Synthesis,structure and complexation of biscrown-containing 1,4-distyrylbenzenes

An improved method for the synthesis of two symmetric biscrown-containing and one model tetramethoxy-substituted 1,4-distyrylbenzenes was suggested. The structures of compounds were established by ¹H and ¹³C NMR spectroscopy and X-ray diffraction analysis. Spectrophotometric and fluorescent titration were used to determine spectral properties, stoichiometry, and stability of complexes of biscrown-containing 1,4-distyrylbenzenes with alkali and alkaline-earth metal cations. The stability of the complexes was found to depend on the metal cation size and charge, as well as on the size of the crown ether fragment. The electrochemical oxidation and reduction potentials of the biscrown-containing 1,4-distyrylbenzenes and the model compound in solution were determined and their basic differences from the corresponding characteristics of biscrown-containing stilbenes were identified.     

Design of crystal packings of styryl heterocycles and regularities of [2+2] photocycloaddition in their single crystals 8. Topochemical [2+2] autophotocycloaddition and back reaction in styryl dye of the benzothiazole series

New styryl dye of the 2-benzothiazole series was synthesized. The new dye contains two methoxy groups in the benzene ring and tosylate counterion. The [2+2] photocycloaddition (PCA) of the dye was studied in the polycrystalline film and in single crystal. Two modifications of the dye cocrystallizate with hydroquinone differed in the ratio of components were obtained, and their ability to enter PCA was studied. According to the X-ray diffraction data, molecular cations of the dye form stack packings either of syn-“head-to-tail” type or relatively isolated stacking dimers. In all cases, the ethylene bonds of the adjacent cations are brought together and antiparallel, favoring PCA to form the centrosymmetric rctt-isomer of 1,2,3,4-tetrasubstituted cyclobutane. In two cases, the PCA reaction proceeded as the “single crystal-to-single crystal” transformation. Hydrogen bonds in crystals including hydroquinone molecules strengthen the crystal packing retarding the PCA. The back photoreaction (retro-PCA) was detected: it occurs without single crystal decomposition and results in the accumulation of the initial styryl dye in crystal consisting of the cyclobutane derivative. This is the first example of such a transformation in single crystals.     

Subdirect products and formations of finite groups

Translated from Algebra i Logika, Vol. 29, No. 5, pp. 523–548, September–October, 1990.     

Structural investigation of model compounds for an acceptor component of a new type of charge-transfer complexes based on viologen analogues. Characteristic features of the molecular and supramolecular structures

The crystal and molecular structures of six perchlorates (viologen analogues) are studied. These compounds serve as models of the acceptor component of new charge-transfer complexes containing bis(18-crown-6)stilbene as the donor. The polycyclic aromatic system of divalent cations is demonstrated to be virtually planar. In all cations, the side chains at the nitrogen atoms are oriented in opposite directions almost perpendicular to the plane of the cyclic system. This orientation of the spacers of these carbocations is indicative of their preorganization for the formation of 1: 2 charge-transfer complexes. Analysis of the crystal packings provides evidence that two positive charges on the conjugated systems of the organic cations and the perchlorate anions play a destructive role in the formation of stacking motifs. An increase in the size of the conjugated system and the involvement of an aromatic solvent molecule as an additional building block in a supramolecular system are favorable for the formation of a stacking supramolecular architecture.     

Crown ether styryl dyes

Novel crown-containing styryl dyes (CSD) based on 15-crown-5-substituted benzothiazole with various electron-donating groups in thepara-position of the benzene ring were synthesized. Spectral and photochemical properties ofcis- andtrans-isomers of CSD and their complexes with Mg²⁺ ions in solutions were studied. By analysis of spectral parameters and the magnitudes and directions of the shifts of absorption (fluorescence) maxima, the effects of substituents and complex formation on the photochromism of CSD were elucidated. Using quantum-chemical calculations, the possibility of controlling the degree of participation of either of the two chromophores in the long-wave electron transition by complex formation was analyzed. For Part 19, see Ref. 1. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 999–1006, May, 1997.     

Unusual supramolecular donor—acceptor complexes of bis(crown)stilbenes and bis(crown)azobenzene with viologen analogs

The results of the comprehensive study of novel supramolecular donor-acceptor complexes of bis(crown)stilbenes and bis(crown)azobenzene with viologen analogs are generalized. The original methodology for self-assembling of the organic donor-acceptor complexes possessing a very high thermodynamic stability is described. The hydrogen bonds between the peripheral fragments of the donor and acceptor play the key role in the self-assembling. The influence of different structural factors on the thermodynamic stability of the supramolecular donor-acceptor complexes and the efficiency of charge-transfer interactions between the donor and acceptor are discussed. The driving forces of the reaction leading to exotic trimolecular charge-transfer complexes are considered. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 779–787, April, 2008.     

Spectra of secondary emission during generation of optical harmonics in globular photonic crystals

Secondary emission spectra of globular silica photonic crystals when their surfaces were exposed to laser pulses 250 fs long at a power density to 1 TW/cm² have been studied. Optical harmonics and plasma emission were detected in this case. For the opal matrix containing pores filled with air, in the reflection mode, the third optical harmonic with a conversion efficiency of ～10% arises. The highest conversion efficiency for exciting radiation with wavelengths of 1026 or 513 nm is implemented when the frequencies of the exciting radiation or the second harmonic are near the stop band edge. In globular photonic crystals filled with sodium nitrite or barium titanate ferroelectrics, the second optical harmonic is observed. The exciting radiation conversion efficiency to the second optical harmonic was a few percent and depended on the frequency of exciting radiation and photonic crystal globule diameters. It is found that the plasma emission intensity increases with the exciting radiation power density. The dependences of the intensity of the second and third optical harmonics on the pump intensity are constructed for various photonic crystal globule diameters.     

Synthesis,structure, electrochemistry,and photophysics of 2,5-dibenzylidenecyclopentanones containing in benzene rings substituents different in polarity

A series of cross-conjugated dienones was synthesized to study the dependence of physicochemical characteristics on the nature of substituents in the aromatic groups of symmetric cyclopentanone dibenzylidene derivatives. The structure of compounds was established by electronic, IR, and NMR spectroscopy and X-ray diffraction study. All the compounds obtained possess the E,E-geometry. In the crystalline state, the arrangement of the dienone molecules is unfavorable for the intermolecular [2+2] photocycloaddition to take place. The low-temperature phases transition for unsubstituted diphenyl derivative of cyclopentanone was detected using variable-temperature X-ray diffraction and differential scanning calorimetry. Oxidation and reduction potentials of the dienones were measured by cyclic voltammetry. Their dependence on the nature and placement of substituents in the benzene rings was demonstrated. A linear correlation (R = 0.9343) between the difference of electrochemical oxidation and reduction potentials and the energy of the long-wavelength absorption maximum was found, that allows us to recommend the use of the data obtained in the correlation analysis of other compounds of this class.     

Photonics of 18-crown-6-containing styryl dye and its complexes with metal cations

Using absorption, luminescence, ¹H NMR, and laser kinetic spectroscopies, the photophysical processes and photochemical reactions of 4-[(E)-2-(2,3,5,6,8,9,11,12,14,15-decahydro-1,4,7,10,13,16-benzohexaoxacyclooctadecin-18-yl)vinyl]-1-ethylpyridinium perchlorate and its complexes with lithium, sodium, potassium, calcium, barium, silver, and lead perchlorates in MeCN have been studied. The styryl dye and its complexes with metal cations are capable of emitting normal (prompt) and delayed fluorescence and enter into the trans–cis photoisomerization reaction. The dye molecules in the triplet state participate in the processes of degradation of electronic excitation energy. Triplet–triplet absorption is observed only in the presence of lead cations with a maximum at 470 nm and the deactivation rate constant of the triplet state k = 2.5 × 10⁴ s^–1 in a deoxygenated solution.