Fluorescence lifetime study of intermolecular coupling between biphenyl-ester moieties of a thermotropic liquid crystal

Abstract

Using steady-state and time-resolved fluorescence spectroscopy, we investigated the intermolecular coupling between mesogenic biphenyl-ester moieties of a thermotropic liquid crystal under phase transition. In the crystalline-to-smectic C transition, a broad excitation band centered at 280 nm and a fluorescence redshift by 25 nm, followed by a drastic change in the fluorescence time-decay constant (from similar to 90 to similar to 230 ps), are consistently observed. These changes result from the intermolecular configurational change from biphenyl-biphenyl to biphenyl-ester. Emissions from intermolecular complexes such as J-aggregated biphenyls in crystalline and biphenyl-ester exciplexes in smectic C, smectic A, and isotropic phases are characterized. Crown Copyright (C) 2013 Published by Elsevier B.V. All rights reserved.