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.
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 g(zz) values of the ESR spectra.
Fukuzumi
Shunichi
S
Department of Material and Life Science, Graduate School of Engineering, Osaka University, Suita, Osaka 565-0871, Japan. fukuzumi@ap.chem.eng.osaka-u.ac.jp
Okamoto
Ken
K
Yoshida
Yutaka
Y
Imahori
Hiroshi
H
Araki
Yasuyuki
Y
Ito
Osamu
O
D000577:Amides / Q000737:chemistry*; D004583:Electrons; D005296:Ferrous Compounds / Q000737:chemistry*; D006860:Hydrogen Bonding; D000075163:Metallocenes; D010777:Photochemistry; D011809:Quinones / Q000737:chemistry*
D000577:Amides; D005296:Ferrous Compounds; D000075163:Metallocenes; D011809:Quinones; C004998:ferrocene