Structure and dynamics of TiO2-anchored D205 dye in ionic liquids and acetonitrile
Résumé
Molecular dynamics computer simulations of the solid-liquid interface of TiO2 and D205 dye (anchored or free) and solvent, such as ionic liquids (1-butyl-3-methylimidazolium with hexafluorophosphate (BmimPF6) and trifluoromethanesulfonate (BmimTFO) anions) or acetonitrile (ACN) are performed in the canonical (NVT) ensemble. For the solvent and TiO2, we used the force fields availabile in the literature or developed by us, while to described the TiO2 and D205 interactions, quantum-chemical calculations were carried out on a small size cluster of TiO2 where the D205 dye was anchored. The simulations were carried systematically in the absence or presence of the D205 dye. In the latter case, we consider the situation where the dye is covalently anchored or free at the interface. The solvent molecules, forming the first layers at the TiO2 interface, have been identified by analyzing the mass density distribution and radial distribution functions. The results show that the solvent molecules are structured in successive layers, the density of which decreases to reach that of the macroscopic one at a long distance normal to the TiO2 interface. These findings show also that the F and O atoms of the anions and the N atom of acetonitrile are at a close distance from the Ti or O atoms of the TiO2 surface, indicating a competition of the solvent and the dye to interact with these atoms. Furthermore, the time traces of the z-axis position of certain atoms of the anchored D205 dye did not show any substantial change suggesting the conformation change is not occurring in the time scale of 50 ns.