DERIVING INTRINSIC ELECTRON-TRANSFER RATES FROM NONLINEAR STERN-VOLMER DEPENDENCIES FOR FLUORESCENCE QUENCHING OF AROMATIC-MOLECULES BY INORGANIC ANIONS IN ACETONITRILE

The fluorescence quenching of aromatic molecules by inorganic anions in acetonitrile was investigated by stationary fluorescence measurements. The dependence of the quenching rate constants, k(q), on the free energy of electron transfer, DELTAG(et)0, obeys the well known Rehm-Weller expression which indicates that electron transfer is responsible for fluorescence quenching. Nonlinear Stern-Volmer behaviour was observed in many cases especially at very negative DELTAG(et)0 (< -0.7 eV). Distance-averaged electron-transfer transfer rate constants, [k(et)], were determined from the concentration dependence of the fluorescence quenching rates using a procedure developed by Keizer. In three cases these values can be compared with those obtained by analysis of the transient effect seen directly in picosecond time-resolved fluorescence decay curves.