The role of intermolecular interactions in stabilizing the structure of the nematic twist-bend phase

The understanding of the relationship between molecular structure and the formation of the nematic twist-bend phase is still at an early stage of development. This is mainly related to molecular geometry, while the correlation between the nematic twist-bend phase and the electronic structure is ambiguous. To explore the electronic effect on properties and stabilization of the nematic twist-bend phase we investigated 2',3'-difluoro-4,4''-dipentyl-p-terphenyl dimers (DTC5Cn). We used polarized fourier transform infrared spectroscopy, which can, at least in principle, provide information about the ordering in the twist-bend phase. All dimers show a significant drop in the average value of the transition dipole moment for parallel dipoles at the transition from the nematic to the twist-bend phase, and an increase for perpendicular dipoles, despite remaining unchanged for the monomer. Density functional theory calculations were used to determine the geometric and electronic properties of the hydrogen bonded complexes. We have provided experimental and theoretical evidence of stabilization of the nematic twist-bend phase by arrays of multiple hydrogen bonds (XF⋯HX, X-benzene ring).