Binding Modes of Salicylic Acids to Titanium Oxide Molecular Surfaces

A set of titanium oxide clusters (TOCs) comprised of 4 to 16 Ti atoms are synthesized with substituted salicylates (SSAs). The interfacial coordination environment of these SSA/Ti oxide hybrids are surveyed and found to be limited to four binding modes, with the bridging chelate mode being the most common one. The SSA-functionalized TOCs show strong visible light absorption properties. The contribution of the SSAs in the frontier orbitals of the TOCs are analyzed by using TD-DFT calculations based on the molecular geometries determined by X-ray diffraction. For TOCs of relatively high O/Ti ratio, the SSAs narrow the band gap of the TOCs by contributing solely to the HOMOs. Both binding modes and locations of the SSAs are important for the roles of SSAs in changing the HOMOs and thereby the absorption onsets.