Quantum chemical calculations and experiments on model compounds are used to study the effect of conformational changes on intramolecular electron transfer in perylenebisimide-biphenyl dyads. The molecular orbital energy level of the biphenyl moiety and thus the free energy change for electron transfer depends on the dihedral angle between the two phenyl rings. Dramatic changes in the orbital energy levels result in very different electron transfer behavior for three model compounds. These changes are accurately predicted by calculations using density functional theory, which also give accurate results for geometries, suggesting such calculations can be useful in designing molecular electronic species. (c) 2005 Published by Elsevier B.V.