Circularly polarized fluorescence from chiral nematic liquid crystalline films: theory and experiment

A theory was formulated for the description of circularly polarized fluorescence (CPF) from a chiral nematic film in the spectral region outside the selective reflection band. The CPF theory incorporates: (1) the ability of a chiral nematic film to accomplish both circular dichroism and circular polarization and (2) linearly polarized fluorescence from chromophores unaxially aligned in the nematic sublayers comprising 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 experimentally determined dissymmetry factor using both left- and right-handed circularly polarized excitations was found to be in good agreement with the theoretical prediction with all the system parameters determined a priori. The theory was also employed to furnish insight into the effects of the concentration of the fluorescent dye and chiral nematic film thickness on the dissymmetry factor.