Strong Visible-Light-Absorbing Cuprous Sensitizers for Dramatically Boosting Photocatalysis

Developing strong visible-light-absorbing (SVLA) earth-abundant photosensitizers (PSs) for significantly improving the utilization of solar energy is highly desirable, yet it remains a great challenge. Herein, we adopt a through-bond energy transfer (TBET) strategy by bridging boron dipyrromethene (Bodipy) and a Cu^I complex with an electronically conjugated bridge, resulting in the first SVLA Cu^I PSs (Cu-2 and Cu-3). Cu-3 has an extremely high molar extinction coefficient of 162 260 m^-1  cm^-1 at 518 nm, over 62 times higher than that of traditional Cu^I PS (Cu-1). The photooxidation activity of Cu-3 is much greater than that of Cu-1 and noble-metal PSs (Ru(bpy)₃ ²⁺ and Ir(ppy)₃ ⁺ ) for both energy- and electron-transfer reactions. Femto- and nanosecond transient absorption and theoretical investigations demonstrate that a "ping-pong" energy-transfer process in Cu-3 involving a forward singlet TBET from Bodipy to the Cu^I complex and a backward triplet-triplet energy transfer greatly contribute to the long-lived and Bodipy-localized triplet excited state.