Delocalizing Excitation for Highly-Active Organic Photovoltaic Catalysts.

Localized excitation in traditional organic photocatalysts typically prevents the generation and extraction of photo-induced free charge carriers, limiting their activity enhancement under illumination. Here, we enhance delocalized photoexcitation of small molecular photovoltaic catalysts by weakening their electron-phonon coupling via rational fluoro-substitution. The optimized 2FBP-4F catalyst we develop here exhibits a minimized Huang-Rhys factor of 0.35 in solution, high dielectric constant and strong crystallization in the solid state. As a result, the energy barrier for exciton dissociation is decreased, and more importantly, polarons are unusually observed in 2FBP-4F nanoparticles (NPs). With the increased hole transfer efficiency and prolonged carrier lifetime highly related to enhanced exciton delocalization, the PM6:2FBP-4F heterojunction NPs at varied concentration exhibit much higher optimized photocatalytic activity (207.6~561.8 mmol h-1 g-1) for hydrogen evolution than the control PM6:BP-4F and PM6:2FBP-6F NPs, as well as other reported photocatalysts under simulated solar light (AM1.5G, 100 mW cm-2).