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

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.