Computational Modeling of Stark Effects in Organic Dye-Sensitized TiO2 Heterointerfaces

We report a computational modeling study, based on DFT and time-dependent DFT techniques, to investigate the origin and the effect of local electric fields on the optical properties of organic dye-sensitized heterointerfaces, examining the case of the indoline D149 sensitizer on TiO2. On the one hand, we give precise information about the anchoring mode of D149 and its orientation with respect to the TiO2 surface, and on the other hand, we provide the computational framework model to interpret the Stark shifts experimentally observed by PIA spectroscopy. Our results show that the presence of oxidized dye molecules induces major spectral changes on the adjacent neutral dyes, which, along with the simulated effect of injected charge into TiO2, provide Stark shifts nicely reproducing the experimental observations.