Photocatalytic CO₂ Reduction Mediated by Electron Transfer via the Excited Triplet State of Zn(II) Porphyrin

Abstract

A porphyrin/rhenium complex dyad, <b>ZnP-phen=Re</b>, in which the 2-position of the 1,10-phenanthroline (phen) of <i>fac</i>-Re(phen)(CO)₃Br is directly connected with the <i>meso</i>-position of zinc(II) porphyrin, showed phosphorescence from the zinc porphyrin part under Ar, even at room temperature. The phosphorescence was efficiently quenched by 1,3-dimethyl-2-phenyl-2,3-dihydro-1<i>H</i>-benzo[<i>d</i>]imidazole (BIH) used as an electron donor, under Ar, with the Stern-Volmer constant <i>K</i>_SV = 180 000 M^-1, indicating that the quantitative photoinduced electron transfer occurred from BIH to the excited triplet state (T₁) of <b>ZnP-phen=Re</b>. The system affords CO with a high turnover number (>1300) and >99.9% CO selectivity in the photocatalytic CO₂ reduction.