Electronic structures of quinizarin complexed with TiO2 clusters

Electronic structure calculations using the semiempirical method PM3 were performed on quinizarin complexed with TiO2 clusters. At first, electronic structure calculations of quinizarin complexed with small TiO2 clusters were performed to check a reliability of the parameters. The calculated transition energies were correlated to the observed absorption spectra. Then, TiO2 cluster was expanded into rutile type cluster which contained 11 Ti4+ ions. The LUMO of quinizarin complexed with the cluster was greater than the CB of the matrix. The replacements of Ti4+ ions by Si4+ ions changed the densitiy of states of the matrix. The increase of Si4+ sites shifted the CB to larger energy, and a change of relative energy level of the CB to the LUMO of the dye was observed. This result was consistent with a consideration from the TiO2 content dependence of the fluorescence lifetimes of quinizarin. (C) 2000 Kluwer Academic Publishers.