Range-Separated Hybrid Density Functional Study of Organic Dye Sensitizers on Anatase TiO2 Nanowires

The adsorption of organic molecules coumarin and the donor-p-acceptor type tetrahydroquinoline (C2-1) on anatase (101) and (001) nanowires has been investigated using screened Coulomb hybrid density functional theory calculations. Simple coumarin core forms a single bond with the TiO2. C2-1 exhibits a bidentate mode giving rise to much stronger adsorption energies on the nanowire surface. Nonlinear solvation effects on the binding characteristics of the dye chromophores on the nanowire facets have also been examined. These two dye sensitizers show different electronic charge distributions for the highest occupied and the lowest unoccupied molecular states. We studied the electronic structures in terms of the positions of the band edges and adsorbate-related gap states and their effect on the absorption spectra of the dyenanowire combined systems. These findings were interpreted and discussed from the viewpoint of better light harvesting and charge separation as well as in relation to more efficient charge carrier injection into the semiconductor nanowire