Raman and Fluorescence Studies of Thermotropic Liquid-Crystalline Oligomers with Different Type of Coils

摘要

Raman and fluorescence spectroscopies were employed to study the coil effects on the intermolecular structure of a rod-coil liquid crystalline (LC) oligomer,the esterification products of ethyl 4-[4'-oxy-4-biphenyl-carbonyloxy]-4'-biphenylcarboxylate with poly(propylene)oxides (PPO) (DP=12) and poly(ethylene oxide)s (PEO) (DP=12).Three different vibrational modes (carbonyl,aromatic C-H,and aromatic C=C) obtained from the Raman experiment at variable temperature indicate that PPO and PEO coils induce the hydrogen bonding in a different manner.Further information about the micro-environment around the mesogenic unit obtained by fluorescence excitation spectra of P12-4 (LC with PPO coil) and 12-4 (LC with PEO coil) suggests that the mesogenic unit of P12-4 is quite different from that of 12-4 in intermolecular structure.This study supports the results obtained only from Raman spectroscopy,providing more accurate information about the intermolecular structural changes of liquid crystalline polymers at a molecular level during the phase transitions.