Biruthenium Complexes for Semiconductor Functionalization: Insights into Surface Binding and Charge Separation on TiO 2 (110)

We investigated the adsorption and electronic properties of a cyanide-bridged biruthenium complex on rutile TiO2 (110) surfaces using X-ray photoelectron spectroscopy (XPS) and density functional theory (DFT) calculations. This dimer complex forms a stable monolayer on the surface, with a bidentate binding through deprotonated carboxylic acid groups, similar to its monomeric counterparts. DFT calculations of the [II,II] complex suggest that the energy of the lowest unoccupied molecular orbital (LUMO) overlaps with the conduction band of TiO2, facilitating electron injection from the excited state of the complex. For the mixed-valence complex, both spectroscopy and DFT predict that the hole is localized on the distal ruthenium center, which is spatially separated from the TiO2 interface, potentially reducing the rate of back electron transfer. Our findings offer new insights into the interaction of biruthenium complexes with TiO2, contributing to the development of advanced molecular systems for light-driven applications such as dye-sensitized solar cells and photocatalysis.