Identification of Crucial Photosensitizing Factors to Promote CO2‐to‐CO Conversion

Abstract The sensitizing ability of a catalytic system is closely related to the visible‐light absorption ability, excited‐state lifetime, redox potential, and electron‐transfer rate of photosensitizers (PSs), however it remains a great challenge to concurrently mediate these factors to boost CO 2 photoreduction. Herein, a series of Ir(III)‐based PSs ( Ir‐1 – Ir‐6 ) were prepared as molecular platforms to understand the interplay of these factors and identify the primary factors for efficient CO 2 photoreduction. Among them, less efficient visible‐light absorption capacity results in lower CO yields of Ir‐1 , Ir‐2 or Ir‐4 . Ir‐3 shows the most efficient photocatalytic activity among these mononuclear PSs due to some comprehensive parameters. Although the K obs of Ir‐3 is ≈10 times higher than that of Ir‐5 , the CO yield of Ir‐3 is slightly higher than that of Ir‐5 due to the compensation of Ir‐5 ’s strong visible‐light‐absorbing ability. Ir‐6 exhibits excellent photocatalytic performance due to the strong visible‐light absorption ability, comparable thermodynamic driving force, and electron transfer rate among these PSs. Remarkably, the CO 2 photoreduction to CO with Ir‐6 can achieve 91.5 μmol, over 54 times higher than Ir‐1 , and the optimized TON C‐1 can reach up to 28160. Various photophysical properties of the PSs were concurrently adjusted by fine ligand modification to promote CO 2 photoreduction.