A process in which, under the influence of a suitable driving force (e.g. provided by photoexcitation), electronic charge moves in a direction that increases the difference in local charges between donor and acceptor sites. electron transfer between neutral species is one of the most important examples.
Source:
PAC, 1996, 68, 2223. 'Glossary of terms used in photochemistry (IUPAC Recommendations 1996)' on page 2231 (https://doi.org/10.1351/pac199668122223)