Kinetic spectroscopy of pyrazolotriazole azomethine dyes

Abstract

The photophysical properties of pyrazolotriazole azomethine dyes have been investigated using both picosecond and nanosecond flash photolysis. On nanosecond timescales, prompt formation of a photoisomer is observed, the rate of decay of which shows a solvent dependence. In the presence of a triplet sensitiser a triplet pathway to the photoisomer has been established, the yield of isomer from the triplet state being considerably higher than from direct excitation. On picosecond timescales, two transients are observed; the first has a very short, solvent-independent lifetime, while the second has a longer solvent-dependent lifetime. These two transients are assigned as states formed during the relaxation of the molecules along the first excited singlet and the ground-state potential-energy surfaces, respectively. Similar kinetic behaviour is observed in a high concentration, high viscosity environment designed to mimic the photographic emulsion, indicating that the photophysical relaxation pathways are still very rapid even in this type of environment.