Photopolymerization of Reactive Amphiphiles: Automatic and Robust Vertical Alignment Layers of Liquid Crystals with a Strong Surface Anchoring Energy

A photopolymerizable itaconic acid-based amphiphile (abbreviated as Ita3C₁₂) consisting of a hydrophilic carboxylic acid, three alkyl tails, and a reactive vinyl function was newly designed and synthesized for the formation of automatic and robust vertical alignment (VA) layer of nematic liquid crystals (NLC). Since a hydrophilic carboxylic acid was chemically attached to the end of Ita3C₁₂, the Ita3C₁₂ amphiphiles initially dissolved in the host NLC medium were migrated toward the substrates for the construction of VA layer of NLC. The alkyl tails of Ita3C₁₂ in the VA layer directly interacted with host NLC molecules and made them to automatically align vertically. Because of the reactive vinyl functions of Ita3C₁₂ amphiphiles, it was possible to stabilize the automatic VA layer by the photopolymerization with methacryl polyhedral oligomeric silsesquioxane (MAPOSS) cross-linkers. The polymer-stabilized robust Ita3C₁₂ VA layer exhibited a strong surface anchoring energy without generating any light scatterings. The automatic fabrication of robust LC alignment layers can allow us to reduce the manufacturing cost and to open new doors for electro-optical applications

Construction of Polymer-Stabilized Automatic MultiDomain Vertical Molecular Alignment Layers with Pretilt Angles by Photopolymerizing Dendritic Monomers under Electric Fields

The synthesized itaconic acid-based dendritic amphiphile (Ita3C₁₂) monomers and the methacryl polyhedral oligomeric silsesquioxane (MAPOSS) cross-linkers were directly introduced for the construction of automatic vertical alignment (auto-VA) layers in the host nematic liquid crystal (NLC) medium. The auto-VA layer can be stabilized by irradiating UV light. For the automatic fabrication of a polymer-stabilized multidomain VA (PS auto-MDVA) layer with a pretilt angle, Ita3C₁₂ and MAPOSS were photopolymerized under the electric field by irradiating UV light on the multidomain electrode cell. Mainly because of the pretilted NLC at zero voltage, the electro-optic properties of the PS auto-MDVA cell were dramatically improved. From the morphological observations combined with surface chemical analyses, it was found that various sizes of protrusions on the solid substrates were automatically constructed by the two-step mechanisms. We demonstrated the PS auto-MDVA cell with the enhancement of electro-optic properties as a single-step process and investigated how the protrusions were automatically developed during the polymer stabilization

Pyrene-Based Asymmetric Supramolecule: Kinetically Controlled Polymorphic Superstructures by Molecular Self-Assembly

To understand the kinetically controlled polymorphic superstructures of asymmetric supramolecules, a pyrene-based asymmetric supramolecule (abbreviated as Py3M) was newly synthesized by connecting two pyrene headgroups (Py) to a biphenyl-based dendritic tail (3M) with an iso­phthala­mide connector. On the basis of thermal, microscopic, spectroscopic, and scattering results, it was realized that Py3M exhibited the monotropic phase transition between a stable crystalline phase (K1) and a metastable crystalline phase (K2). This monotropic phase transition behavior was mainly originated from the competitions of intra- and intermolecular interactions (π–π interactions and hydrogen bonds) as well as from the nanophase separations. From the two-dimensional (2D) wide-angle X-ray diffraction patterns and transmission electron microscopy images of the self-assembled Py3M superstructures, it was found that Py3M formed two synclinically tilted crystalline superstructures: the 6.75 and 4.4 nm periodicities of layered structures for K1 and K2 phases, respectively. The stable K1 phase was predominantly induced by the π–π interactions between pyrenes, while the intermolecular hydrogen bonds between iso­phthala­mides were the main driving forces for the formation of the metastable K2 phase. Ultraviolet–visible and photoluminescence experiments indicated that the photophysical properties of Py3M were directly related to their molecular packing superstructures

Flexible and Patterned Thin Film Polarizer: Photopolymerization of Perylene-based Lyotropic Chromonic Reactive Mesogens

A perylene-based reactive mesogen (DAPDI) forming a lyotropic chromonic liquid crystal (LCLC) phase was newly designed and synthesized for the fabrication of macroscopically oriented and patterned thin film polarizer (TFP) on the flexible polymer substrates. The anisotropic optical property and molecular self-assembly of DAPDI were investigated by the combination of microscopic, scattering and spectroscopic techniques. The main driving forces of molecular self-assembly were the face-to-face π–π intermolecular interaction among aromatic cores and the nanophase separation between hydrophilic ionic groups and hydrophobic aromatic cores. Degree of polarization for the macroscopically oriented and photopolymerized DAPDI TFP was estimated to be 99.81% at the <i><b>λ</b></i>_max = 491 nm. After mechanically shearing the DAPDI LCLC aqueous solution on the flexible polymer substrates, we successfully fabricated the patterned DAPDI TFP by etching the unpolymerized regions selectively blocked by a photomask during the photopolymerization process. Chemical and mechanical stabilities were confirmed by the solvent and pencil hardness tests, and its surface morphology was further investigated by optical microscopy, atomic force microscopy, and three-dimensional surface nanoprofiler. The flexible and patterned DAPDI TFP with robust chemical and mechanical stabilities can be a stepping stone for the advanced flexible optoelectronic devices

Azobenzene Molecular Machine: Light-Induced Wringing Gel Fabricated from Asymmetric Macrogelator

To develop light-triggered wringing gels, an asymmetric macrogelator (1AZ3BP) was newly synthesized by the chemically bridging a photoisomerizable azobenzene (1AZ) molecular machine and a biphenyl-based (3BP) dendron with a 1,4-phenylenediformamide connector. 1AZ3BP was self-assembled into a layered superstructure in the bulk state, but 1AZ3BP formed a three-dimensional (3D) network organogel in solution. Upon irradiating UV light onto the 3D network organogel, the solvent of the organogel was squeezed and the 3D network was converted to the layered morphology. It was realized that the metastable 3D network organogels were fabricated mainly due to the nanophase separation in solution. UV isomerization of 1AZ3BP provided sufficient molecular mobility to form strong hydrogen bonds for the construction of the stable layered superstructure. The light-triggered wringing gels can be smartly applied in remote-controlled generators, liquid storages, and sensors

Self-Assembled Hierarchical Superstructures from the Benzene-1,3,5-Tricarboxamide Supramolecules for the Fabrication of Remote-Controllable Actuating and Rewritable Films

The well-defined hierarchical superstructures constructed by the self-assembly of programmed supramolecules can be organized for the fabrication of remote-controllable actuating and rewritable films. To realize this concept, we newly designed and synthesized a benzene-1,3,5-tricarboxamide (BTA) derivative (abbreviated as BTA-3AZO) containing photoresponsive azobenzene (AZO) mesogens on the periphery of the BTA core. BTA-3AZO was first self-assembled to nanocolumns mainly driven by the intermolecular hydrogen-bonds between BTA cores, and these self-assembled nanocolumns were further self-organized laterally to form the low-ordered hexagonal columnar liquid crystal (LC) phase below the isotropization temperature. Upon cooling, a lamello-columnar crystal phase emerged at room temperature via a highly ordered lamello-columnar LC phase. The three-dimensional (3D) organogel networks consisted of fibrous and lamellar superstructures were fabricated in the BTA-3AZO cyclohexane-methanol solutions. By tuning the wavelength of light, the shape and color of the 3D networked thin films were remote-controlled by the conformational changes of azobenzene moieties in the BTA-3AZO. The demonstrations of remote-controllable 3D actuating and rewritable films with the self-assembled hierarchical BTA-3AZO thin films can be stepping stones for the advanced flexible optoelectronic devices

Asymmetric Organic–Inorganic Hybrid Giant Molecule: Cyanobiphenyl Monosubstituted Polyhedral Oligomeric Silsesquioxane Nanoparticles for Vertical Alignment of Liquid Crystals

For liquid crystal (LC) alignment, polyhedral oligomeric silsesquioxanes (POSS) can be considered as one of the promising candidates for the formation of vertical alignment (VA) of LC. However, because of their poor compatibility and weak interaction with LC hosts, the pristine POSS are highly aggregate themselves in the LC media and create the macroscopic particles, resulting in severe light scatterings. To overcome this barrier, we proposed and successfully synthesized the cyanobiphenyl monosubstituted POSS giant molecule (abbreviated as POSS-CBP₁), which showed an excellent dispersion in nematic (N) LC media and formed the perfect VA of LC without using conventional polymer-based VA layers. On the basis of the systematic experiments and careful analysis, we realized that the cyanobiphenyl moiety chemically attached to the pristine POSS with an alkyl chain can significantly improve the initial solubility and interaction with LC media but finely tune POSS-CBP₁ to gradually diffuse onto the substrate of LC cell for the formation of VA layer without forming the macroscopic aggregations. Therefore, the newly developed POSS-CBP₁ VA layer can allow us to significantly cut the manufacturing cost as well as to open the new doors for electro-optical applications