Intermolecular and intracomplex photoinduced electron transfer from planar and nonplanar metalloporphyrins to p-quinones

Masanori Kanematsu, Pance Naumov, Takahiko Kojima, Shunichi Fukuzumi

    Research output: Contribution to journalArticle

    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)] (TPP 2-=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)] (DPP 2-=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 Al 3+ 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. Photodynamics: The intermolecular, photoinduced electron-transfer properties of planar and nonplanar Al III porphyrins as electron donors were revealed by comparison with Zn II porphyrins. The photodynamics of intracomplex, photoinduced electron transfer from planar and nonplanar Al III porphyrins to the anthraquinone moieties (see figure) were examined in comparison with the intermolecular, photoinduced electron-transfer reactions.

    Original languageEnglish (US)
    Pages (from-to)12372-12384
    Number of pages13
    JournalChemistry - A European Journal
    Volume17
    Issue number44
    DOIs
    StatePublished - Oct 24 2011

    Fingerprint

    Metalloporphyrins
    Quinones
    Electrons
    Porphyrins
    Rate constants
    Anthraquinones
    Excited states
    Photolysis

    Keywords

    • electron transfer
    • photochemistry
    • photosynthesis
    • pi interactions
    • redox chemistry

    ASJC Scopus subject areas

    • Chemistry(all)

    Cite this

    Intermolecular and intracomplex photoinduced electron transfer from planar and nonplanar metalloporphyrins to p-quinones. / Kanematsu, Masanori; Naumov, Pance; Kojima, Takahiko; Fukuzumi, Shunichi.

    In: Chemistry - A European Journal, Vol. 17, No. 44, 24.10.2011, p. 12372-12384.

    Research output: Contribution to journalArticle

    Kanematsu, Masanori ; Naumov, Pance ; Kojima, Takahiko ; Fukuzumi, Shunichi. / Intermolecular and intracomplex photoinduced electron transfer from planar and nonplanar metalloporphyrins to p-quinones. In: Chemistry - A European Journal. 2011 ; Vol. 17, No. 44. pp. 12372-12384.
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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)] (TPP 2-=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)] (DPP 2-=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 Al 3+ 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. Photodynamics: The intermolecular, photoinduced electron-transfer properties of planar and nonplanar Al III porphyrins as electron donors were revealed by comparison with Zn II porphyrins. The photodynamics of intracomplex, photoinduced electron transfer from planar and nonplanar Al III porphyrins to the anthraquinone moieties (see figure) were examined in comparison with the intermolecular, photoinduced electron-transfer reactions.",
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    AU - Fukuzumi, Shunichi

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    KW - electron transfer

    KW - photochemistry

    KW - photosynthesis

    KW - pi interactions

    KW - redox chemistry

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