Photochemical transformation of a perylene diimide derivative beneficial for the in situ formation of a molecular photocatalyst of the hydrogen evolution reaction

The photocatalytic splitting of water gains more and more attention as one of the most promising environmentally friendly approaches for the production of green hydrogen fuels. In this article, we report a peculiar feature of a carbazole derivative of the perylene diimide dye Cbz-PDI which forms in the presence of platinum salt and sunlight an efficient molecular photocatalyst of the hydrogen evolution reaction (HER). Such a photocatalyst (Cbz-PDCA-Pt-2) represents a unique group of organometallic platinum complexes with good sunlight absorption, satisfactory solubility, high stability and HER photoactivity. The in situ formation seems to be a convenient solution to the problems with the preparation, isolation and storage of such compounds. The best HER performance (in terms of the turnover number of 1900, decreased platinum usage and increased stability for longer than 3 days) was achieved when Cbz-PDCA-Pt-2 formed a mixture with Cbz-PDI and the molar percentage of platinum in the mixture did not exceed 10%. In such a system, Cbz-PDI facilitates charge separation and the storage of excitation energy due to the long lifetimes of its excited states observed as a result of thermally activated delayed fluorescence (TADF). The discovered photoreactivity of the perylene diimide derivative can hopefully open a new direction in the organometallic materials for use in molecular (photo)catalysis.