Earth-abundant Zn-dipyrrin chromophores for efficient CO photoreduction.

The development of strong sensitizing and Earth-abundant antenna molecules is highly desirable for CO reduction through artificial photosynthesis. Herein, a library of Zn-dipyrrin complexes (-) are rationally designed via precisely controlling their molecular configuration to optimize strong sensitizing Earth-abundant photosensitizers. Upon visible-light excitation, their special geometry enables intramolecular charge transfer to induce a charge-transfer state, which was first demonstrated to accept electrons from electron donors. The resulting long-lived reduced photosensitizer was confirmed to trigger consecutive intermolecular electron transfers for boosting CO-to-CO conversion. Remarkably, the Earth-abundant catalytic system with and Fe-catalyst exhibits outstanding performance with a turnover number of >20 000 and 29.7% quantum yield, representing excellent catalytic performance among the molecular catalytic systems and highly superior to that of noble-metal photosensitizer Ir(ppy)(bpy) under similar conditions. Experimental and theoretical investigations comprehensively unveil the structure-activity relationship, opening up a new horizon for the development of Earth-abundant strong sensitizing chromophores for boosting artificial photosynthesis.