Origin of the Photoluminescence of a Banana-Shaped Liquid Crystal

Abstract

We have investigated the optical absorption and photoluminescence (PL) of a classical banana-shaped liquid crystal, 1,3-phenylene-bis[4-(4'-nonyloxy)phenyliminomethyl]benzoate, in dilute solutions of tetrahydrofuran. Upon the 325 nm excitation from a helium-cadmium laser, the dilute tetrahydrofuran solutions of the banana-shaped compound gives off strong PL with its peak located at about 380 nm (3.26 eV). Interestingly the PL spectrum of the banana-shaped compound has a long tail that extends beyond 500 nm. In order to explore the origin of the PL, we have calculated the electronic structures of the three chromophores in the banana-shaped compound: the central benzene ring (chromophore A), the carbonyl linkage (chromophore B), and the Schiff base bridged two benzene rings in the branched arms of the molecule (chromophore C). Our results have shown that chromophore C is responsible for the 380 nm PL band where the chromophore B is responsible for the long tail in the recorded PL.