Short bent-core molecules: X-ray, polarization, dielectricity, texture and electro-optics investigations

Nanostructure of Unconventional Liquid Crystals Investigated by Synchrotron Radiation

The macroscopic properties of novel liquid crystal (LC) systems-LCs with unconventional molecular structure as well as conventional LCs in unconventional geometries-directly descend from their mesoscopic structural organization. While X-ray diffraction (XRD) is an obvious choice to investigate their nanoscale structure, conventional diffractometry is often hampered by experimental difficulties: the low scattering power and short-range positional order of the materials, resulting in weak and diffuse diffraction features; the need to perform measurements in challenging conditions, e.g., under magnetic and/or electric fields, on thin films, or at high temperatures; and the necessity to probe micron-sized volumes to tell the local structural properties from their macroscopic average. Synchrotron XRD allows these problems to be circumvented thanks to the superior diffraction capabilities (brilliance, q-range, energy and space resolution) and advanced sample environment available at synchrotron beamlines. Here, we highlight the potentiality of synchrotron XRD in the field of LCs by reviewing a selection of experiments on three unconventional LC systems: the potentially biaxial and polar nematic phase of bent-core mesogens; the very high-temperature nematic phase of all-aromatic LCs; and polymer-dispersed liquid crystals. In all these cases, synchrotron XRD unveils subtle nanostructural features that are reflected into macroscopic properties of great interest from both fundamental and technological points of view.

Dielectric Relaxation and Beyond Limiting Behavior of Alternating-Current Conductivity in a Supermolecular Ferroelectric

A cyclen-based hybrid supermolecule crystal, [(FeCl₂ )(cyclen)]Cl (1), where cyclen=1,4,7,10-tetraazacyclododecane, was prepared using a liquid-liquid diffusion approach. The variable crystal structures exhibit that compound 1 belongs to an orthorhombic crystal system, Pna2₁ space group (point group C_2V ) in the temperature range of 150-400 K. This hybrid supermolecule shows a dielectric relaxation behavior around room temperature, and the ferroelectric nature of 1 has been directly verified by hysteresis measurements. In addition, the AC (alternating current) conductivity study reveals that the 1 displays a beyond limiting behavior. These interesting findings are for the first time reported in the field of supermolecular ferroelectrics. This study may open a new way to construct supermolecular ferroelectrics and give insights into their conductor behavior.