Optical and electrochemical investigation on one-step three electron reduction of [Au^III(Salen)]Cl to Au(0): a comprehensive analysis

This work presents a comprehensive study of the UV–Visible and fluorescence properties, as well as the redox behavior of the [Au^III(Salen)]Cl complex in acetonitrile. The [Au^III(Salen)]⁺ complex exhibited intriguing fluorescence and phosphorescence characteristics on an indium tin oxide (ITO)-coated glass plate when excited at wavelength λ_exc ~ 260 nm, with fluorescence emission observed at λ_ems ~ 437 nm and phosphorescence at λ_ems ~ 520 nm. The origin of fluorescence emission was attributed to the intra-ligand charge transfer effect, commonly known as the "Push–Pull" effect. The electrochemical behavior of [Au^III(Salen)]⁺ on a glassy carbon electrode (GCE) revealed a remarkable one-step three-electron reduction process, leading to the reduction of [Au^III(Salen)]⁺ to Au(0). Furthermore, the reduction of [Au^I(Salen)]⁻ to Au(0) resulted in the removal of gold metal from the SalenH2 ligand. The electrochemical results suggested a mixed diffusion-adsorption redox process occurring at the GCE surface, indicating the involvement of both diffusion and adsorption during redox reactions. The cyclic voltammogram demonstrated the non-reversibility of the electrochemical redox reactions. Overall, the redox behavior of the [Au^III(Salen)]Cl complex proved to be intriguing, opening up avenues for further exploration and potential applications of this complex in various fields.