Photochemistry of Polyfunctional Molecules. Development of Antenna Chromophores for Self‐sensitized Photoreduction of Ketones*

Abstract –Model systems are reported which test the efficacy of potential aryl antenna groups designed to harvest photons and subsequently transfer electronic energy to a target ketone through singlet‐singlet energy transfer. The model series consists of 4‐aryl substituted cyclohexanones where the aryl groups are benzyloxy (5a), benzoyl (5b), and dimethylphenylsiloxy (5c). In each case, photolysis of isopropyl alcohol solutions of the substrate with 254 nm light results in photoreduction of the ketone to the corresponding alcohols, 6a‐6c. The most efficacious sensitizing antennae are the benzyloxy and dimethylphenylsiloxy chromophores, with quantum efficiencies for reduction equal to 0.57 and 0.48, respectively. Photophysical and photochemical studies on 5a confirm that energy transfer to the ketone is intramolecular with the rate constant for energy transfer estimated at 2.4 × 100 s‐1.