Molecularly engineered porphyrin photosensitizers featuring multi-anchoring and alkoxy modifications for robust photocatalytic hydrogen production

Abstract

In this work, we introduce a new generation of porphyrin-based photosensitizers (PSs), PoTA1–PoTA3, each strategically engineered with dual anchoring groups—4-ethynylbenzoic acid, 3-ethynylbenzoic acid, or 5-ethynylthiophene-2-carboxylic acid—at the meso-position of the porphyrin macrocycle, and further functionalized with long-chain alkyloxy substituents. This dual-modification strategy not only suppresses undesirable charge recombination but also reduces aggregation on TiO₂ surfaces. Notably, PoTA3, featuring the 5-ethynylthiophene-2-carboxylic acid moiety, exhibits a dramatically redshifted and broadened absorption profile, enabling superior solar spectrum utilization. Under blue light irradiation, the PoTA3-based system achieves a remarkable apparent quantum yield (AQY) of 8.3%, an initial hydrogen evolution rate of 485 mmol g−1 h−1, and an exceptional turnover number (TON) of 27,858 in aqueous media—substantially outperforming both PoTA1 and PoTA2. More notably, both PoTA1 and PoTA3 exhibit remarkable performance under white light irradiation (AQY% = 5.5% and 6.8%, respectively), significantly outperforming the benchmark YD2-o-C8 (AQY% = 4.07%) under identical operating conditions. The synergistic effect of enhanced light harvesting, minimized aggregation, and optimized HOMO and LUMO electron density distributions in PoTA1 and PoTA3 translates to both high efficiency and robust operational stability. These findings create a flexible molecular engineering platform for the next generation of solar-to-hydrogen conversion systems. Our approach opens the door to designing better photosensitizers, which could lead to major improvements in producing hydrogen from water using sunlight. (Figure presented.)