FLUORESCENCE QUENCHING OF PYRENE BY WEAK ELECTRON-DONORS AND ACCEPTORS IN POLAR MEDIA - THE ROLE OF EXCIPLEXES IN THE FORMATION OF TRIPLET-STATES AND RADICAL IONS

The kinetics of formation and decay of triplet species and radical ion s, die transient products of fluorescence quenching of pyrene by weak electron donor and acceptors in polar media was studied using a techni que of microsecond flash photolysis. The observed dependences of quant um yields for triplets and radical ions on quencher concentration disa gree with the model of direct electron transfer in the excited state, but are consistent with the model of exciplex formation in a polar med ium. It was shown that the formation of triplet fluorophore occurs pre dominantly via two pathways: by intersystem crossing from a singlet ex cited state of fluorophore and from a singlet exciplex. The free radic al ions are formed from the exciplex due to its dissociation accompani ed by the complete charge transfer from the donor to the acceptor.