Theoretical Investigation of Adsorption, Dynamics, Self-Aggregation, and Spectroscopic Properties of the D102 Indoline Dye on an Anatase (101) Substrate

A coherent account of adsorption modes, dynamics, self aggregation, and spectroscopic properties of an indoline organic dye adsorbed on TiO2 anatase (101) substrates is reported. The study is performed by combining reactive molecular dynamics (reaxFF) simulations with time-dependent density functional theory calculations, and the reliability of the results is assessed through comparison with theoretical and experimental data available in the literature. The use of a theoretical multilevel approach has proven to be crucial to gain a deep understanding, at an atomistic level, of the morphology and electronic properties of dye-sensitized heterogeneous interfaces. A realistic description of the functionalized anatase (101) interface, where a variety of binding modes are present, has been achieved by means of extensive molecular dynamics simulations of the adsorption of dye clusters made of different molecular units on medium/large size TiO2 anatase slabs. Our results disclose that the main driving forces toward formation of ordered surface aggregates are pi stacking and T-shaped interactions between the aromatic rings of the donor moiety of the molecules, as well as the tendency to maximize the anchoring points with the surface. The dye aggregates were found to be organized in domains, characterized by a different orientation of the packing units, and, in the high coverage limit, presenting a certain degree of short-to-medium range order.