Eugenia V. Vovk

Spectroscopic investigation of molecular association in thin films of mesogenic cyanophenyl derivatives

Abstract Molecular association of liquid-crystalline 4,4−pentylcyanobiphenyl (5CB), 1-p-cyanophenyl-4-pentyl-cyclohexane (5CH) 2-p-cyano-phenyl-5-pentylpyridine (5Py) was studied in thin films, solutions and inert matrices at 77–330 K by low-temperature reflection IR spectroscopy. The thermodynamic parameters have been obtained for cyanophenyl molecule dimerization in the nematic mesophase. The factors affecting the dimer stability were considered.

Thermal behavior of silver-containing mesogenic cyanobiphenyl films

Abstract Formation of nanostructures in metal-mesogenic co-condensate films have been studied during low temperature codeposition of metal and organic component vapors—long chain alkyl(alkoxy)cyanobiphenyls (CB): C n H 2 n +1 →C n H 2 n +1, where n =5 (5CB), 8 (8CB), and C n H 2 n +1 OC 6 H 5 C 6 H 5 CN, n =8 (8OCB). The existence of low temperature Ag–CB complexes was shown by IR, UV-visible and ESR techniques. Thermal degradation of the complexes by annealing of the samples up to 300 K led to the formation of nanosize (15–30 nm) silver particles incorporated in anisotropic CB-structure and their further aggregation in mesogenic matrices.

Synthesis and properties of metal-mesogenic nanostructures

Abstract Formation of metal–organic nanostructures in co-condensate films have been studied during low temperature codeposition of metal and organic component vapours using a new class of mesogenic ligands-long chain alkyl(alkoxy)cyanobiphenyls (CB): C n H 2 n +1 –C 6 H 5 –C 6 H 5 –CN, where n =5 (5 CB), 8 (8 CB), and C n H 2 n +1 O–C 6 H 5 –C 6 H 5 –CN, n =8 (8 OCB). The existence of low temperature Ag-5CB complexes was shown by IR–UV–Visible and ESR techniques. By performing ab initio quantum chemistry calculations including partial geometry optimization and vibrational analysis for the sandwich-like cyanobenzene–silver complexes, it is shown that the observed red shifts in the CN stretching region of the IR spectra of silver–cyanobiphenyl condensate films is a consequence of the formation of the π-complexes. Thermal degradation of the complexes by annealing of the samples at 200–300 K led to the formation of nanosize (15–30 nm) silver particles incorporated in anisotropic CB-structure and their further aggregation in mesogenic matrices.

Production and spectroscopic study of low-temperature silver complexes with mesogenic cyanobiphenyl derivatives

Abstract Metal-containing liquid-crystalline systems were obtained by co-condensation of metallic silver vapour with evaporated liquid-crystalline 4-pentyl-4′-cyanobiphenyl (5CB) under conditions of molecular beams. A comprehensive infra-red and ultraviolet-visible spectroscopic study of Ag-5CB film samples of different component ratios at 80 K shows the existence of Ag-5CB complexes owing to interactions of Ag with the π-electrons of the CN bond of cyanobiphenyl molecules.

Spectroscopic Study of Silver-Containing Mesogenic Cyanobiphenyls in Solid Phase

Abstract Silver-containing mesogenic alkylcyanobiphenils (CB): CnH2n+1-C6H5-C6H5-CN, where n=5 (5 CB), 7 (7 CB), and 8 (8 CB) systems were obtained by low temperature co-condensation of metal and organic component vapours. The formation of low temperature Ag-CB complexes was shown by IR-, UV-visible and ESR techniques. Thermal degradation of the complexes led to the formation of nanosize (15–30) silver particles and their further aggregation in anisotropic matrices.

IR spectroscopic study of molecular aggregation in condensate films of polar liquid crystals

Abstract Molecular association in polar liquid crystals influences almost all physical and chemical properties of these compounds and is of great importance for their use as materials for molecular electronics. There are only few reports available that present estimations of the degree of dimerization and enthalpy via dielectric measurements of bulk samples and of solutions in non-polar solvents. In the present work, the molecular aggregation of liquid-crystalline 4-pentyl-4′-cyanobiphenyl (5CB), 4-pentyl-4′-cyanophenyl pyridine (5Py), 4-pentyl-4′-cyanophenylcyclohexane (5CH), 4-octyl-4′cyanobiphenyl (8CB) and 4-octyloxy-4′-cyanobiphenyl (8OCB) in molecular condensate films and inert matrices has been studied by low-temperature reflection and transmission vibrational spectroscopy in a wide temperature range from 80 to 330 K. A red shift of the CN stretching vibration band was considered to be due to the formation of molecular aggregates. The factors affecting their thermodynamic stability are considered.

IR SPECTROSCOPIC STUDY OF MOLECULAR ASSOCIATES OF MESOGENIC CYANOPHENYLS

Molecular association greathy affects the physicochemical properties of mesogenic cyanophenyls, which are currently widely used as molecular materials for optoelectronics. This paper reports on a polythermal IR spectroscopic study of molecular association for mesogenic alkyl/alkoxycyanobiphenyls and their hydrated and heteroaromatic analogs in nonpolar solutions, low-temperature inert matrices, and molecular condensate layers in the temperature ranges of 5–10 and 80–330 K. Correlation of the thermodynamic parameters of association with molecular structure of cyanophenyls is established.

THE ELECTRONIC ABSORPTION SPECTRA AND MOLECULAR AGGREGATE FORMATION IN VACUUM DEPOSITED FILMS OF MESOGENIC CYANOBIPHENYLS AND THEIR SOLUTIONS

Abstract Electronic absorption spectra of mesogenic 4-pentyl-4′-cyanobiphenyl (5CB), 4-octyl -4′-cyanobiphenyl (8CB) and 4-octyloxy-4′-cyanobiphenyl (8OCB) films produced by cyanobiphenyl molecular vapor deposition were measured. The appearance of the spectral changes during annealing and dissolution of cyanobiphenyl film samples are discussed assuming molecular dimerization and H-aggregate formation.

Spectroscopic Study of Some Mesogenic Cyanophenyls in Condensate Films and Inert Matrices

Abstract In present work the molecular aggregation and interaction with metallic silver of liquid crystalline 4-pentyl-4′-cyanobiphenyl (5CB),4-pentyl-4′-cyanophenyl pyridine (5Py). 4-pentyl-4′-cyanophenylcyclohexane (5CH), 4-octyl-4′-cyanobiphenyl (8CB), 4-octy-loxy-4′-cyanobiphenyl (8OCB) in molecular condensate films and inert matrices has been studied by low temperature reflection and transmission vibrational spectroscopy in a wide temperature range 80–330 K. The red shift of CN-stretching vibrations band was found to be due to molecular aggregates formation. The factors effecting on their thermodynamic stability are considered.

Low Temperature Reactions of Mesogenic Cyanophenyls in Solid Phase and Inert Matrices

Abstract In present work the molecular aggregation and interaction with metallic silver of liquid crystalline 4—pentyl—4′—cyanobiphenyl (5CB), 4—pentyl—4′—cyanophenyl pyridine (5Py), 4—pentyl—4′—cyanophenylcyclohexane (5CH), 4—octyl—4′—cyanobiphenyl (8CB), 4–8OCB) in molecular condensate films and inert matrices has been studied by low temperature reflection and transmission vibrational spectros—copy in a wide temperature range 80–330 K. The red shift of CN—stretching vibrations band was found to be due to molecular aggregates and low temperature Ag—5CB complexes formation. The factors effecting on their thermodynamic stability are con—sidered. Comprehensive IR—and UV—Vis—study of Ag—5CB film samples of different component ratio at 80K shows the exis—tence of Ag—5CB complexes due to Ag interactions with π—electrons of CN—bond of cyanobiphenyl molecules.