Titanium–Oxo Cluster with 9‑Anthracenecarboxylate Antennae: A Fluorescent and Photocurrent Transfer Material

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(OiPr)6(9-AC)6] (1) and [Ti6O4(OiPr)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.