Ion Pairing of Cationic and Anionic Ir(III) Photosensitizers for Photocatalytic CO2 Reduction at Lipid–Membrane Surfaces

We synthesized an ion pair comprising cationic and anionic Ir(III) photosensitizers ([Ir1+][Ir2-]) for photocatalytic CO2 reduction and showed that the cationic component imparts stability, while the cyclometalating ligands in the anionic component ensure effective visible-light absorption. The triplet excited state of [Ir1+] is the key photoredox species in this system and is mainly generated through the transfer of triplet excitation energy from the anionic moiety due to Coulombic interactions and appropriate triplet energy alignment between the two ionic components. The positive photosensitization effect of ion pairing was demonstrated by photocatalytic CO2 reduction in cooperation with a Re(I) molecular catalyst incorporated into a vesicle membrane.