MAPPING ELECTRON-TRANSFER PATHWAYS IN A CHROMOPHORE-QUENCHER TRIAD

A comparative study of the photophysics of the four positional isomers (one trans and three cis) of the chromophore-quencher triad [Ru-II(dm b)(bpyCH(2)PTZ)(bpyCH(2)MV(2+))](4+) (dmb is 4,4'-dimethyl-2,2'-bipyri dine, bpyCH(2)PTZ is ethyl-4-(2,2'-bipyridin-4-yl)methyl)phenothiazine , and bpyCH(2)MV(2+) is bipyridin-4-yl)methyl)-1'-methyl-4,4'-bipyridi nium cation) has been undertaken, Following metal-to-ligand charge tra nsfer (MLCT) excitation by laser flash photolysis at 460 or 532, nm, t he redox-separated states [Ru-II(dmb)(bpyCH(2)PTZ(.+))(bpyCH(2)MV(.+)) ]4+ are formed rapidly (< 5 ns), Quenching of MLCT emission occurs wit h near unit efficiency for all four isomers. For the trans and cis3 is omers, formation of the redox-separated state is similar to 25% effici ent. For back electron transfer from -MV+ to -PTZ(+), Delta G0=-1.14 e V for all four isomers from electrochemical measurements and yet k(ET) varies from 4.5 x 10(6) to 8.7 x 10(6) s(-1) in acetonitrile at 25 de grees C.