A benzofuran[b]-fused BODIPY as an efficient sensitizer for photocatalytic hydrogen production

A benzofuran[b]-fused BODIPY-based photosensitizer type 1 was synthesized for the first time by using an unsymmetrical π-conjugated system composed of benzofuro[3,2-b]pyrrole and pyrromethene units with anchoring groups that are bound to TiO2. Dye 1 has an intense absorption band in the visible to red region with a λmax value of 605 nm and a molar extinction coefficient (ε) of 1.07 × 105 M−1 cm−1. Benzofuran fusion at the b-band of the pyrrole unit causes stabilization of both the highest occupied molecular orbital (HOMO) energy levels and lowest unoccupied molecular orbital (LUMO) energy levels, endowing it with long-term stability. After deposition on the P25/Pt photocatalyst to produce P25/Pt/1, the photocatalytic activity was investigated in the presence of ascorbic acid as a sacrificial agent in aqueous phosphate buffer solution (pH 3.6) under irradiation with λ > 400 nm using a 300 W Xe lamp at 100 mW cm−2 light intensity. After light irradiation for 10 h, the system achieved a remarkable catalytic activity for H2 production with a turnover number (TON) value of 11 700. The dye grafted onto TiO2 remains almost unchanged even after photoirradiation for 30 h. The electron dynamics between the dye and TiO2 were investigated by time-resolved fluorescence spectroscopy, photocurrent measurements and electrochemical impedance spectroscopy. The apparent quantum yields (AQYs) were evaluated by monitoring H2 production for each monochromatic light irradiation. The values of AQY for P25/Pt/1 were 3.80% and 3.72% at λ = 420 nm and 600 nm, respectively, indicating an excellent light harvesting capability as a sensitizer.