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.