Controlling the Photofunctionality of a Polyanionic Heteroleptic Copper(I) Photosensitizer for CO2 Reduction Using Its Ion‐pair Formation with Polycationic Ammonium in Aqueous Media

A water-soluble trianionic heteroleptic copper(I) photosensitizer having four sulfonate groups (CuPS3- ) was found to afford the 1 : 2 ion-pair adduct with dicationic alkylammonium (hexamethonium) cations (HM2+ ) in aqueous media, leading to exhibit excellent photophysical and photocatalytic performances owing to the substantial suppression of water-derived non-radiative decay of the photoexcited state.