Photochemistry and photophysics of some mono and bichromophoric aryl cinnamate model compounds

Rabih Omran Al-Kaysi

Abstract

Liquid crystalline polymers (LCP) containing aryl cinnamate pendant groups exhibit a wide range of photochemical and photophysical behavior which depends on the phase type and chromophore aggregation in the polymer film. The UV-spectrum of an LCP in the solid state is blue shifted, with respect to that in a good solvent. The photochemistry is also different when a film and a solution sample of the LCP are irradiated at 366 nm. Studies of several small molecule model compounds show that these spectral differences are due to the ground state aggregation of the chromophores, not to chromophore twisting. Several bichromophoric small molecule model compounds were studied in an attempt to model the spectral changes in the polymer films. Compounds such as 11 containing two aryl cinnamate chromophores were synthesized and characterized. The UV-spectra of these model compounds were collected in solution and as dilute dispersions in a polymer matrix. Compound 11 shows spectral changes attributed to aggregation but different from the effects seen in the liquid crystalline polymer. The photochemistry of 11 and 7 was also investigated and similar effects to those seen in the polymer film were observed. Irradiation at 366 run of a dilute dispersion of 11 in hydrogenated polystyrene (H-PS) showed predominant 2+2 cycloaddition when compared to model compound 7 in H-PS. Several other model compounds were synthesized and studied.* *Please refer to dissertation for diagrams.