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

In this work, we present two bipyridine-annulated perylene tetracarboxylic ester (P-L) photocatalysts with PtCl2 and PdCl2. X-ray photoelectron spectroscopy showed that their binding energies match precisely the binding energies of the respective M(bpy)Cl2 complexes. Cyclic voltammetry measurements of the complexes displayed additional reduction potentials upon metal insertion. Light-driven catalysis demonstrated that both compounds are catalytically active, with P-Pt outcompeting P-Pd with a TON of 186 over 48 h in the presence of ascorbic acid (P-Pd: 50). Mercury poisoning experiments were carried out to validate the catalytically competent component. Almost quantitative quenching 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 structure PtN^NCl2 and nonetheless operates without a second noble metal 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 1IL (400 nm) and 1MLCT (500 nm) excitation leads to intersystem crossing with a solvent polarity-dependent distribution between 3MLCT and 3IL, where the 3IL population increases in ACN vs DCM, indicating that in aqueous catalytic samples, the 3IL state plays a major role in the catalytic process.