Surface-Enhanced Raman Scattering of Phenols and Catechols by a Molecular Analogue of Titanium Dioxide

Surface-enhanced Raman spectroscopy (SERS) of semiconducting TiO₂ was used for studying binding modes and surface reactions of molecules bound at the interface but is generally limited by low signal intensity and lack of authentic structural information. Here, we report a representative titanium-oxide cluster (TOC), i.e., Ti₁₇O₂₄(OC₃H₇)₂₀ (Ti₁₇), combines the benefits from both precise structures and intense SERS signals by providing a titania surface. According to the single-crystal X-ray diffraction analysis, phenols and catechols are vertically attached via σ-bonds to the certain sites of Ti₁₇. Ti₁₇ brings about much more intense Raman signals than the reference TiO₂ NPs, leading to 10^-5-10^-6 M analyte detection (enhancement factors are 10³-10⁵). The contributions of focusing effect, CHEM effect and resonance mechanism, all of which are found responsible for the higher SERS activity of Ti₁₇ than the reference TiO₂ NPs, in the SERS by Ti₁₇ are quantitatively analyzed. This study suggests SERS by TOCs may be promising for detection purposes and structural studies of environmentally and catalytically relevant molecules with fewer assumptions regarding molecular structures or binding mechanisms.