The dynamics for back electron transfer within the trans-stilbene/fumaronitrile contact radical ion pair have been analyzed within a theoretical model for electron transfer developed by Jortner and Bixon (J. Chem. Phys. 1988, 88, 167) in order to derive the solvent dependence of the electronic coupling matrix element for a series of nitrile solvents. The solvent reorganization energy is calculated from a dielectric ellipsoidal cavity model. The electronic coupling increases from 620 +/- 60 cm-1 in acetonitrile to 750 +/- 60 cm-1 for pentanenitrile.