Mechanistic insight into circularly polarized photoluminescence from a chiral-nematic film

Abstract

Circularly polarized photoluminescence (CPPL) was characterized for rod-like molecules of Exalite 428 helically arranged in a chiral-nematic liquid crystalline film. With an unpolarized excitation at 370nm, CPPL intensities measured at 428nm, and a selective reflection wavelength ranging from 7.2 to 72.6mum, the observed dissymmetry factor, g, was found to be in excellent agreement with theoretical prediction, without resorting to adjustable parameters. As a result, new insight into liquid crystal-induced CPPL has emerged. Specifically, it was found that circular dichroism and circular polarization of the excitation beam prior to inducing linearly polarized photoluminescence (LPPL) at quasi-nematic layers play an insignificant role. The relatively large g value in the spectral region far removed from the selective reflection band was attributed to the circular polarization of LPPL emanating from all quasi-nematic layers comprising the chiral-nematic film. In the absence of a fluorescent dye, the propagation of unpolarized light through the chiral-nematic film under otherwise identical conditions results in no circular polarization. The present study has provided a foundation for generating circularly polarized light by way of photo-excitation with unpolarized light of a chiral-nematic film containing a fluorescent dye. e e