Supporting Information Hot adsorbate-induced retardation of the internal thermalization of nonequilibrium electrons in adsorbate-covered metal nanoparticles

We use "soft" surface science approach to prepare the samples, that permit the investigation of the metal/molecule interface by transient absorption spectroscopy. The overall structure of the sample consists of a mesoporous nanostructured metal oxide film, that acts as a host for the adsorbate-covered metal nanoparticles (see Fig. S1). The three dimensional nanostructured samples were prepared by wet-grafting of initial Au NPs of 1.7± 0.4 nm in diameter derivatized with mercapto succinic acid (MSA) into the pores of a TiO2 mesoporous thin film. Before the insertion of gold NPs, the TiO2 nanocrystalline films exhibit a porosity of 60 % with an average pore size of 20 nm (see Fig. S2). The capping molecules to stabilize the small gold nanoparticles were chosen in order to be able to form a molecular bridge between TiO2 and Au nanoparticles. MSA appears as good candidate for this purpose. Aqueous solution of primary 1.7 nm gold NPs were synthesized by NaBH4 reduction of AuCl4 in a mixture of water and methanol. The synthesis includes five consecutive washing and centrifugation steps with pure methanol. This sequence ensures the removal of inorganic ions. The solvent excess was evaporated at temperatures below 40°C and a pressure lower than 5⋅10 Torr for 12 h. The core size of the resulting particles exhibited an average diameter of (1.7 ± 0.4) nm. Carboxylates groups of mercapto succinic acid act as anchors to attach the 1.7 nm Au NPs into the pores of TiO2 film. Indeed, carboxylate groups are known to bind strongly onto TiO2 surface via a bidentate binuclear coordination mode.