjugation effects occur in the dyes. The highest occupied molecular orbital energy levels were calculated to be −4.95, −5.22, −5.09, and −5.06 eV, and the lowest unoccupied molecular orbital energies were −2.72, −3.05, −2.80, and −2.80 eV for SQ1–SQ4, respectively. Taking the conduction band energy of TiO₂ into account, these data reveal the sensitized mechanism: the interfacial electron transfer between the semiconductor TiO₂ electrode and the dye sensitizers SQ1–SQ4 are electron-injection processes from excited dyes to the semiconductor conduction band. The intense calculated absorption bands are assigned to π → π* transitions, which exhibit appreciable blue-shift compared with the experimental absorption maxima due to the inherent approximations in the TD-DFT.     

Theoretical study of radiationless deactivation of a series of coumarin derivatives

The electronic structures of a series of coumarin derivatives have been calculated by the INDO/S method. A dependence of the relative position of the lowest energy excited states with different orbital types and multiplicities on the length of the C=O bond has been observed for molecules which display thermal quenching of fluorescence. L. Ya. Karpov Physical Chemistry Research Institute, 10 Vorontsov Pole Ulitsa, 103064 Moscow, Russia. Poltava Department, Ukraine Academy of the Science of Technological Cybernetics, 3 Kovalya Ulitsa, 314069 Poltava, Ukraine. Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 33, No. 2, pp. 105–110, March–April, 1997.     

Influence of the interaction of chromophores of bis-cyanine dyes on the photogeneration of charge carriers in poly-N-epoxypropylcarbazole films

An increase in photoconductivity and in the extinguishing effect of an external electric field has been observed in the photoluminescence of doped poly-N-epoxypropylcarbazole films on changing from cyanine dyes with normal chromophores to the corresponding bis-cyanines. It was concluded that an increase in photogeneration of triplet electron-hole pairs arose with such replacement of the dye and that dissociation of the pairs was responsible for the photoconductivity. Translated from Teoreticheskaya i éksperimental'naya Khimiya, Vol. 34, No. 6, pp. 371–375, November–December, 1998.     

Vibrational structure of the electronic transition to the third excited singlet state of pyridine N-oxide

The electronic absorption spectrum of pyridine N-oxide vapor in the region of the third electronic transition (43,000-46,000 cm_-1) was recorded. The frequencies and intensities of vibronic bands, including the 0–0 band at 43,896 cm_-1, were measured An assignment of the frequencies of fundamental vibrations in the third electronically excited state is suggested The matrices of rotation and shift of normal coordinates due to electronic excitation are calculated, and the vibronic spectrum of pyridine N-oxide is interpreted on the basis of these matrices. Translated fromZhurnal Struktumoi Khimii, Vol. 38, No. 2, pp. 357–362, March–April, 1997.     

Spectral properties and conformations of nonlinear ketocyanines

The electronic transitions in molecules of the ketocyanine dyes (polyenic ω,ω′-bisamino ketones) were calculated by quantum chemical methods. Satisfactory agreement was obtained between the experimental bands of the S-S absorption spectra and calculated electronic transitions for the ketocyanine with the central pyranone moiety and the corresponding salt assuming an acute angle between the chromophores and for the ketocyanine with the central pyridone moiety assuming an obtuse angle between the chromophores. Such molecular conformations were confirmed by the gNOESY ¹H NMR data for these dyes. The difference in the conformations of the dyes with the pyranone and pyridone moieties is due, most likely, to steric hindrance created by the central methyl groups in the molecules of the latter. The salts corresponding to these dyes have similar conformational differences. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1954–1958, October, 2007.     

Steric factors in the reaction of 2,6-bis(formylphenoxymethyl)pyridines with primary diamines

On the basis of the results from theoretical calculation of the molecular conformations it was suggested that the predominant factor in the construction of the macrocyclic Schiff bases of 2,6-bis(2-formylphenoxymethyl)-pyridines and 2,6-bis(4-formylphenoxymethyl)pyridines is the number of methylene units in the initial diamine. The populations of the "reactive" conformers are lowest in the case of meta-dialdehydes. A. V. Bogatskii Physical Chemistry Institute, National Academy of Sciences of Ukraine, 86 Lyustdorfskaya Doroga, Odessa 279980, Ukraine. Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 34, No. 2, pp. 91–95, March–April, 1998.     

Iridium (I) and Platinum (II) Complexes with Cyanine Dye Base Ligands

The preparation of cyanine dyes by coordination of cyanine dye bases with transition metals is described. The significance of these complexús for the realization of an excitonic high temperature superconductor is discussed.     

AB Initio calculations and vibrational spectra of CH3SC≡CH and CH3SC≡CSCH3

Methylthio- (MTE) and bis-methylthioethyne (BMTE) molecules are calculated by the SCF MO method (geometry optimization, basis set 6–31G*/MP2). The calculated internal rotation barriers of methyl groups are 7.12 kJ/lmole for MTE and 12.86 kJ/mole for BMTE (both groups are simultaneously rotated). The s-gosh-orientation of the thiomethyl fragments corresponds to a stable conformation of BMTE. The estimated values of the s-cis- and s-trans-barriers of mutual rotation of SCH₃ groups about the axis of the C≡C bond are 13.61 and 12.54 kJ/mole, respectively. Conformationally sensitive MOs and vibration frequencies are established. An analysis of the experimental IR absorption and Raman spectra and the calculated vibrational spectrum makes it possible to conclude that in the liquid phase the BMTE molecules also have an s-gosh-conformation. Translated fromZhumal Strukturnoi Khimii, Vol. 39, No. 4, pp. 602–609, July–August, 1998.     

Syntheses and absorption-structure relationships of some new photosensitizer cyanine dyes

New biheterocyclic compound was synthesized as starting material to prepare new photosensitizers mono-, tri-, substituted tri-, azadimethine and mixed cyanine dyes. Absorption-structure relationship of the synthesized cyanine dyes were determined by studying their electronic spectral behaviour in ethanol. The structure of the compounds were identified by elemental analysis, IR and¹HNMR spectral data.     

NMR studies of the electronic structure of coumarins

¹H and¹³C NMR spectra of a series of coumarin dyes used as active laser media are studied. Electron densities and ring currents are calculated. Formulas for calculating¹³C NMR chemical shifts from quantum mechanical data for aminocoumarins are suggested. NMR data and electronic structure calculations are used to explain the generation properties of coumarins. Translated fromZhurnal Strukturnoi Khimii, Vol. 38, No. 3, pp. 495–502, May–June, 1997.     

Peculiarities of the mechanism of chlorotropic and conformational isomerism in a series of chloromethyl isocyanates

The thermodynamic and kinetic stability of chlorotropic isomers in a series of chloromethyl isocyanates Cl_3−nH_nC−N=C=O, where n=0, 1, 2, has been shown by quantum chemical calculations, using the MNDO method, and by³⁵Cl NQR spectroscopy. The phase transformations of two polymorphic modifications of N-chlorocarbonyl dichloride, which is a stable iminocarbonyl form of trichloromethyl isocyanate with small conformational activation barriers, have been studied. Institute of Bioorganic and Petrochemistry, National Academy of Sciences of Ukraine, 1 Murmansk ul., Kiev-94 252660, Ukraine. Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 34, No. 3, pp. 164–169, May–June, 1998.     

Ab initio quantum chemical calculations of enolized and deprotonated forms of Β-diketones and their derivatives

The data of ab initio quantum chemical calculations of Β-diketones and their anions performed in split valence-shell bases are presented. These compounds are of great interest as ligands in numerous chelate complexes. The electronic structures of substituted enolized Β-diketones containing the period III elements S and Cl are compared. It is shown that using the Huzinaga pseudopotential for describing core electronic shells makes it possible to adequately reproduce the main peculiarities of the structure of the outer electronic layers at a qualitative level. The basis used substantial affects on the calculated values of atomic charges, bond orders, and dipole moments, whereas the one-electron energies are less sensitive to the choice of the basis. Translated fromZhurnal Struktumoi Khimii, Vol.40, No. 2, pp. 234–241, March–April, 1999.     

New Calix[4]arene Based Hydroxystyryl Cyanine Dyes

Calix[4]arene derivatives bearing one or two hydroxystyryl cyanine chromophores at the wide rim of the macrocycle have been synthesized. The influence of bases and Li⁺ on the UV–Vis spectra of the compounds obtained has been investigated.