The effect of transient quenching on the excimer kinetics of 2,5-diphenyloxazole

Excimer formation in 2,5-diphenyloxazole (PPO) in ethanol is shown not to obey the expected biexponential kinetics because of the presence of time-dependent quenching. Between 25 and 50°C the decay of monomer fluorescence can be described by a model based on the linear superposition of excimer reverse dissociation and transient quenching to give values for the diffusion coefficient and the interaction radius. However, at lower temperatures the model provides an incomplete description and the indications are that this is caused by the emergence of a heterogeneous distribution of PPO molecules.