An antenna triplet sensitiser for 1-acyl-7-nitroindolines improves the efficiency of carboxylic acid photorelease.

Conjugates of a triplet sensitiser (a 4,4'-dialkoxybenzophenone) with 1-acetyl-7-nitroindolines show up to 20-fold enhancement for photorelease of acetate (relative to the same indolines lacking the attached sensitiser) upon irradiation at 300 nm in neutral aqueous solution. The sensitised photolysis can be carried out in the presence of dissolved oxygen and will be applicable to photorelease of other carboxylates. The enhanced efficiency is mediated by an antenna function of the sensitiser, which transfers its triplet energy to populate the reactive, short-lived triplet state of the acylnitroindoline. This energy transfer is confirmed by a large reduction of the sensitiser's triplet lifetime in the conjugates compared with that of the sensitiser alone.