A visible-light-active ellagic acid-based titanium-oxo cluster for room temperature chemiresistive sensing

In this study, we synthesized a visible-light-active titanium-oxo cluster (TOC), i.e., [(CH₃)₂NH₂]⁺₂·[Ti₄L₂(OⁱPr)₁₀]²⁻ (1), based on ellagic acid (H₄L). The molecular structure of 1 was determined using single-crystal X-ray diffraction, revealing a cyclodextrin-like tetramer formed by four Ti₄ clusters and dimethylamine cations. Owing to its effective ligand-to-metal charge transfer, 1 exhibited good visible-light absorption ability and photocurrent response, as confirmed by ultraviolet–visible (UV–vis) spectroscopy and photoelectric testing. Structurally, the large number of uncoordinated oxygen sites in 1 serve not only as assembly sites but also as active sites for NO₂ detection. Moreover, 1 exhibited high NO₂ response and excellent selectivity under visible-light irradiation at room temperature. This research provides the first exploration of TOCs in gas sensing applications, expanding their potential beyond traditional uses.