Aromatic ring size effects on the photophysics and photochemistry of styrylbenzothiazole

The effect of ring size on the photophysics and photochemistry of styrylbenzothiazole has been investigated via systematic replacement of the phenyl ring of 1-phenyl-2-(2-benzothiazolyl)ethene with naphthyl and phenanthryl rings. Steady state absorption and fluorescence techniques have been employed to record the spectra in a variety of solvents, in conjunction with density functional theory (DFT) calculations, to probe absorption spectra and other properties of relevance to photo-excitation. Important experimental parameters were determined, such as fluorescence quantum yield and quantum yields of photochemical E-Z isomerisation. In addition, the computed potential energy surfaces of the ground and excited states were constructed using DFT/TD-DFT methods that showed that the photo-reaction is based on an adiabatic mechanism, in the sense that the reaction occurs via the excited-state potential energy surface. Based on the significant blue shift of the Z-isomer absorption maximum relative to that of the E-isomer, and the high percentage of Z-isomers in the photo-stationary state, these compounds may serve as potential promising candidates for optical data storage applications.