Rate constants kg of the fluorescence quenching of 9,10-dicyanoanthracene b
y bromide and chloride ions and of 9-cyanoanthracene by bromide ions were d
etermined in the low polar solvent dichloromethane with a series of tetra-a
lkylammonium counterions. Cation size dependent electron transfer rate cons
tants k(et) were derived from k(q), and were fitted to a nonadiabatic elect
ron transfer model equation. Because of ion pair formation in dichlorometha
ne electrostatic interactions of the redoxinert countercations during elect
ron transfer were considered. Accordingly, the position of the countercatio
n within the precursor complex had to be described.
The electronic coupling matrix element derived by fitting of the experiment
al data is in satisfactory agreement with results of simple quantum chemica
l calculations. (C) 2000 Elsevier Science S.A. All rights reserved.