Photoinduced charge separation in rigid bichromophoric compounds and CT state electron transfer reactivity

(eng) Bichromophoric compounds giving, after photoexcitation, a locally excited state (LE) rapidly followed by an intramolecular charge transfer (CT) state were designed using a Paddon-Row type synthesis. The electron-accepting end of the CT state is chosen in order to play the role of an electron relay versus external accepters. In this way, electron transfer photosensitization is made available by using the CT state of bichromophores. The photophysics of the synthesized bichromophores is discussed; and the reductive dechlorination of polychlorinated benzenes is used as a test reaction. The bichromophoric sensitizer is unexpectedly found to be totally regenerated: the reaction is shown to be initiated by an electron transfer from the CT state to the chlorinated quencher. A rapidly breaking radical anion leads to the dechlorination, while the recombination of the sensitizer radical cation with the released chloride anion opens the way to the sensitizer recovery.