Illuminating Light on D-π-A Zn Porphyrin Dyes for Efficient Solar to Chemical Fuel Generation

In this study, we design tunable D-pi-A porphyrin dyes, 2,1,3-benzo thiadiazole (BTD)-phenyl (LG-6) and 4-ethynyl thiophene (LG-5) as photosensitizers of Pt/TiO2 (PCT) for solar to chemical fuel generation. The PCT-LG5 and PCT-LG6 photocatalysts are evaluated for photoinduced hydrogen evolution and CO2 reduction to methanol. The PCT-LG6 at optimum (pH 1, 3, 7, and 10) reaction conditions produced hydrogen generation rate of 5.70 mmol. g- 1.h- 1 with a turnover number (TON) of 1140 and apparent quantum yield (AQY) of 13.8% under visible-light and remarkably high CO2 reduction reaction to methanol with a rate of 1.99, 1.38 mmol.g- 1.h- 1 for PCT-LG5, PCT-LG6 systems, respectively. The extended light absorptions (400-900 nm) of the photocatalysts is due to the correct pairing of functionalization between porphyrin and the anchoring group cyanoacrylic acid in LG-5 and carboxylic acid in LG-6. The cyanoacrylic group acts as an anchoring group in LG-5, inducing a red (bathochromic) shift in the Soret band and Q-bands, indicating effective intramolecular electronic charge transfer behavior alongside the implementation of strategies to enhance light harvesting properties which further substantiated by the density functional theory (DFT) studies.