Ultrastable liquid crystalline blue phase from molecular synergistic self-assembly

Fabricating functional materials via molecular self-assembly is a promising approach, and precisely controlling the molecular building blocks of nanostructures in the self-assembly process is an essential and challenging task. Blue phase liquid crystals are fascinating self-assembled three-dimensional nanomaterials because of their potential information displays and tuneable photonic applications. However, one of the main obstacles to their applications is their narrow temperature range of a few degrees centigrade, although many prior studies have broadened it to tens via molecular design. In this work, a series of tailored uniaxial rodlike mesogens disfavouring the formation of blue phases are introduced into a blue phase system comprising biaxial dimeric mesogens, a blue phase is observed continuously over a temperature range of 280 °C, and the range remains over 132.0 °C after excluding the frozen glassy state. The findings show that the molecular synergistic self-assembly behavior of biaxial and uniaxial mesogens may play a crucial role in achieving the ultrastable three-dimensional nanostructure of blue phases.

Blue phases are spatially ordered yet fragile liquid crystalline structures, bearing applications in optoelectronics and photonics. Hu et al. show that self-assembly within a mixture of different mesogens may significantly broaden the temperature range over which they are stable.

Nature-Inspired Emerging Chiral Liquid Crystal Nanostructures: From Molecular Self-Assembly to DNA Mesophase and Nanocolloids

Liquid crystals (LCs) are omnipresent in living matter, whose chirality is an elegant and distinct feature in certain plant tissues, the cuticles of crabs, beetles, arthropods, and beyond. Taking inspiration from nature, researchers have recently devoted extensive efforts toward developing chiral liquid crystalline materials with self-organized nanostructures and exploring their potential applications in diverse fields ranging from dynamic photonics to energy and safety issues. In this review, an account on the state of the art of emerging chiral liquid crystalline nanostructured materials and their technological applications is provided. First, an overview on the significance of chiral liquid crystalline architectures in various living systems is given. Then, the recent significant progress in different chiral liquid crystalline systems including thermotropic LCs (cholesteric LCs, cubic blue phases, achiral bent-core LCs, etc.) and lyotropic LCs (DNA LCs, nanocellulose LCs, and graphene oxide LCs) is showcased. The review concludes with a perspective on the future scope, opportunities, and challenges in these truly advanced functional soft materials and their promising applications.

The effects of molecular structure and functional group of a rodlike Schiff base mesogen on blue phase stabilization in a chiral system

A wider blue phase (BP) range can be induced easily when two difluoro substituted and racemic rodlike Schiff base mesogens are doped with the appropriate concentration of chiral dopants S811 or ISO(6OBA)2.

Enhanced Low-temperature Electro-optical Kerr Effect of Stable Cubic Soft Superstructure Enabled by Fluorinated Polymer Stabilization

An enhanced electro-optical Kerr effect of the stable self-organized cubic blue phase liquid crystal superstructure at a relatively low temperature down to -50 °C was achieved through a judiciously designed fluorinated polymer stabilization. The fluorinated sample exhibited not only a rather stable cubic structure, but the promoted electro-optical performances of low driving voltage, weak hysteresis and high contrast ratio at such a low-temperature, which were much distinct from the common non-fluorinated polymer stabilized blue phase liquid crystal without conspicuous low-temperature Kerr response behaviours. Kerr constant, which reflects the obviousness of Kerr effect, of the fluorinated sample at -50 °C indicated a spectacular enhancement of two orders of magnitude in contrast to the commonly material, thereby corroborating the high efficiency of polymer fluorination in enhancing low-temperature Kerr effect. Such an enhancement of Kerr effect was probably resulted from the decreasing of interfacial anchoring between liquid crystal and fluorinated polymer network. The fluorinated polymer stabilization not only ensures the stability of self-organized cubic structure of blue phase, but overcomes the challenge and bottleneck problem of low-temperature inapplicability of common blue phase liquid crystal and paves a brilliant and broad way for relevant materials to abundant perspective applications at low temperature.

Wide blue phase range observed in simple binary mixture systems containing rodlike racemic biphenyl mesogens with 2-octyloxy tails

The widest temperature range of BP (∼34 K) can be induced by adding only 10 wt% chiral dopant ISO(6OBA)2 with high HTP into the rodlike racemic biphenyl compound C6OBiPhI-H.

Hydrogen-bonded bent-core blue phase liquid crystal complexes containing various molar ratios of proton acceptors and donors

The molar ratio, alkyl chain length, lateral fluoro-substitution and the chiral center of H-bonded bent-core supramolecules would affect the BP ranges of BPLC complexes. H-bonded bent-core complex PIIIC9/AIIF* (3/7 mol mol⁻¹) displayed the widest BPI range of ΔT_BPI = 12 °C.

Blue phase liquid crystal: strategies for phase stabilization and device development

The blue phase liquid crystal (BPLC) is a highly ordered liquid crystal (LC) phase found very close to the LC-isotropic transition. The BPLC has demonstrated potential in next-generation display and photonic technology due to its exceptional properties such as sub-millisecond response time and wide viewing angle. However, BPLC is stable in a very small temperature range (0.5-1 °C) and its driving voltage is very high (∼100 V). To overcome these challenges recent research has focused on solutions which incorporate polymers or nanoparticles into the blue phase to widen the temperature range from around few °C to potentially more than 60 °C. In order to reduce the driving voltage, strategies have been attempted by modifying the device structure by introducing protrusion or corrugated electrodes and vertical field switching mechanism has been proposed. In this paper the effectiveness of the proposed solution will be discussed, in order to assess the potential of BPLC in display technology and beyond.

Hydrogen-bonded effects on supramolecular blue phase liquid crystal dimeric complexes

The number/position of chiral centers and the molar ratios of H-donors/H-acceptors affect the blue phase ranges of asymmetric H-bonded complexes.

Stabilization and optical switching of liquid crystal blue phase doped with azobenzene-based bent-shaped hydrogen-bonded assemblies

Stabilization and phototuning of the reflection color of BP I have been demonstrated in a BP-LCs by employing a new kind of bent-shaped H-bonded assemblies with azobenzene group.

Novel asymmetrical single- and double-chiral liquid crystal diads with wide blue phase ranges

Novel asymmetrical single- and double-chiral liquid crystal diads are reported, where diad III-D exhibited the widest range of BPI about 31 °C. Large biaxiality and dipole moment of the bent molecule are useful to extend the BP temperature range.

Broad ranges and fast responses of single-component blue-phase liquid crystals containing banana-shaped 1,3,4-oxadiazole cores

In this study, we synthesized two novel 1,3,4-oxadiazole-based bent-core liquid crystals (OXD7*, OXD5B7F*) containing a chiral tail that display broad ranges of the blue phase III (34 and 7 K, respectively); we characterized them using polarized optical microscopy, differential scanning calorimetry, and circular dichroism. The electro-optical responses of both of these liquid crystals are much faster than those of previously reported single-component blue-phase liquid crystals. To optimize its electro-optical performance, we mixed OXD7* (the blue-phase range of which is broader than that of OXD5B7F*) with its analogue OXD6 (at weight ratios of 6:4 and 4:6). We also performed molecular modeling of single-component BPLCs (OXD7* and OXD5B7F*) to analyze the possible parameters affecting their blue phase ranges.

Liquid-crystalline blue phase II system comprising a bent-core molecule with a wide stable temperature range

A thermodynamically stable blue phase II (BPII) has been prepared, and its electrooptical (EO) performance has been evaluated in a host system of a conventional rodlike nematogen mixed with a bent-core molecule. For the mixed system presented, the widest temperature range of BPII stability, during cooling/heating, was >6 °C. This range is much wider than those of conventional nematogens blended with chiral dopants. EO observations show that the BPII produced exhibited stable EO performance based on the EO Kerr effect. The temperature dependence of the Kerr effect was found to be in approximate agreement with the Landau-de Gennes theory. Furthermore, this material demonstrated very fast, sub-millisecond-scale, response times, thus showing potential for use in high-speed EO devices.

Nanoconfinement-induced structures in chiral liquid crystals

We employ Monte Carlo simulations in a specialized isothermal-isobaric and in the grand canonical ensemble to study structure formation in chiral liquid crystals as a function of molecular chirality. Our model potential consists of a simple Lennard-Jones potential, where the attractive contribution has been modified to represent the orientation dependence of the interaction between a pair of chiral liquid-crystal molecules. The liquid crystal is confined between a pair of planar and atomically smooth substrates onto which molecules are anchored in a hybrid fashion. Hybrid anchoring allows for the formation of helical structures in the direction perpendicular to the substrate plane without exposing the helix to spurious strains. At low chirality, we observe a cholesteric phase, which is transformed into a blue phase at higher chirality. More specifically, by studying the unit cell and the spatial arrangement of disclination lines, this blue phase can be established as blue phase II. If the distance between the confining substrates and molecular chirality are chosen properly, we see a third structure, which may be thought of as a hybrid, exhibiting mixed features of a cholesteric and a blue phase.

Compensation of blue phase I by blue phase II in optoeletronic device

Compensation effect of blue phase I (BP I) with blue phase II (BP II) liquid crystal was demonstrated. BP I and BP II were co-exist in the optoeletronic device by polymer stabilization. Consequently, disadvantages of BP I and BP II were greatly improved by compensation effect and resulted in high contrast ratio, low hysteresis and fast falling time. Mechanism of compensation effect was explained by relaxation ability of lattice structure under electrical field and compensation structure was well confirmed by Bragg's reflectance spectrum and Commission International de l'Éclairage chromaticity diagram.

Synthesis and conformation of substituted chiral binaphthyl-azobenzene cyclic dyads with chiroptical switching capabilities

Optically active binaphthyl-azobenezene cyclic dyads were synthesized to develop a photochromic switching molecule. Azobenezene moieties were cis-trans isomerized by photoirradiation. As a reflection of the structural change, the specific optical rotation and circular dichroism underwent significant shifts. Under certain conditions, the positive-negative and zero-positive (or zero-negative) signals were reversed. Optical rotation may potentially be applied in noise-cancelling nondestructive photoswiches. The conformations were studied by experimental and theoretical methods. The results revealed that the helical chirality, (P) or (M), of the cis-azobenzene moiety was induced by intramolecular axial chirality. The twist direction depended on the axial chirality as well as the azobenzene linkage position to the binaphthyls, but was independent of the identity of substituted groups. 2,2’-Linked-(R)-binaphthyl was found to induce cis-(P)-azobenzene, whereas symmetrically 7,7’-linked-(R)-binaphthyl was found to induce cis-(M)-azobenzene.

Nanoparticle-induced widening of the temperature range of liquid-crystalline blue phases

Liquid-crystalline blue phases exhibit exceptional properties for applications in the display and sensor industry. However, in single component systems, they are stable only for very narrow temperature range between the isotropic and the chiral nematic phase, a feature that severely hinders their applicability. Systematic high-resolution calorimetric studies reveal that blue phase III is effectively stabilized in a wide temperature range by mixing surface-functionalized nanoparticles with chiral liquid crystals. This effect is present for two liquid crystals, yielding a robust method to stabilize blue phases, especially blue phase III. Theoretical arguments show that the aggregation of nanoparticles at disclination lines is responsible for the observed effects.