Ab Initio Molecular Dynamics Studies of the Effect of Solvation by Room-Temperature Ionic Liquids on the Vibrational Properties of a N719-Chromophore/Titania Interface

The accurate ab initio modeling of prototypical and well-representative photoactive interfaces for candidate dye-sensitized solar cells (DSCs) is a perennial problem in physical chemistry. To this end, the use of ab initio density functional theory-based molecular dynamics (AIMD) has been studied here to investigate the effect the choice of functional has on a system mimicking the essential workings of a DSC: the energetic properties of a [bmim]+[NTf2]- room-temperature ionic liquid (RTIL) solvating an N719-sensitizing dye adsorbed onto an anatase-titania (101) surface were scrutinized. In so doing, we glean important insights into how using an RTIL as electrolytic hole acceptor alters and modulates the dynamical properties of the widely used N719 dye. A fully crossed study has been carried out comparing the Becke-Lee-Yang-Parr (BLYP) and Perdew-Burke-Ernzerhof (PBE) functionals, both unsolvated and solvated by the RTIL, both with and without Grimme D3 dispersion corrections. Also, vibrational spectra for the photoactive interface in the DSC configuration were calculated by means of Fourier-transforming atomic mass-weighted velocity autocorrelation functions. The ab initio vibrational spectra were compared to high-quality experimental data and against each other; the effects of various methodological choices on the vibrational spectra were also studied, with PBE generally performing best in producing spectra, which matched the experimental frequency modes typically expected.