Near-infrared isomeric polymerized small molecular acceptors with thiophene-fused end groups for efficient photocatalytic hydrogen evolution

Abstract

Polymerized small molecular acceptors (PSMAs) now represent a class of promising organic photocatalysts for efficient photocatalytic hydrogen evolution due to their outstanding visible and near-infrared (NIR) light absorption. Although the isomerization strategy has been recognized as a simple yet effective method to modulate photovoltaic properties of PSMAs, the effects of isomerization on the performance of photocatalytic hydrogen evolution have never been reported so far. Herein, two isomeric thiophene-fused electron-withdrawing end groups with different fused sites are applied to construct isomeric PSMAs without π-linking units, namely PY-α-CPTCN and PY-β-CPTCN. Despite possessing identical molecular formulas, their π-conjugation and charge distribution are highly sensitive to the substitution patterns of thiophene-fused terminal units. Combined with experimental analysis and theoretical calculation, PY-α-CPTCN exhibits more efficient light absorption and charge transport than that of PY-β-CPTCN, ascribed to its stronger intramolecular π-conjugation effect. The resulting photocatalyst based on PY-α-CPTCN displays an average hydrogen evolution rate of 252.2 mmol g⁻¹ h⁻¹ under AM 1.5 G sunlight (100 mW cm⁻²), which is 3.2 times higher than that of PY-β-CPTCN with 79.7 mmol g⁻¹ h⁻¹. These results not only reveal the isomerization strategy as an effective method for the design of high-performance PSMA-based photocatalysts, but also emphasize the relevance between the intramolecular π-conjugation and photocatalytic properties.