FLUORESCENCE BEHAVIOR OF CYANOBIPHENYL LIQUID-CRYSTAL MOLECULES IN LIQUID CRYSTAL POLYMER COMPOSITE FILMS/

The fluorescence behaviour of the liquid crystal, 4-cyano-4'-pentylbip henyl (5CB), in composite thin films prepared by the photopolymerizati on of 5CB/diacrylate mixtures, was investigated by means of three diff erent excitation methods, in which the total-internal-reflection or su rface-limited excitation method was used for analysis of the fluoresce nce from an ultra-thin interface layer (< 100 nm) in contact with the substrate surface, whereas the fluorescence from the interior bulk was analysed by the through-film excitation method. It was found that int ensity ratios of the monomer and excimer emissions of 5CB are signific antly lower in the interface layer than in the interior bulk, dependin g upon photopolymerization conditions as well as upon the structures o f the diacrylates used. Scanning electron microscopic observations and light-scattering measurements of some typical composite films showed possible relationships between morphological features and fluorescence characteristics depending upon the diacrylate structures and polymeri zation conditions. The different fluorescence behaviour has been discu ssed in terms of differences in mobility and/or aggregation degrees of 5CB molecules arising from dominant molecular interactions with the s ubstrate and polymer surfaces.