Fine-tuning the effect of π-π interactions on the stability of the N TB phase.

The synthesis and liquid-crystalline properties are reported for novel bent-shaped dimers in which a naphthyl group has been incorporated into the mesogenic cores. In addition to the nematic and twist-bend nematic phase, a new liquid-crystalline phase was observed. The combined experimental and computational study demonstrated how the interplay between the molecular geometry and pi-pi interactions affects the thermal stability of the twist-bend nematic and nematic phases. Correlation between mesomorphic properties and molecular geometry revealed that a greater conformational diversity leads to a broader distribution of bend-angles and destabilization of the N-TB phase. Qualitative correlation between the thermal behaviour and electronic structure of the molecules of a similar geometry suggested that the transition temperatures of both nematic phases depend on the relative contribution of dispersion and electrostatic energies which determines the strength of the pi-pi interactions. These results provide an insight into how subtle changes in chemical structure can be exploited to tune the intermolecular interactions and influence the thermal stability of the liquid crystalline phase.