Imbroglio at a photoredox-iron-porphyrin catalyst dyad for the photocatalytic CO$_{{2}}$ reduction

We have covalently connected the ruthenium trisbipyridine complex (bpyRu) as a photoredox module to an iron porphyrin catalyst (porFe) through an amido function for investigating the synergistic action to power the photocatalytic CO2 reduction. The electrochemical studies of the porFe-bpyRu dyad did not show any marked effect on the redox properties of the constitutive units. However, the photophysical properties of the porFe-bpyRu dyad point to the complete extinction of the photoredox module that undergoes ultrafast quenching processes with the porFe acolyte, the unavoidable dilemma in this type of molecular assemblies. Nevertheless, when exogenous bpyRu and a sacrificial electron donor were added to this dyad, we found that it exhibits much higher turnover number and selectivity towards CO2 photocatalytic reduction to CO than with the iron porphyrin analogue (porFe). Comprehensive analyses of the data suggest that this catalytic enhancement displayed by the dyad can be attributed to an interesting electron relay role played by the appended bpyRu moiety.