Chemically Modified Titanium-Oxo Clusters as Molecular Materials
Inspired by the widespread applications of TiO2, titanium-oxo clusters (TOCs) of the type [TixOy(OR)z] (OR = alkoxide) have attracted considerable attentions recently. In this thesis, new TOCs involving both heterogeneous metal doping and functional ligand modification, namely [Ti18Mn4O30(OEt)20Phen3] (Phen = 1,10- phenanthroline) and [LnTi6O3(OiPr)9(salicylate)6] (Ln = La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho and Er) have been synthesised and thoroughly characterised. One particular feature of the [Ti18Mn4O30(OEt)20Phen3] cluster is its capability for in situ self-assembly into hollow microparticles. A novel coating technology involving such in situ self-assembly has been demonstrated to fabricate multifunctional cotton fabrics in a single-step operation, producing spherical microparticles of 0.8 μm average diameter. These microparticles are firmly mounted on the underlying cotton substrate, imparting the coated surface with robust hydrophobicity, antibacterial activity and UV-blocking performance. For the [LnTi6O3(OiPr)9(salicylate)6] clusters, their isostructural features allow a systematic investigation of the influence of the paramagnetic Ln3+ ions on the NMR behaviour of the 1H and 13C nuclei in the peripheral ligands. Compared to conventional Ln3+-complexes, the ligands in these clusters are separated from the Ln3+ ions by oxo-Ti4+ linkages, and therefore experience a weaker paramagnetic influence. As a result, all the 1H and 13C resonance signals can be observed and unambiguously assigned, which makes the in-depth data analysis possible. The Ln-TOCs can also act as an excellent platform for investigating the photophysical interplay between the coordinated salicylate ligands, Ln3+ dopants and Ti4+ ions in TOCs. Both visible and near-infrared Ln3+-centred photoluminescence can be sensitised in solution, and their excitation bands all extend into the visible region up to 475 nm. An energy transfer mechanism involving the salicylate-to-Ti4+ charge-transfer state is proposed to account for the largely red-shifted excitation wavelengths, which is supported by both steady-state and time-resolved photoluminescence spectroscopic data.