Towards understanding the NTB phase: a combined experimental, computational and spectroscopic study

Abstract

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 (N_TB) 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 N_TB 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 N_TB 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 N_TB phase.