Panchromatic Sensitization with Zn^II Porphyrin-Based Photosensitizers for Light-Driven Hydrogen Production

Three molecular photosensitizers (PSs) with carboxylic acid anchors for attachment to platinized titanium dioxide nanoparticles were studied for light-driven hydrogen production from a fully aqueous medium with ascorbic acid (AA) as the sacrificial electron donor. Two zinc(II) porphyrin (ZnP)-based PSs were used to examine the effect of panchromatic sensitization on the photocatalytic H₂ generation. A dyad molecular design was used to construct a difluoro boron-dipyrromethene (bodipy)-conjugated ZnP PS (ZnP-dyad), whereas the other one featured an electron-donating diarylamino moiety (YD2-o-C8). To probe the use of the ZnP scaffold in this particular energy conversion process, an organic PS without the ZnP moiety (Bodipy-dye) was also synthesized for comparison. Ultrafast transient absorption spectroscopy was adopted to map out the energy transfer processes occurring in the dyad and to establish the bodipy-based antenna effect. In particular, the systems with YD2-o-C8 and ZnP-dyad achieved a remarkable initial activity for the production of H₂ with an initial turnover frequency (TOF_i ) higher than 300 h^-1 under white light irradiation. The use of ZnP PSs in dye-sensitized photocatalysis for the H₂ evolution reaction in this study indicated the importance of the panchromatic sensitization capability for the development of light absorbing PSs.