Ferroelectrically Switching Helical Columnar Assembly Comprising Cisoid Conformers of a 1,2,3-Triazole-based Liquid Crystal.

The 1,2,3-triazole molecule, which is a product of click chemistry, possesses a high dipole moment and can be a useful polar motif for ferroelectric columnar liquid crystal (LC) materials-though it has not been used to date. Herein, we report the helical assembly and ferroelectric switching properties of a columnar liquid crystal comprising a naphthalene core and 1,2,3-triazolyl linkages. The molecule assembles into a double-stranded helical columnar LC structure (Colhel ). The X-ray simulations of cisoid and transoid columnar models suggest that the helical assembly comprises cisoid conformers with a non-zero dipole moment. The helical columns in the Colhel phase are aligned homeotropically under an electric field. The ferroelectric switching of the axial polarization can be observed in the temperature range of 105-115 °C in the Colhel phase, wherein the triazolyl hydrogen bonding along the column axis is weakened. The ferroelectric switching event is attributed to the rotation of the polar triazolyl units in response to the electric field.

The Role of the 1,2,3-Triazolyl Heterocycle in the Helical Columnar Assembly and Electric Field Response.

Here, we have proven the role of the 1,2,3-triazolyl group in the helical assembly and electric field (E-field) response upon comparing liquid crystal analogs 1 and 2 based on 1,2,3-triazolyl and 1,3,4-oxadiazolyl linkers, respectively. An ordered helical column was only observed in 1, driven by the hydrogen-bonding interactions between the adjacent triazolyl nitrogen and hydrogen atoms. X-ray diffraction and energy simulations indicate that the helical column is a 112 helix and the helical axis does not coincide with the center of the molecular long axis. The key for the formation of the helical column is the tilted conformation of 1 originating from the steric repulsion between the triazolyl C-H and C-H of the aromatic core. Analysis of the dynamics in the simple hexagonal columnar phase revealed that the in-plane rotational motion of the triazolyl linker (1) is allowed, while the oxadiazolyl linker of 2 has limited conformational flexibility. A uniform alignment under an E-field only occurs in 1, demonstrating the requirement for conformational flexibility in the polar linker. This alignment enhances the electric conductance of 1 by approximately two-fold.