Repeated appearance and disappearance of localized surface plasmon resonance in 1.2 nm gold clusters induced by adsorption and desorption of hydrogen atoms.

Addition of an aqueous solution of NaBH4 to a dispersion of small (∼1.2 nm) gold clusters stabilized by poly(N-vinyl-2-pyrrolidone) (Au:PVP) induced a localized surface plasmon resonance (LSPR) absorption for a certain period of time while maintaining the cluster size. The duration of the LSPR band could be lengthened by increasing the NaBH4 concentration and shortened by increasing the concentration of dissolved O2, and the LSPR band could be made to appear and reappear repeatedly. The appearance of the LSPR band is explained by the electron donation to the Au core from the adsorbed H atoms that originate from NaBH4, whereas its disappearance is ascribed to the removal of H atoms by their reaction with O2. These results suggest that the transition between the metallic and non-metallic electronic structures of the Au clusters can be reversibly induced by the adsorption and desorption of H atoms, which are electronically equivalent to Au.