Chiral Side Groups Trigger Second Harmonic Generation Activity in 3D Octupolar Bipyrimidine‐Based Organic Liquid Crystals

The design of efficient noncentrosymmetric materials remains the ultimate goal in the field of organic second‐order nonlinear optics. Unlike inorganic crystals currently used in second‐order nonlinear optical applications, organic materials are an attractive alternative owing to their fast electro‐optical response and processability, but their alignment into noncentrosymmetric film remains challenging. Here, symmetry breaking by judicious functionalization of 3D organic octupoles allows the emergence of multifunctional liquid crystalline chromophores which can easily be processed into large, flexible, thin, and self‐oriented films with second harmonic generation responses competitive to the prototypical inorganic KH₂PO₄ crystals. The liquid‐crystalline nature of these chiral organic films also permits the modulation of the nonlinear optical properties owing to the sensitivity of the supramolecular organization to temperature, leading to the development of tunable macroscopic materials.     

Liquid‐Crystalline Ordering as a Concept in Materials Science: From Semiconductors to Stimuli‐Responsive Devices

While the unique optical properties of liquid crystals (LCs) are already well exploited for flat‐panel displays, their intrinsic ability to self‐organize into ordered mesophases, which are intermediate states between crystal and liquid, gives rise to a broad variety of additional applications. The high degree of molecular order, the possibility for large scale orientation, and the structural motif of the aromatic subunits recommend liquid‐crystalline materials as organic semiconductors, which are solvent‐processable and can easily be deposited on a substrate. The anisotropy of liquid crystals can further cause a stimuli‐responsive macroscopic shape change of cross‐linked polymer networks, which act as reversibly contracting artificial muscles. After illustrating the concept of liquid‐crystalline order in this Review, emphasis will be placed on synthetic strategies for novel classes of LC materials, and the design and fabrication of active devices.     

Liquid crystal mediated interactions between nanoparticles in a nematic phase

A continuum theory is used to study the interactions between nanoparticles suspended in nematic liquid crystals. The free energy functional that describes the system is minimized using an Euler-Lagrange approach and an unsymmetric radial basis function method. It is shown that nanoparticle liquid-crystal mediated interactions can be controlled over a large range of magnitudes through changes of the anchoring energy and the particle diameter. The results presented in this work serve to reconcile past discrepancies between theoretical predictions and experimental observations, and suggest intriguing possibilities for directed nanoparticle self-assembly in liquid crystalline media.     

柔性高分子/小分子液晶混合物的自洽场理论

发展了柔性高分子/小分子液晶混合物连续自洽场理论，将小分子液晶模型化 为取向与位置无关的单体分子，小分子液晶间存在各向异性的Maier-Saupe相互作 用，该理论可还原成高分子和各向同性小分子组成的Flory-Huggins溶液理论和纯 液晶的Maier-Squpe液晶理论，通过数值解自洽场方程组，还将理论用于研究柔性 高分子/小分子液晶混合物相分离开界面性质，得到的结果与用Helfand格子界面理 论和MOnte Carlo模拟的结果一致。     

Reformulation of Maxwell's equations to incorporate near-solute solvent structure

Maxwell's equations, which treat electromagnetic interactions between macroscopic charged objects in materials, have explained many phenomena and contributed to many applications in our lives. Derived in 1861 when no methods were available to determine the atomic structure of macromolecules, Maxwell's equations assume the solvent to be a structureless continuum. However, near-solute solvent molecules are highly structured, unlike far-solute bulk solvent molecules. Current methods cannot treat both the near-solute solvent structure and time-dependent electromagnetic interactions in a macroscopic system. Here, we derive "microscopic" electrodynamics equations that can treat macroscopic time-dependent electromagnetic field problems like Maxwell's equations and reproduce the solvent molecular and dipole density distributions observed in molecular dynamics simulations. These equations greatly reduce computational expense by not having to include explicit solvent molecules, yet they treat the solvent electrostatic and van der Waals effects more accurately than continuum models. They provide a foundation to study electromagnetic interactions between molecules in a macroscopic system that are ubiquitous in biology, bioelectromagnetism, and nanotechnology. The general strategy presented herein to incorporate the near-solute solvent structure would enable studies on how complex cellular protein-ligand interactions are affected by electromagnetic radiation, which could help to prevent harmful electromagnetic spectra or find potential therapeutic applications.     

非传统型液晶分子设计与工程研究进展

从液晶基元连接方式、液晶分子拓扑结构以及凝聚态自组织方式等方面扼要介绍和评述了非传统型液晶分子设计与工程研究进展,并重点介绍了可望引起液晶显示技术革命的双轴向列相香蕉形液晶研究的突破性工作,展望了非传统型液晶分子设计和复杂自组织超分子液晶领域今后的发展方向。     

Cation-Induced Macroscopic Ordering of Non-Mesomorphic Modules—A New Application for Metallohelicates

The subtle balance between organized and chaotic domains in the nondiscoidal ligand in the helicate 1 , which displays liquid crystalline properties, represents the key element which enables the local molecular architecture to be integrated into an organized macroscopic ensemble.     

Metal‐Ion‐Induced Switch of Liquid‐Crystalline Orientation of Metallomacrocycles

A new series of shape‐persistent imine‐bridged macrocycles were synthesized based on dynamic covalent chemistry. The macrocycles had an alternating sequence of dibenzothiophene and N,N′‐bis(salicylidene)‐ethylenediamine (salen) tethering branched alkyl chains. The macrocycles and tetranuclear metallomacrocycles bearing long and branched alkyl chains exhibited thermotropic columnar liquid‐crystalline phases over a wide temperature range and the metallomacrocycles greatly depended on the characteristics of the coordinated metal ions. The metal‐free macrocycle showed a liquid‐crystalline phase with a lamellar structure and poor birefringence. In sharp contrast, the macrocyclic Ni complex showed a columnar oblique liquid‐crystalline phase, whereas the Pd and Cu complexes showed columnar liquid‐crystalline phases with a lamellar structure. The macroscopic organization and thermal properties of the corresponding liquid‐crystalline metallomacrocycles were significantly dependent on the subtle structural differences among the planar macrocycles, which were revealed by single‐crystal X‐ray crystallographic analysis of the macrocycles with shorter alkyl chains.     

Polymers in lyotropic liquid crystals

Polymers can be incorporated into lamellar liquid crystalline systems without the phenomena of macroscopic phase separation occurring. By playing with the inter-membrane interactions and the polymer–bilayer interactions the properties of the lamellar system can be modified significantly. This is not only of interest as a fundamental prerequisite to life, but it also opens new fields of application.     

Comparison of calculated and observed CD spectra of liquid crystalline dispersions formed from double-stranded DNA and from DNA complexes with coloured compounds

The CD spectra of dispersions of DNA, in the form of cholesteric liquid crystalline droplets, in an aqueous continuum have been studied. Calculated curves have been fitted to experimental spectra. The amplitude and the sign of the intense absorption band of the purine and pyrimidine bases vary with the droplet size, the pitch and the twist sense of the cholesteric phase. The CD spectra of dispersions of the complex formed by DNA and a coloured intercalating antibiotic have been similarly studied. A general satisfactory level of fitting between observed and calculated CD spectra was found.     

A NEW STRATEGY FOR THE DESIGN OF LIQUID CRYSTALLINE POLYMERS WITH FLEXIBLE AND APOLAR BUILDING BLOCKS

The synthesis and characterization of a new series of liquid crystalline polymers, poly(dicycloalkylvinylterephthalate)s, are reported. The basic building blocks of these polymers are not mesogenic by themselves. However,very stable mesophases can be generated by self-assembly of the polymer molecules. This approach suggests a novel designstrategy of liquid crystalline polymers with flexible and apolar building blocks.     

Sugar-based microemulsion glass templates

Complex fluids comprising of surfactants with water and/or oil form a rich variety of dynamic self-assembled structures, ranging from spherical swollen micelles, viscous rod-like micelles, and bicontinuous microemulsions to ordered liquid crystalline phases. The wide range of practical and specialized applications of complex fluids has made them the subject of intense research for many decades. Here, we demonstrate for the first time how bicontinuous microemulsions containing equal masses of oil and sugar can be driven to the glassy state without phase separation at ambient temperatures by controlled desiccation of sugar-rich microemulsions. The robust nanostructure of these microemulsion glasses allows polymerization of hydrophobic liquid monomers within the interstices of the glassy microemulsion template without macroscopic phase separation. Yet after polymerization, the sugar and surfactant template can be easily removed by dissolution in water.     

Lyotropic mesophase of cellulose in ammonia/ammonium thiocyanate solution

Solutions of cellulose in a mixture of 27:73 (w/w) of liquid ammonia and ammonium thiocyanate become liquid crystalline at room temperature above a certain critical concentration which depends on the degree of polymerization of the dissolved cellulose. The high optical rotations of the solution suggest that the cellulose mesophase is cholesteric in nature. In the two-phase region, the cellulose solutions exhibit negatively birefringent spherulites that possess both ringed and nonringed internal structures. The anisotropic solutions can be oriented by shear, indicating high potential for spinning them into useful fibers.     

Thermotropic Liquid Crystals Formed by Intermolecular Hydrogen Bonding Interactions

The role of hydrogen bonding in the formation or stabilization of liquid crystalline phases has only recently been appreciated. Following the first, wellestablished examples of liquid crystal formation from the dimerization of aromatic carboxylic acids, through hydrogen bonding, several classes of compounds have recently been synthesized, the liquid crystalline behavior of which is also dependent on intermolecular hydrogen bonds between similar or dissimilar molecules. In this review the main classes of compounds exhibiting liquid crystallinity due to hydrogen bonding are presented to show the diversity of organic compounds that can be used as building elements in liquid crystals. The molecules are either of the rigid-rod anisotropic or amphiphilic types such as molecules appropriately functionalized with pyridyl and carboxyl groups, whose interaction leads to the formation of liquid crystals; amphiphilic carbohydrates and amphiphilic and bolaamphiphilic compounds with multiple hydroxyl groups whose dimerization or association is indispensable for the formation of liquid crystals; and certain amphiphilic carboxylic acids with monomeric or polymeric mesogens and amphiphilic-type compounds bearing different moieties, whose interaction may lead to the formation of mesomorphic compounds. Associated with the macroscopic display of liquid crystalline phases is the supramolecular structure, and therefore rather extended discussion of these structures are included in this review.