Photochemically controlled electrochemical deposition and dissolution of Ag⁰ nanoclusters on Au electrode surfaces

A photoisomerizable thiolated nitrospiropyran SP, (1a), monolayer is assembled on a Au electrode by the primary deposition of thiolated nitromerocyanine isomer 1b as a monolayer on the electrode, followed by the irradiation of the surface with visible light, λ > 475 nm. The surface coverage of nitrospiropyran units (1a) on the electrode is 2 × 10 ^-10 mole cm^-2. Irradiation of the electrode with UV light, 320 nm < λ < 360 nm, results in the nitromerocyanine, MR, monolayer on the electrode that binds Ag⁺ ions to the phenolate units. The Ag⁺ ions associated with the MR monolayer undergo cyclic reduction to surface-confined Ag⁰ nanoclusters, and reoxidation and dissolution of the Ag⁰ nanoclusters to Ag⁺ ions associated with the monolayer are demonstrated. The electron-transfer rate constants for the reduction of Ag⁺ to Ag⁰ and for the dissolution of Ag⁰ were determined by chronoamperometry and correspond to k _et^red = 12.7 s^-1 and k_et ^DX = 10.5 s^-1, respectively. The nanoclustering rate was characterized by surface plasmon resonance measurements, and it proceeds on a time scale of 10 min. The size of the Ag⁰ nanoclusters is in the range of 2 to 20 nm. The electrochemically induced reduction of the MR-Ag ⁺ monolayer to the MR-Ag⁰ surface and the reoxidation of the MR-Ag⁰ surface control the hydrophilic-hydrophobic properties of the surface. The advancing contact angle of the MR-Ag⁰-functionalized surface is 59°, and the contact angle of the MR-Ag⁺- monolayerfunctionalized surface is 74°. Photoisomerization of the Ag ⁰-MR surface to the Ag⁰-SP state, followed by the oxidation of the Ag⁰ nanoclusters, results in the dissolution of the Ag⁺ ions into the electrolyte solution.