Unveiling the Role of Excited‐State Dipole Moment: Governing Non‐Sacrificial H ₂ O ₂ Generation on Porphyrin Photocatalysts

Abstract

Abstract H 2 O 2 production via the simultaneous oxygen reduction reaction (ORR) and water oxidation reaction (WOR) on organic photocatalysts theoretically achieves 100% atom economy. However, the charge separation and transfer mechanism in such organic systems remains poorly understood, especially as organic molecular designs based on ground‐state dipole moments (µ g ) often fail to predict photocatalytic behavior. Here, we synthesize a series of carboxyl‐modified tetraphenylporphyrin supramolecular photocatalysts (TPP‐(COOH) n , where n  = 1∼4, 8) to investigate the structure‐activity relationship. The H 2 O 2 generation activity follows the order TPP‐(COOH) 2  < TPP‐(COOH) < TPP‐(COOH) 3  < TPP‐(COOH) 8  < TPP‐(COOH) 4 , increasing with the excited‐state dipole moment (µ e ) rather than the traditionally considered µ g or number of ‐COOH groups. The µ e , influenced by O 2p‐band center shifts from carboxyl substitution, is demonstrated to govern the charge separation and transfer via an internal electric field. Moreover, exciton dissociation studies indicated that low‐dielectric TPP‐(COOH) n exhibits notably prolonged excitonic lifetimes (ca. 5 ns), making µ e the key activity determinant. Based on this insight, we designed a high‐µ e phthalocyanine supramolecular photocatalyst (H 2 Pc(COOH) 8 ), achieving an unprecedented H 2 O 2 production rate of 58 mM·h −1 ·g −1 and a quantum efficiency (QE) of 18.7% at 420 nm. This study establishes µ e as a predictive parameter for H 2 O 2 generation on organic photocatalysts.