INFLUENCE OF EXCIPLET FORMATION IN POLAR MEDIA ON FLUORESCENCE QUENCHING MECHANISMS

The fluorescence quenching of pyrene by a number of electron donors an d acceptors has been studied in polar solvents. It was found that the experimental quenching activation energy in the kinetic regime where t he Gibb's free energy for electron transfer is nearly zero or positive , is substantially lower than energies corresponding to experimentally measured rate constants within the context of the classical model of complete electron transfer. In some instances, the energies were of op posite sign. A model is proposed which includes a stage involving form ation of a weakly polar exciplet, even in polar solvents. The model de scribes well data obtained in this study and present in the literature .