Visible-to-Near-Infrared Light-Driven Photocatalytic Hydrogen Production Using Dibenzo-BODIPY and Phenothiazine Conjugate as Organic Photosensitizer

A novel visible-to-near-infrared (visible-to-NIR) light-driven photocatalyst was prepared by loading a dibenzo-BODIPY-phenothiazine conjugate dye 1 as a panchromatic photosensitizer on hierarchical porous TiO2 (HPT) semiconductor. The sensitizer 1, which absorbed visible light at 638 and 440 nm with molecular extinction coefficients (epsilon) of 1.23 X 10(5) and 1.80 X 10(4) M-1 cm(-1), respectively, in THE due to the dibenzo-BODIPY and phenothiazine-based D-pi-A systems, respectively, showed panchromatic absorption up to 780 nm when deposited on the Pt/HPT photocatalyst to produce Pt/HPT500/1. The photocatalytic activities were investigated in the presence of ascorbic acid as a sacrificial agent in phosphate buffer solution under irradiation with lambda > 400 nm using a 300 W Xe lamp at 100 mW cm(-2) light intensity. After 10-h irradiation, the system achieved a remarkable catalytic activity for the production of H-2 with a turnover number (TON) value of 11100. The sustained activity was suggestive after two sequences of 10-h illumination-period, whereas we found somewhat decrease in the photoactivity for the third run, although a TON value of 5650 still remained. The apparent quantum yields were evaluated by monitoring H-2 production for each monochromatic light irradiation (lambda = 420, 530, 600, 670, 700, and 750 nm). They were found to be consistent with the absorption profile, proving the panchromatic hydrogen generation sensitized by 1. The active absorption band of dye 1 in the entire visible-to-NIR spectrum led to production of a dye-sensitized photocatalytic system with a light-to-fuel efficiency of 6.96% in the initial irradiation period. This study provides important information for the development of metal-free organic photosensitizers with a wide spectral response up to the NIR region for photocatalytic water splitting H-2 production.