The use of a tertiary solvent mixture to study solvent dynamic effects in the photoinduced electron transfer reaction of excited singlet pyrene and indole

In a series of tertiary solvent mixtures comprising propyl acetate (PA), butyronitrile (BN) and diethyl phthalate (DEP), spanning a wide range of dielectric constants (5.90 < ϵ_s < 23.4) while maintaining both refractive index and viscosity constant, rate constants of photoinduced electron transfer (PET) reactions between excited pyrene and indole were measured and compared with those obtained in single neat organic solvents. Quenching rate constants were studied using the Stern-Volmer method and dynamic quenching was confirmed by time-correlated fluorescence lifetime measurements. In a previous study using different pure organic solvents and varying all solvent parameters (Previtali et al.), the solvent dependence of the pyrene/indole pair was described based on the semi-classical theory of adiabatic and non-adiabatic electron transfer reactions. Here the pure rate dependence on the dielectric constant is reported.