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 i n acetonitrile was investigated by stationary fluorescence measurement s. The dependence of the quenching rate constants, k(q), on the free e nergy of electron transfer, DELTAG(et)0, obeys the well known Rehm-Wel ler expression which indicates that electron transfer is responsible f or fluorescence quenching. Nonlinear Stern-Volmer behaviour was observ ed 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 tr ansient effect seen directly in picosecond time-resolved fluorescence decay curves.