ACRIDINE-9-CARBOXYLATE AS AN EFFICIENT TRIPLET-STATE MEDIATOR OF PHOTOSENSITIZED ELECTRON-TRANSFER REACTIONS VIA A REDUCTIVE QUENCHING PATHWAY

The triplet (T1) state of acridine-9-carboxylate (AcrCOO-) is shown by laser flash photolysis to be an efficient mediator of electron transfer from both a water-soluble analogue of vitamin E (Trolox) and ascorbic acid to methyl violgen (MV2+) in aqueous 0.1 M NaHCO3 solution (pH 8.3) at 22-degrees-C. The reaction proceeds via a reductive quenching mechanism generating the semireduced species HAcrCOO.-, which subsequently reduces MV2+ to MV.+. HAcrCOO.- has an absorption maximum at 502 nm with an extinction coefficient of 4000 M-1 cm-1. The reduction potential of HAcrCOO.- is estimated to be close to -0.55 V versus NHE based on its bimolecular rate constant for reaction with a series of bipyridinium salts whose potentials span the range -0.36 to -0.74 V.