Bridging Platinum and Palladium to Bipyridine-Annulated Perylene for Light-Driven Hydrogen Evolution

In this work, we present two bipyridine-annulated perylenetetracarboxylicester (P-L) photocatalysts with PtCl2 andPdCl(2). X-ray photoelectron spectroscopy showed that theirbinding energies match precisely the binding energies of the respectiveM-(bpy)-Cl-2 complexes. Cyclic voltammetry measurements ofthe complexes displayed additional reduction potentials upon metalinsertion. Light-driven catalysis demonstrated that both compoundsare catalytically active, with P-Pt outcompeting P-Pd with a TON of 186 over 48 h in the presence of ascorbicacid (P-Pd: 50). Mercury poisoning experiments were carriedout to validate the catalytically competent component. Almost quantitativequenching of the catalytic turnover was observed for P-Pd, whereas the hydrogen production rate remained unaffected for P-Pt, making it a photocatalyst that contains the structurePtN<^>NCl2 and nonetheless operates without a second noblemetal nucleus or a separate photosensitizer under visible light. Time-resolved(fs and ns) spectroscopy on P-L and P-Pt yields insights into the light-induced intramolecular processes.In P-Pt, we observed that both (IL)-I-1 (400 nm)and (MLCT)-M-1 (500 nm) excitation leads to intersystem crossingwith a solvent polarity-dependent distribution between (MLCT)-M-3 and (IL)-I-3, where the (IL)-I-3 population increasesin ACN vs DCM, indicating that in aqueous catalytic samples, the (IL)-I-3 state plays a major role in the catalytic process.