EXCIMER FORMATION IN MAIN-CHAIN POLYMER LIQUID-CRYSTALS WITH MESOGENIC PARA-PHENYLENEDIACRYLIC ACIDS

Polyesters of p-phenylenediacrylic acid (PDA) and various ethylene glycol derivatives (di-, tri-, tetra-, and penta-) have been found to exhibit liquid-crystalline (LC) behavior. Annealing of the polymer liquid crystals (PLC) at LC temperatures was essential for PLC to form a LC phase, and the ethylene glycol spacers strongly affected growth of the LC phase. Structure of the LC phase seemed to be different among the PLCs as evidenced by the thermodynamic data of the PLCs. Excimer formation behavior of PLCs was investigated by both steady-state and time-resolved measurements of fluorescence with the aid of a picosecond single-photon-counting system. Excimer was found to be formed much more effectively in the LC state than in the isotropic state of PLCs, due to parallel orientation of the chromophores in the LC state. Time-resolved measurements revealed that excimer formation resulted mainly from excitation of preformed chromophore pairs in the ground state. Lifetimes of excimer were found to be longer in a more ordered system due to restricted mobility of the PDA chromophores in such a system. © 1990, American Chemical Society. All rights reserved.