Selective hybridization of organic dyes with CuSCN during its electrochemical growth

Nine different organic dyes have been used for electrochemical self-assembly (ESA) of CuSCN/dye hybrid thin films. One of these dyes was added to the bath for cathodic electrodeposition of CuSCN, containing Cu²⁺ and SCN⁻ ions in ethanol. While anionic xanthene dyes having a carboxylic acid group were not loaded into the film, resulting in colorless CuSCN thin films with unchanged morphology and crystal orientation with the c-axis of β-CuSCN perpendicular to the substrate, all the other dyes were loaded to yield colorful CuSCN/dye hybrid thin films with specific hybrid nanostructures and preferential orientation to lay down the c-axis in parallel with the substrate. The hard and soft, acid and base (HSAB) principle nicely explains the successful ESA of dyes having a soft Lewis basic –NCS group for stable coordination to soft Lewis acidic Cu(I) sites of CuSCN. This further explains why the xanthene dyes, having hard Lewis basic carboxylate, did not coordinate with the CuSCN during electrodeposition, but did yield ESA with hard Lewis acidic ZnO in our previous studies. On the other hand, partial replacement of Cu⁺ ions of CuSCN with cationic dyes was found to be another efficient loading mechanism of ESA. These two mechanisms were confirmed by ESA in bath containing excess SCN⁻ and Cu²⁺ respectively.