Organic chiral nano- and microfilaments: types, formation, and template applications

Controlling nano- and microfilament morphology by strategically placing chiral centers in the side chains of bent-core molecules

Self-assembled lamellar nano- and microfilaments formed by select types of bent-core molecules are prime examples of the interplay between molecular conformation and morphological chirality. Here, we demonstrate how the strategic placement of chiral centers at C-1 and/or C-3 in the terminal alkyloxy side chains, largely based on a priori calculations of molecular conformation, leads to the predictable formation of increasingly complex nano- and microfilament morphologies. Adding to the previously described diversity of twisted and writhed filament types, we here demonstrate and explain the formation and coexistence of flat nanoribbons, nanocylinders, or nano- as well as microfilaments where the morphology spontaneously changes along the filament long axis. For some these more exotic types of filament morphology, helical multilayer filaments suddenly unwind to form flat nanoribbons that also twist again under preservation (not perversion) of the helical twist sense. Moreover, the morphologies formed by this series of molecules now allows us to demonstrate the complete transformation from flat multilayer ribbons over microfilaments and helical-wrapped nanocylinders to helical nanofilaments depending on the number and position of chiral centers in the aliphatic side chains.

Ionic Bent-Core Pillar[n]arenes: From Liquid Crystals to Nanoaggregates and Functional Applications

Herein, we report the first examples of supramolecular systems from bent-core-based pillar[n]arenes through ionic bonds. These ionic materials have been prepared by the interaction of an amino-ended pillar[5]arene (P5N10) and three different carboxylic acids, including bent-core moieties. The bent-core units are based on ester, biphenyl, and azobenzene structures bearing two different flexible spacers between the carboxyl group and the central bent-core aromatic units. The ionic pairs segregate the molecular blocks, leading to columnar liquid crystal organizations. These ionic supramolecular compounds exhibit interesting results as proton-conductive materials. Furthermore, the introduction of azobenzene units in the bent-core structure has provided a photoresponse to the proton conduction materials. Interestingly, the amphiphilic character generated by the ionic pairs and the hydrophobic bent-core structures allows their molecular self-assembly in water solution, resulting in aggregates of appealing morphologies. The structural modifications of the bent-core units (i.e., connecting bonds at the lateral structure and spacer lengths) provide an attractive analysis on the relationship between the chemical structure and the morphology of the aggregates (fibers, chiral ribbons, nanotubes...). Additionally, the self-assembly process and evolution of the aggregates from fibers to nanotubes have been studied with several techniques.

Polymerization strategy for cellulose nanocrystals-based photonic crystal films with water resisting property

Cellulose nanocrystals (CNCs) can form a liquid crystal film with a chiral nematic structure by evaporative-induced self-assembly (EISA). It has attracted much attention as a new class of photonic liquid crystal material because of its intrinsic, unique structural characteristics, and excellent optical properties. However, the CNCs-based photonic crystal films are generally prepared via the physical crosslinking strategy, which present water sensitivity. Here, we developed CNCs-g-PAM photonic crystal film by combining free radical polymerization and EISA. FT-IR, SEM, POM, XRD, TG-DTG, and UV-Vis techniques were employed to characterize the physicochemical properties and microstructure of the as-prepared films. The CNCs-g-PAM films showed a better thermo-stability than CNCs-based film. Also, the mechanical properties were significantly improved, viz., the elongation at break was 9.4 %, and tensile strength reached 18.5 Mpa, which was a much better enhancement than CNCs-based film. More importantly, the CNCs-g-PAM films can resist water dissolution for more than 24 h, which was impossible for the CNCs-based film. The present study provided a promising strategy to prepare CNCs-based photonic crystal film with high flexibility, water resistance, and optical properties for applications such as decoration, light management, and anti-counterfeiting.

Macroscopic Biaxial Order in Multilayer Films of Bent-Core Liquid Crystals Deposited by Combined Langmuir-Blodgett/Langmuir-Schaefer Technique

Bent-core liquid crystals, a class of mesogenic compounds with non-linear molecular structures, are well known for their unconventional mesophases, characterized by complex molecular (and supramolecular) ordering and often featuring biaxial and polar properties. In the nematic phase, their unique behavior is manifested in the formation of nano-sized biaxial clusters of layered molecules (cybotactic groups). While this prompted their consideration in the quest for nematic biaxiality, experimental evidence indicates that the cybotactic order is only short-ranged and that the nematic phase is macroscopically uniaxial. By combining atomic force microscopy, neutron reflectivity and wide-angle grazing-incidence X-ray scattering, here, we demonstrate that multilayer films of a bent-core nematic, deposited on silicon by a combined Langmuir-Blodgett and Langmuir-Schaefer approach, exhibit macroscopic in-plane ordering, with the long molecular axis tilted with respect to the sample surface and the short molecular axis (i.e., the apex bisector) aligned along the film compression direction. We thus propose the use of Langmuir films as an effective way to study and control the complex anchoring properties of bent-core liquid crystals.

Research Progress of Electrically Driven Multi-Stable Cholesteric Liquid Crystals

Electrically driven multi-stable cholesteric liquid crystals can be used to adjust the transmittance of incident light. Compared with the traditional liquid crystal optical devices, the multi-stable devices only apply an electric field during switching and do not require a continuous electric field to maintain the various optical states of the device. Therefore, the multi-stable devices have low energy consumption and have become a research focus for researchers. However, the multi-stable devices still have shortcomings before practical application, such as contrast, switching time, and mechanical strength. In this article, the latest research progress on electrically driven multi-stable cholesteric liquid crystals is reviewed, including electrically driven multi-stable modes, performance optimization, and applications. Finally, the challenges and opportunities of electrically driven multi-stable cholesteric liquid crystals are discussed in anticipation of contributing to the development of multi-stable liquid crystal devices.