Effective photoreduction of CO2 catalyzed by oligo(p-phenylenes)

Photoreduction of CO2 to formic acid (HCO2-) and a small quantity of carbon monoxide (CO) can be achieved in N,N-dimethylformamide by using oligo(p- phenylenes) (OPP-n) as a photocatalyst and triethylamine (TEA) as a sacrificial electron donor under > 290 nm irradiation. Among OPP-n, p-terphenyl (OPP-3) and p-quaterphenyl (OPP-4) show high photocatalytic activity for the formation of HCO2-, in which the apparent quantum yields of HCO2- formation for OPP-3 and OPP-4 are 0.072 and 0.084, respectively. The laser flash photolysis and pulse radiolysis studies reveal that the photocatalysis initially start from the reductive quenching of the singlet state of OPP-n by TEA followed by the formation of the radical anion of OPP-n, OPP-n-, resulting in direct electron transfer from OPP-n- to CO2 molecules.