Towards understanding the NTB phase: a combined experimental, computational and spectroscopic study†
Today liquid-crystalline materials are most widely exploited for flat-panel displays, and yet their ability to self-organize into periodically ordered nanostructures gives rise to a broad variety of additional applications. The recently discovered low-temperature nematic phase (NTB) with unusual characteristics generated considerable attention within the scientific community: despite the fact that the molecules from which the phase is composed are not chiral, the helicoidal structure of the phase is strongly implicated. Here we present a combined experimental, computational and spectroscopic study of the structural aspects influencing the formation of the NTB phase as well as the possible molecular organization within the phase. In an extensive DFT study, the structure–property prerequisite was traced to a “bent-propeller” shape of the molecule. Computational analysis of two possible types of molecular packing suggests that the syn-arrangement of dimeric molecules is energetically more favorable than the anti-arrangement. The NOESY investigation in the isotropic melt just prior to the Iso–N transition shows the presence of intermolecular interactions that can be attributed to the syn-parallel orientation of the mesogens. The synergy of experimental, computational and NMR studies provides a new insight into possible molecular organization within the NTB phase, supporting the hierarchical model in which self-assembly of dimeric molecules with syn-parallel orientation formed in the isotropic melt represents the nucleus for its complex helical superstructures in the NTB phase.