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

H₂O₂ 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 H₂O₂ 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 (H₂Pc(COOH)₈), achieving an unprecedented H₂O₂ 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 H₂O₂ generation on organic photocatalysts.