Combining Metal Nanoparticles with an Ir(III) Photosensitizer

We report on a new photocatalytic system that consists of an iridium-based photosensitizer that has been encapsulated into the pores of the metal-organic framework (MOF) MIL-101, which have then been loaded with metal nanoparticles. Loading with Ni leads to substantially increased photocatalytic hydrogen evolution rates, whereas loading with Pt and Pd leads to only a small increase or none at all, respectively. These experimental findings triggered us to theoretically study the combination of the photo sensitizer and metal cluster in detail. Time-dependent density functional theory calculations with an optimally tuned range-separated hybrid functional show that the optical excitations of systems, in which the iridium-based photo sensitizer is combined with a metal cluster, involve a pronounced charge transfer from the metal to the photosensitizer. Density functional calculations show that the binding energy between the photosensitizer and the metal cluster is considerably larger for Ni than for Pd and Pt.