Synergistic dual-electron acceptors in linear conjugated polymers for boosting photocatalytic hydrogen evolution

Abstract

A conjugated polymer photocatalyst containing dual-electron acceptor units, dibenzo[b,d]thiophene sulfone (DBS) and 2,1,3-benzothiadiazole (BT), known as PBT, has been synthesized for its strong electron-withdrawing abilities and structural flexibility. However, the inherent hydrophobicity of PBT leads to significant particle aggregation, hindering colloidal stability and electron transfer to protons. To overcome these limitations, fluorine and ethylene glycol (EG) groups are strategically incorporated into the BT unit to enhance molecular planarity and hydrophilicity, respectively. This molecular engineering effectively suppresses exciton and charge recombination, facilitating efficient charge separation and extraction. Comprehensive spectroscopic analyses—including time-resolved photoluminescence (Tr-PL) and transient absorption spectroscopy (TAS)—reveal that EG-functionalized polymers exhibit prolonged exciton lifetimes and strong photoinduced absorption at early timescales, indicating both suppressed non-radiative recombination and effective charge generation. Importantly, these modifications enable rapid charge separation and transfer with more efficient electron extraction to protons, mitigating charge accumulation within aggregated domains. Among the modified polymers, 4EG-PBTz-F, with di-fluoro substituents and tetra-ethylene glycol groups, achieves the highest hydrogen evolution rates of 15.476 mmol g⁻¹ and 3.095 mmol g⁻¹ h⁻¹ with a 3 wt% Pt co-catalyst. These results highlight the effectiveness of dual-electron acceptor design and interfacial control, offering a multi-faceted design strategy in photocatalytic hydrogen evolution systems.