Polymer Photocatalysts with Side Chain Induced Planarity for Increased Activity for Sacrificial Hydrogen Production from Water

Abstract

Conjugated polymers are promising materials for photocatalytic hydrogen evolution. However, most reported materials are not solution-processible, limiting their potential for large-scale application, for example as solution cast films. Flexible side-chains are commonly introduced to provide solubility, but these often impart unfavorable properties, such as hydrophobicity, which lowers photocatalytic activity. Here, computational predictions are employed to aid in the design of chloroform soluble polymer photocatalysts that show increased planarity through favorable intramolecular interactions. Using this approach, three conjugated polymer photocatalysts with identical poly(benzene-dibenzo[b,d]thiophene sulfone) backbones but different solubilizing side-chains on the benzene-ring are explored, i.e., tri(ethylene glycol), n-decyloxy, and n-dodecyl. These side-chain variations significantly alterr the properties of the polymers, specifically energy levels, optical gap, and wettability. The hydrophobic n-decyloxy functionalized polymer has a sacrificial hydrogen evolution rate of 17.0 µmol h−1 in suspension, while the hydrophilic tri(ethylene glycol) functionalized polymer is almost three times more active (45.4 µmol h−1). Conversely, no hydrogen evolution is observed for the purely alkyl side-chain (n-dodecyl) containing polymer due to the side-chain induced torsion of the backbone. A thin-film of the most active polymer exhibits a promising area-normalized sacrificial hydrogen evolution rate of 7.4 ± 0.3 mmol h−1 m−2 under visible light irradiation.