Self-Assembly Driven Modulation of Photocatalytic H2O2 Activity in Acridine-Based Derivatives

Abstract Self-assembly provides a powerful strategy for regulating the photophysical and photocatalytic properties of π-conjugated organic molecules through controlled intermolecular organization. Herein, we demonstrate that molecular aggregation can either suppress or activate photocatalysis, depending on the structural and solubility properties of the catalyst. Two organic photocatalysts, Acr-1 and Acr-2, with distinct affinities toward water, exhibit markedly different H2O2 generation behavior upon self-assembly. Hydrophilic Acr-1 efficiently produces H2O2 in aqueous 3-(N-morpholino)propanesulfonic acid (MOPS) solution in its monomeric state, whereas self-assembly suppresses its photocatalytic activity. In striking contrast, Acr-2, which is inactive in its monomeric state, becomes photocatalytically active upon self-assembly. Spectroscopic investigations indicate that aggregation in Acr-2 suppresses nonradiative deactivation pathways and promotes productive photochemical processes, thereby enabling H2O2 generation. The resulting supramolecular assemblies remain stable under continuous irradiation for up to 4 h while retaining their photocatalytic activity. Scavenger experiments combined with spectroscopic analyses further elucidate the involvement of reactive intermediates in H2O2 generation. These findings establish aggregation state as an important molecular parameter for regulating photocatalytic function and demonstrate that supramolecular self-assembly can be harnessed to switch and maintain solar-driven H2O2 generation in organic photocatalyst.