Development of 9,9-Disubstituted Fluorene-Based Di-Anchoring Photosensitizers for Highly Efficient Hydrogen Evolution

Abstract

New mono- and di-anchoring organic photosensitizers (PSs) with phenyl or triphenylamine (TPA) 9,9-substituted fluorene spacer and cyanoacrylic acid acceptor(s) were synthesized and evaluated for photocatalytic hydrogen generation from water. Their photophysical and electrochemical properties were studied, focusing on their correlation with photocatalytic performance. Di-anchoring PSs showed double the photocatalytic efficiency due to their lower LUMO level and two acceptor groups, facilitating efficient electron extraction, reducing aggregation on TiO2, enhancing light-harvesting abilities, and improving charge transfer. The PSs with substituted TPA adopted highly bulky molecular structures. The introduction of TPA groups specifically led to the suppression of charge transport resistance and enhancement of interfacial electron transfer. The TPA-substituted di-anchoring PS TPAF2-based photocatalytic system produced 1380 μmol of hydrogen over 47 hours under blue light, with a turnover number (TON) of 22660, a turnover frequency (TOFi) of 1067 h-1, an initial hydrogen production activity (activityi) of 666850 and an apparent quantum yield (AQYi%) of 11.418. The bulky TPA moieties rendered the PSs significantly photostable, as affirmed by their high hydrogen production efficiency over 257 hours of prolonged irradiation, generating 58.9 mL of hydrogen. This work presents a strategy for constructing efficient PSs for photocatalytic hydrogen generation from water.

Keywords: Di-anchoring · Triphenylamine · Photosensitizers ·Fluorene · Hydrogen Generation