Attention has been paid to titanium-oxo clusters (TOCs) modified with functional molecules, because they can be considered as model systems for dye-sensitized titanium oxides in terms of their information in structures and electron transfer. We select 9-anthracenecarboxylate (9-AC) as a photoactive ligand and prepare two model compounds, [Ti6O6(O(i)Pr)6(9-AC)6] (1) and [Ti6O4(O(i)Pr)6(cat)4(9-AC)2] (2) (where cat = catecholate). Structures of the TOCs and the dye-TOC linkage are characterized by single-crystal analysis. Solvent-induced fluorescence change is observed for the cluster solution, and the fluorescence can be turned off by irradiating and on by oxygen bubbling. Photoinduced Ti(III) is responsible for the fluorescence extinction. The photocurrent conversion property of the clusters is examined by use of a three-electrode cell with cluster-coated indium tin oxide (ITO) electrodes. The results indicate that 9-AC is an effective photosensitizer and cluster 1 shows higher photocurrent intensity for its multiantenna structure in comparison with that of 2. Density of states for cluster 1 is calculated, in which the discrete energy bands of Ti6O24 include a number of new energy levels for the contribution of 9-AC molecules.

Titanium-oxo-clusters (TOCs), [TiO(OPr)(Cat)(BA)] (1) and [TiMO(OEt)(Cat)(BA)] (M = Co, Mn, Ni, 2-4; HCat = catechol, HBA = benzoic acid) are prepared in one step in an in situ solvothermal synthesis. Cluster structures of 2-4 can be considered as two 1 moieties merged together by two transition metal atoms. Unlike most TOCs with sphere-like structures, clusters 2-4 feature a unique single layered structure. They are not only transition metal doped TOCs but also charge transfer (CT) TOCs, CT from Cat to the TiO cluster core. Photoelectrodes were prepared by dipping the solution of clusters on a porous TiO substrate. Photocurrent response properties of the electrodes were studied in comparison with those of the electrodes of non-metal doped 1 and the non-Cat coordinated Ti cluster. The results showed that the photocurrent densities of metal doped clusters are higher than that of non-doped clusters and the highest photocurrent density was found for the redox active Co(ii) doped cluster. Charge transfer also plays an effective role in photocurrent conversion under visible light irradiation.

Two benzene dicarboxylate (BDC) and salicylate (SAL) substituted titanium-oxo-clusters, Ti13O10(o-BDC)4(SAL)4(O(i)Pr)16 (1) and Ti13O10(o-BDC)4(SAL-Cl)4(O(i)Pr)16 (2), are prepared by one step in situ solvothermal synthesis. Single crystal analysis shows that the two Ti13 clusters take a paddle arrangement with an S4 symmetry. The non-compact (non-sphere) structure is stabilized by the coordination of BDC and SAL. Film photoelectrodes are prepared by the wet coating process using the solution of the clusters and the photocurrent response properties of the electrodes are studied. It is found that the photocurrent density and photoresponsiveness of the electrodes are related to the number of coating layers and the annealing temperature. Using ligand coordinated titanium-oxo-clusters as the molecular precursors of TiO2 anatase films is found to be effective due to their high solubility, appropriate stability in solution and hence the easy controllability.