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

The electron-transfer(ET) fluorescence quenching of aromatic compounds by a liphatic amines (DABCO, ABCO, and triethylamine) was studied in acetonitril e. The fluorescence quenching rate constant k(q) suddenly decreases when th e free energy change (DeltaG(fet)) of full ET in fluorescence quenching inc reases 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 q uencher are aromatic. The fluorescence quenching distance r(q) increases wi th decreasing DeltaG(fet) and the rate k(bet) Of back ET within geminate ra dical pairs shows a bell-shaped dependence on the free energy change (Delta G(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 Else vier Science B.V. All rights reserved.