Ferroelectric Liquid-Crystalline Binary Mixtures Based on Achiral and Chiral Trifluoromethylphenylterthiophenes

Abstract

This paper presents a new family of ferroelectric smectic liquid-crystalline binary mixtures composed of achiral and chiral trifluoromethylphenylterthiophenes. The chiral symmetry breaking of the ferroelectric smectic phases can lead to chiral photovoltaic (CPV) effects, as a type of ferroelectric photovoltaic (FePV) effect, which is caused by the internal electric field originating from the spontaneous polarization. These ferroelectric properties were examined using the Sawyer–Tower method, and the CPV effect was confirmed by measuring the steady-state photocurrent response under zero bias. We found that the remnant polarization and photocurrent density in the polarized ferroelectric phases increased nonlinearly with the increase in the content of the chiral component in the mixture. Moreover, the hole mobility evaluated by time-of-flight measurements was kept constant by varying the composition. More than 40 mol % of the chiral component was required to form the polar structure, inducing the CPV effect. Binary mixture systems are advantageous for not only optimizing liquid crystal structures and temperature ranges but also facilitating the design of materials exhibiting CPV effects.

Pronounced Chirality Effect on the Ferroelectricity of Hydrogen-Bonded Supramolecular Assemblies of Ambipolar Chromophoric Systems

“…It is noteworthy that helical fibers were noticed for the chiral supramolecular assembly, while no such helical bias was seen for the supramolecular assembly of the achiral system. The decisive role of homochirality on ferroelectricity in molecular self-assembled systems, as evident from the present study, is a significant new knowledge that should be useful not only for designing new ferroelectric materials but also for organic piezoelectric materials, which are promising for self-powered electronics for mechanical-to-electrical energy conversion. − While it may not be universally true that chirality is essential for realizing symmetry breaking in all organic molecular systems, our results strongly indicate that homochirality could greatly enhance the possibility of realizing a much-improved performance in ferroelectric or piezoelectric organic materials. Considering the vast possibilities of molecular engineering in organic supramolecular systems for fine-tuning the molecular structure and macroscopic organization, these results may provide an important guideline for the further development of organic FE materials, which are of emerging interest for exploring lightweight, easily processed, and environment-friendly electronics.…”

Chiral Liquid Crystalline Electronic Systems

“…This bulk photovoltaic effect was also observed in binary systems consisting of a chiral and achiral FLCs [79]. The chirality induced by a small amount of chiral dopant can break the centrosymmetry of the LC electronic system, resulting in the photovoltaic effect in the ferroelectric LC phase [80]. As shown in Figure 14b, the photovoltaic effect was induced by doping of chiral compound 26 to achiral LC 25.…”

Sum-Frequency Generation and Scanning Electron Microscope Studies on Second-Harmonic Generation Active Structures of Sacran Aggregates

“…The third candidate is a possible ferroelectric liquid crystal phase of sacran molecules. Sacran has abundant chiral units giving possible structures to form a ferroelectric liquid crystal (FLC) [34,35]. Permanent electric dipoles of the sacran chain can occur if the chain takes a spiral structure by the effect of the alternate alignment between non-chiral and chiral molecules.…”