Uphill Photooxidation of NADH Analogues by Hexyl Viologen Catalyzed by Zinc Porphyrin-Linked Fullerenes

In the absence of oxygen, the photolytically generated C 60 •- moiety in ZnP •+ −C 60 •- and ZnP •+ −H 2 P−C 60 •- radical ion pairs undergoes one-electron oxidation by hexyl viologen (HV 2+ ), whereas the ZnP •+ moiety is reduced by NADH analogues (1-benzyl-1,4-dihydronicotinamide and 10-methyl-9,10-dihydroacridine). Thus, both ZnP−C 60 and ZnP−H 2 P−C 60 donor−acceptor ensembles act in benzonitrile as efficient photocatalysts for the uphill oxidation of NADH analogues by HV 2+ . In the case of ZnP−C 60, the quantum yield of the photocatalytic reaction increases with increasing concentration of HV 2+ or an NADH analogue to reach a limiting value of 0.99. The limiting quantum yields of ZnP−C 60 and ZnP−H 2 P−C 60 agree well with the quantum yields of radical ion pair formation, ZnP •+ −C 60 •- and ZnP •+ −H 2 P−C 60 •-, 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 C 60 •- 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−C 60 ) in the overall photooxidation of an NADH analogue by HV 2+ . By contrast, the reactivity of the triad (i.e., ZnP−H 2 P−C 60 ) shows little effects upon admitting O 2 .