Charge Recognition\nin Ru(bpy)<sub>3</sub><sup>2+</sup> on a Metal Surface via Ultrahigh\nVacuum Tip-Enhanced Raman Spectroscopy

Ruthenium-based dye molecules hold great promise in the\nphotochemistry\nand electrochemistry research fields, ranging from photocatalysis\nand luminescence to thermal imaging and photodynamic therapy. However,\ndespite this exciting prospect, thermal sublimation and surface characterization\nof these molecules under ultrahigh vacuum (UHV) are rare. Here, we\nachieved successful thermal sublimation of tris(2,2′-bipyridine)­ruthenium(II)\n[Ru(bpy)<sub>3</sub><sup>2+</sup>] onto the Cu(100) surface and investigated\nthe surface decoration using scanning tunneling microscopy (STM) and\ntip-enhanced Raman spectroscopy (TERS). The experimental findings\nare complemented by density functional theory (DFT) and time-dependent\nDFT (TDDFT) calculations. Integrating experimental and theoretical\nanalyses facilitates the chemical characterization of Ru(bpy)<sub>3</sub><sup>2+</sup> molecules at the single-molecule level, encompassing\ntheir charged states and surface aggregation. Our analysis indicates\nno quenching of charge or significant charge transfer from the Cu\nsurface to the molecule’s core. These results here provide\nimportant chemical insight into ruthenium-based dye molecules essential\nfor photochemistry and electrochemistry-related applications.