Hydrogen-Mediated Electron Doping of Gold Clusters As Revealed by In Situ X‑ray and UV–vis Absorption Spectroscopy

We previously reported that small (∼1.2 nm) gold clusters stabilized by poly­(N-vinyl-2-pyrrolidone) (Au:PVP) exhibited a localized surface plasmon resonance (LSPR) band at ∼520 nm in the presence of NaBH4. To reveal the mechanism of this phenomenon, the electronic structure of Au:PVP during the reaction with NaBH4 in air was examined by means of in situ X-ray absorption spectroscopy at Au L3-edge and UV–vis spectroscopy. These measurements indicated that the appearance of the LSPR band is not associated with the growth in size but is ascribed to electron doping to the Au sp band by the adsorbed H atoms.