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Intermolecular and Intracomplex Photoinduced Electron Transfer from Planar and Nonplanar Metalloporphyrins to p-Quinones

Authors

  • Masanori Kanematsu,

    1. Department of Material and Life Science, Graduate School of Engineering, Osaka University, ALCA (Japan) Science and Technology Agency (JST), 2–1 Yamada-oka, Suita, Osaka 565-0871 (Japan), Fax: (+81) 6-6879-7370
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  • Dr. Panče Naumov,

    1. Department of Material and Life Science, Graduate School of Engineering, Osaka University, ALCA (Japan) Science and Technology Agency (JST), 2–1 Yamada-oka, Suita, Osaka 565-0871 (Japan), Fax: (+81) 6-6879-7370
    2. Frontier Research Base for Global Young Researchers, Graduate School of Engineering, Osaka University, 2–1 Yamada-oka, Suita, Osaka 565-0871 (Japan)
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  • Prof. Dr. Takahiko Kojima,

    Corresponding author
    1. Department of Chemistry, Graduate School of Pure and Applied Sciences, University of Tsukuba, 1-1-1 Tennoudai, Tsukuba, Ibaraki 305-8571 (Japan)
    • Department of Chemistry, Graduate School of Pure and Applied Sciences, University of Tsukuba, 1-1-1 Tennoudai, Tsukuba, Ibaraki 305-8571 (Japan)
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  • Prof. Dr. Shunichi Fukuzumi

    Corresponding author
    1. Department of Material and Life Science, Graduate School of Engineering, Osaka University, ALCA (Japan) Science and Technology Agency (JST), 2–1 Yamada-oka, Suita, Osaka 565-0871 (Japan), Fax: (+81) 6-6879-7370
    2. Department of Bioinspired Science, Ewha Womans University, Seoul 120-750 (Korea)
    • Department of Material and Life Science, Graduate School of Engineering, Osaka University, ALCA (Japan) Science and Technology Agency (JST), 2–1 Yamada-oka, Suita, Osaka 565-0871 (Japan), Fax: (+81) 6-6879-7370
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Abstract

The rate constants of intermolecular photoinduced electron transfer from triplet excited states of metalloporphyrins to a series of p-benzoquinone derivatives in benzonitrile were determined to examine the effects of the driving force, the metal, and the conformational distortion of the porphyrin ring on the reorganization energies (λ) of electron transfer by laser flash photolysis. The λ values were evaluated from the determined rate constants on the basis of the Marcus theory of electron transfer. The λ values of planar metalloporphyrins, [Al(TPP)(PhCOO)] and [Zn(TPP)] (TPP2−=tetraphenylporphyrin dianion), are approximately the same, but they are 0.27 eV smaller than those of the corresponding nonplanar (saddle-distorted) metalloporphyrins [Al(DPP)(PhCOO)] and [Zn(DPP)] (DPP2−=dodecaphenylporphyrin dianion) when they are compared for the same driving force of photoinduced electron transfer. The axial ligand PhCOO of [Al(TPP)]+ and [Al(DPP)]+ was replaced by anthraquinone-2-carboxylate (AqCOO) to afford the electron donor–acceptor complexes [Al(TPP)(AqCOO)] and [Al(DPP)(AqCOO)], respectively. The X-ray crystal structure of [Al(TPP)(AqCOO)] revealed strong coordination of AqCOO to the Al3+ ion of [Al(TPP)]+ and the existence of π–π interactions between AqCOO and the porphyrin ring. In the case of the saddle-distorted [Al(DPP)(AqCOO)], however, the AqCOO moiety is nearly perpendicular to the porphyrin ring. The photodynamics of intracomplex photoinduced electron transfer from the singlet excited state of [Al(TPP)]+ and [Al(DPP)]+ to the AqCOO moiety were also examined in comparison with the intermolecular photoinduced electron-transfer reactions, and the determined rate constants were evaluated in light of the Marcus theory of electron transfer to reveal that the electron transfer is adiabatic in each case.

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