A comparative study on electron-transfer fluorescence quenching by aliphatic and aromatic amines

The electron-transfer(ET) fluorescence quenching of aromatic compounds by aliphatic amines (DABCO, ABCO, and triethylamine) was studied in acetonitrile. The fluorescence quenching rate constant k(q) suddenly decreases when the free energy change (DeltaG(fet)) of full ET in fluorescence quenching increases from -0.6 to -0.4 eV, indicating that the downhill region shifts by ca. -0.5 eV compared with the Rehm-Weller plot, where both fluorescer and quencher are aromatic. The fluorescence quenching distance r(q) increases with decreasing DeltaG(fet) and the rate k(bet) Of back ET within geminate radical pairs shows a bell-shaped dependence on the free energy change (DeltaG(bet)) Of back ET. Both free energy dependence of r(q) and k(bet) are the same as those of aromatic electron donor and acceptor system. (C) 2000 Elsevier Science B.V. All rights reserved.