Electron donor–acceptor interactions in the quenching of aromatic hydrocarbon fluorescence. The effects of temperature and solvent permittivity

Abstract

Studies of the quenching of aromatic hydrocarbon fluorescence by aromatic nitriles and 1,2,4-trimethoxybenzene in various solvents are presented and discussed with reference to the earlier experimental work of Rehm and Weller. The kinetic behaviour observed in the quenching by aromatic nitriles is not consistent with that observed in previous work. The quenching rate constants and activation parameters for ethanol solution appear to be independent of the free-energy change for electron transfer until strong exciplex interactions become possible, at which point the mechanism rapidly changes to one of diffusion-controlled exciplex formation and decay. 1,2,4-trimethoxybenzene quenches pyrene fluorescence with a rate constant which is consistent with Rehm and Weller's correlation with ΔG^⊖, but the reaction has Arrhenius parameters indicative of excited-complex formation, rather than direct electron transfer.