Dynamics of Electron Transfer and Energy Transfer by New Chiral Photosensitizers

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(1)Chiral photosensitizers, Δ-[Ru(menbpy)ィイD23ィエD2]ィイD12+ィエD1 (menbpy=4,4'-bis(1R,2S,5R)-(-)menthoxycarbonyl}-2,2'-bipyridine), Δ-[Ru(phenebpy)ィイD23ィエD2]ィイD12+ィエD1 (phenebpy=4,4'-bis(1-phenethylaminocarbonyl)-2,2'-bipyridine), [Cu(tmdcbpy)(PRィイD23ィエD2)ィイD22ィエD2]ィイD12+ィエD1(tmdcbpy=4,4'-6,6'-tetramethyl-5,5'-bis(S)-(-)-1-phenylcarbamoyl-2,2'-bipyridine) were newly synthesized here. (2) Pulse radiolysis of Δ-[Ru(menbpy)ィイD23ィエD2]ィイD12+ィエD1 in ethanol yields one-electron reduced species in which ruthenium(I) is not involved but anion radical of menbpy ligand is involved. Reduction of [Co(acac)ィイD23ィエD2] by this Δ-[Ru(menbpy)ィイD23ィエD2]ィイD1+ィエD1 occurs stereoselectively with selectivity of 2.7. (3) [Cu(tmdcbpy)(PPhィイD23ィエD2)]ィイD1+ィエD1 perfomrs stereoselective photoreduction of [Co(edta)]ィイD1-ィエD1 with significantly large enantiomer excess (60% at 10% conversion), under near-UV light irradiation, while [Ru(menbpy)ィイD23ィエD2]ィイD12+ィエD1 cannot perform stereoselective photoreduction of [Co(edta)] … More ィイD1-ィエD1. (4) Photoreductions of cationic methylviologen and anionic 4,4'-bis(3-carboxyethyl)-1,1'-bipyridinium (dcbpy) by [Ru(bpy)ィイD23ィエD2]ィイD12+ィエD1 were investigated with laser flash photolysis. The reaction rate significantly depend on the electrostatic interaction; both photoinduced electron transfer from ィイD1*ィエD1[Ru(bpy)ィイD23ィエD2]ィイD12+ィエD1 to MVィイD12+ィエD1 and the reverse electron transfer from MVィイD1+ィエD1 to [Ru(bpy)ィイD23ィエD2]ィイD13+ィエD1 occur more slowly than those of dcbpy. (5) Analysis based on Marcus theory showed that the electronic coupling term HィイD2rpィエD2 significantly depends on the electrostatic interaction, suggesting that the electrostatic interaction is important to the stereoselectivity in electron transfer reaction. (5) Photoderacemization of [Co(acac)ィイD23ィエD2] was carried out with Δ-[Ru(menbpy)ィイD23ィエD2]ィイD12+ィエD1 in acetonitrile-water under visible light irradiation. Quenching reactions and model reaction indicate that this reaction takes place through the oxidative quenching of Δ-ィイD1*ィエD1[Ru(menbpy)ィイD23ィエD2]ィイD12+ィエD1 by[Co(acac)ィイD23ィエD2]. (6) Electron transfer reaction was investigated with molecular mechanics, which shows that [Co(acac)ィイD23ィエD2] approaches [Ru(bpy)ィイD23ィエD2]ィイD12+ィエD1 along the CィイD23vィエD2 axis. Less