Molecular entity that acts as the electron donor in a photoinduced electron transfer process and is not restored in a subsequent reduction process but is destroyed by irreversible chemical conversion.
Source:
PAC, 1996, 68, 2223. 'Glossary of terms used in photochemistry (IUPAC Recommendations 1996)' on page 2272 (https://doi.org/10.1351/pac199668122223)