CIRCULARLY-POLARIZED FLUORESCENCE FROM CHIRAL NEMATIC LIQUID-CRYSTALLINE FILMS - THEORY AND EXPERIMENT

A theory was formulated for the description of circularly polarized fl uorescence (CPF) from a chiral nematic film in the spectral region out side the selective reflection band. The CPF theory incorporates: (1) t he ability of a chiral nematic film to accomplish both circular dichro ism and circular polarization and (2) linearly polarized fluorescence from chromophores unaxially aligned in the nematic sublayers comprisin g the film. Chiral nematic fluid films consisting of a nematic fluid, BDH 18523, and a chiral dopant, cholesteryl oleate, were prepared for hosting 1,6-diphenylhexatriene as a fluorescent dye. The experimentall y determined dissymmetry factor using both left- and right-handed circ ularly polarized excitations was found to be in good agreement with th e theoretical prediction with all the system parameters determined a p riori. The theory was also employed to furnish insight into the effect s of the concentration of the fluorescent dye and chiral nematic film thickness on the dissymmetry factor.