Photoinduced Electron-transfer Employing Organic-anions

Reductive properties of excited state organic anions are discussed, starting from the preliminary presentation of other related properties: spectral characteristics, ion pair associations and photoejection ability. Electron transfer reactions may be correlated by the Marcus treatment and some peculiarities of the use of this model, in the case of oxyanions, are pinpointed. Photoreactions employing an electron transfer are discussed. Among these are recent examples of photochemical S(RN)1 reactions, photoalkylations of carbanions and photoreductions initiated by oxyanions and radical anions. Anions used in their ground state as electron donating quenchers are also considered. Intra ion pair electron transfers as well as the use of anion-like precursors in charge transfer complexes or charge transfer excited states are presented

Photosensitizers Covalently Anchored To the Silica Surface - Modulation of the Excited-state Efficiency Through Electron-transfer From the Linking Arm Or From the Surface

Benzophenone derivatives have been anchored on silica in different ways. The so obtained heterogeneous as well as the corresponding homogeneous triplet photosensitizers have been tested in the triplet state isomerization of trans to cis stilbene. A photoinduced electron transfer originating from the amino groups on the linking arm or on the silica surface is found to modulate the sensitizer efficiency

Photosensitizers covalently anchored to the silica surface: Enhanced efficiency of heterogeneous photodechlorination of chlorinated aromatics.

A naphthol sensitizer is covalently anchored on silica. The so obtained heterogeneous as well as the corresponding homogeneous photosensitizer, under anionic form, have been tested in the reductive dechlorination of chloroaromatics. In these photoinduced electron transfer (PET) sensitized reactions, interactions between the sensitizer and the surface are shown to enhance their reactivity. The grafted silica is shown to work in the dechlorination of a tetrachlorobiphenyl acid sunlight reactions have been performed

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

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

Electron-transfer Photochemistry Initiated From a Twisted Intramolecular Charge-transfer State Used As An Electron-donor and As An Acceptor

Electron transfer photochemistry starting from a twisted intramolecular charge transfer (TICT) excited state is shown, using N-(alpha-naphthyl)carbazole (NC) as sensitizer. The NC TICT state has been used as electron donor and acceptor. This dual reactivity is demonstrated by fluorescence quenching measurements, and the rate constants have been correlated with the help of the Marcus equation. Photochemical reactions have also been performed. Photoisomerization of the quadricyclane into norbornadiene is proof of the radical cationic reactivity of the TICT, while photodechlorination of pentachlorobenzene is proof of radical anionic reactivity. A triplet sensitized ring closure of norbornadiene was also shown to occur