COLUMNAR LIQUID-CRYSTALS OF TRIARYL PYRYLIUM-SALTS - EXPERIMENTAL ANDTHEORETICAL-STUDY OF PHOTOPHYSICAL PROPERTIES

Polarized absorption and fluorescence spectra of columnar liquid cryst als formed by triaryl pyrylium salts are reported. The great Stokes sh ift and the time-resolved evolution of the fluorescence observed follo wing laser excitation are interpreted by means of a theoretical model. based on the excitonic theory and quantum chemistry. The results conc erning the energetic topography (excitation energy as a function of th e position of the excited chromophore) and the simulated fluorescence spectra of columnar aggregates are reported. The influence of orientat ional defects on the photophysical properties is investigated. Accordi ng to this model, absorption corresponds to coherent excitation while fluorescence may arise either from collective excited states or from l ocalized ones related to defects.