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 with the mono-metal systems. Thus, porphyrin metal alloy nanoclusters are potential candidates as a new type of artificial photosynthetic materials and photocatalysts.