Uphill photooxidation of NADH analogues by hexyl viologen catalyzed by zinc porphyrin-linked fullerenes

Shunichi Fukuzumi, Hiroshi Imahori, Ken Okamoto, Hiroko Yamada, Mamoru Fujitsuka, Osamu Ito, Dirk M. Guldi

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In the absence of oxygen, the photolytically generated C60.- moiety in ZnP.+-C60.- and ZnP.+-H2P-C60.- radical ion pairs undergoes one-electron oxidation by hexyl viologen (HV2+), whereas the ZnP.+ moiety is reduced by NADH analogues (1-benzyl-1,4-dihydronicotinamide and 10-methyl-9,10-dihydroacridine). Thus, both ZnP-C60 and ZnP-H2P-C60 donor-acceptor ensembles act in benzonitrile as efficient photocatalysts for the uphill oxidation of NADH analogues by HV2+. In the case of ZnP-C60, the quantum yield of the photocatalytic reaction increases with increasing concentration of HV2+ or an NADH analogue to reach a limiting value of 0.99. The limiting quantum yields of ZnP-C60 and ZnP-H2P-C60 agree well with the quantum yields of radical ion pair formation, ZnP.+-C60.- and ZnP.+-H2P-C60.-, respectively. In the presence of oxygen, the lifetimes of the radical ion pairs are, however, markedly reduced because of an oxygen-catalyzed back electron transfer process between C60.- and ZnP.+. Such an impact on the radical ion pair lifetime consequences a significant decrease in the photocatalytic reactivity of the dyad (i.e., ZnP-C60) in the overall photooxidation of an NADH analogue by HV2+. By contrast, the reactivity of the triad (i.e., ZnP-H2P-C60) shows little effects upon admitting O2.

Original languageEnglish
Pages (from-to)1903-1908
Number of pages6
JournalJournal of Physical Chemistry A
Issue number10
StatePublished - 14 Mar 2002


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