Electronic structures of quinizarin complexed with TiO2 clusters

Electronic structure calculations using the semiempirical method PM3 were p erformed on quinizarin complexed with TiO2 clusters. At first, electronic s tructure calculations of quinizarin complexed with small TiO2 clusters were performed to check a reliability of the parameters. The calculated transit ion 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 dens itiy 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 fr om the TiO2 content dependence of the fluorescence lifetimes of quinizarin. (C) 2000 Kluwer Academic Publishers.