This thesis deals with two aspects of the chemistry of pyrazolotriazole azomethine dyes (PT dyes): a), the kinetics and yield of photoinduced isomerisation and b). the kinetics of dye hydrolysis in acidic and basic media. Microsecond flash photolysis has been used to investigate the effects of solvent, excitation wavelength and oxygen on the yields of photoinduced isomerisation for a range of pyrazolotriazole azomethine dyes substituted at the 6-position. The rates of thermal relaxation show no obvious dependence on solvent solvatochromic parameters examined; this suggests that solvent factors such as dielectric properties and basicity are not uniquely significant in determining the relaxation times of the dye isomers. The isomer yields for the two dyes examined with substituents which contained the carbonyl group, i.e. 6CO2Et-PT and 2COPh-PT show an unexpected dependency on excitation wavelength and on the presence or absence of oxygen. It is tentatively suggested that this is a consequence of the availability of substituent localised carbonyl excited states for these dyes. It is suggested that these states are populated by uv excitation to give a localised carbonyl triplet state which can undergo energy transfer into the pyrazolotriazole azomethine triplet state leading to relatively efficient isomerisation via the triplet manifold. There was no change observed in isomer yield when using ethyl-iodide in a nitrogen saturated solution with either 6CO2Et-PT or 6COPh-PT dyes indicating no effective external heavy atom effect from this solvent. In acid media, the pyrazolotriazole azomethine dyes undergo hydrolysis with first order kinetics. Arrhenius constants and pre-exponential constants were measured for a number of different dyes. Base hydrolyses of the 6CO2Et-PT and 6COPh-PT dyes showed second order kinetics. Preliminary investigations of acid catalysed decomposition using millisecond stopped flow suggest a complex reaction scheme involving, possibly, three successive reactions
