Portal de Periódicos da CAPES

Effects of Hydrogen Bonding on Metal Ion-Promoted Intramolecular Electron Transfer and Photoinduced Electron Transfer in a Ferrocene-Quinone Dyad with a Rigid Amide Spacer

2002; American Chemical Society; Volume: 125; Issue: 4 Linguagem: Inglês

10.1021/ja026441v

1943-2984

Shunichi Fukuzumi, Ken Okamoto, Yutaka Yoshida, Hiroshi Imahori, Yasuyuki Araki, Osamu Ito,

Porphyrin and Phthalocyanine Chemistry

A ferrocene-quinone dyad (Fc-Q) with a rigid amide spacer and Fc-(Me)Q dyad, in which the amide proton acting as a hydrogen-bonding acceptor is replaced by the methyl group, are employed to examine the effects of hydrogen bonding on both the thermal and the photoinduced electron-transfer reactions. The hydrogen bonding of the semiquinone radical anion with the amide proton in Fc-Q•- produced by the electron-transfer reduction of Fc-Q is indicated by the significant positive shift of the one-electron reduction potential of Fc-Q. The hyperfine coupling constants of Fc-Q•- also indicate the existence of hydrogen bonding, agreeing with those predicted by the density functional calculation. The hydrogen-bonding dynamics in the photoinduced electron transfer from the ferrocene (Fc) to the quinone moiety (Q) in Fc-Q have been successfully detected in the femtosecond laser flash photolysis experiments. Thermal intramolecular electron transfer from Fc to Q in Fc-Q and Fc-(Me)Q also occurs efficiently in the presence of metal ions in acetonitrile at 298 K. The hydrogen bond formed between the semiquinone radical anion and the amide proton in Fc-Q results in remarkable acceleration of the rate of metal ion-promoted electron transfer as compared to the rate of Fc-(Me)Q in which hydrogen bonding is prohibited. The metal ion-promoted electron-transfer rates are well correlated with the binding energies of superoxide ion-metal ion complexes, which are derived from the gzz values of the ESR spectra.