Correlation between\nthe Molecular Properties of Semiconducting\nPolymers of Intrinsic Microporosity and Their Photocatalytic Hydrogen\nProduction

Increasing the interface\narea between organic semiconductor\nphotocatalysts\nand electrolyte by fabricating nanoparticles has proven to be an effective\nstrategy to increase photocatalytic hydrogen production activity.\nHowever, it remains unclear if increasing the <i>internal</i> interface by the introduction of porosity has as clear benefits\nfor activity. To better inform future photocatalyst design, a series\nof polymers of intrinsic microporosity (PIMs) with the same conjugated\nbackbone were synthesized as a platform to independently modulate\nthe variables of porosity and relative hydrophilicity through the\nuse of hydrophilic alcohol moieties protected by silyl ether protecting\ngroups. When tested in the presence of ascorbic acid and photodeposited\nPt, a strong correlation between the <i>wettable</i> porosity\nand photocatalytic activity was found, with the more wettable analogue\nof two polymers of almost the same surface area delivering 7.3 times\ngreater activity, while controlling for other variables. Transient\nabsorption spectroscopic (TAS) investigation showed efficient intrinsic\ncharge generation within 10 ps in two of the porous polymers, even\nwithout the presence of ascorbic acid or Pt. Detectable hole polarons\nwere found to be immediately extracted by added ascorbic acid, suggesting\nthe generation of reactive charges at regions readily accessible to\nelectrolyte in the porous structures. This study directs organic semiconductor\nphotocatalysts design toward more hydrophilic functionality for addressing\nexciton and charge recombination bottlenecks and clearly demonstrates\nthe advantages of wettable porosity as a design principle.