Metal and size effects on structures and photophysical properties of porphyrin-modified metal nanoclusters

Three-dimensional (3D) porphyrin monolayer protected metal nanoclusters (MPCs) have been prepared to examine the effects of metal (Au, Ag, Au–Ag alloy, Pd and Pt) and size (1–3 nm) on the structures and photophysical properties. The quenching rate constants of the porphyrin excited singlet state by the surfaces of mono-metal nanoclusters and gold nanoclusters with different diameters are virtually the same. In contrast, the quenching rate constant of the gold–silver alloy nanocluster is half that of the corresponding mono-metal clusters (i.e. Au or Ag). This reveals that interaction between the surface of the gold–silver alloy and the porphyrin excited singlet state is attenuated as compared wtih the mono-metal systems. Thus, porphyrin metal alloy nanoclusters are potential candidates as a new type of artificial photosynthetic materials and photocatalysts.