Functional π-Gelators and Their Applications

Light-driven phenomena both in living systems and nonliving materials have enabled truly fascinating and incredible dynamic architectures with terrific forms and functions. Recently, liquid crystalline materials endowed with photoresponsive capability have emerged as enticing systems. In this Review, we focus on the developments of light-driven liquid crystalline materials containing photochromic components over the past decade. Design and synthesis of photochromic liquid crystals (LCs), photoinduced phase transitions in LC, and photoalignment and photoorientation of LCs have been covered. Photomodulation of pitch, polarization, lattice constant and handedness inversion of chiral LCs is discussed. Light-driven phenomena and properties of liquid crystalline polymers, elastomers, and networks have also been analyzed. The applications of photoinduced phase transitions, photoalignment, photomodulation of chiral LCs, and photomobile polymers have been highlighted wherever appropriate. The combination of photoc...

Light-Driven Liquid Crystalline Materials: From Photo-Induced Phase Transitions and Property Modulations to Applications.

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.

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

The theoretical study of a 3D photonic topological metacrystal based on an all-dielectric metamaterial platform shows robust propagation of surface states along 2D domain walls, making it a promising solution for photonics applications. The proposed metacrystal design might also open the way for the observation of elusive fundamental physical phenomena.

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Three-Dimensional All-Dielectric Photonic Topological Insulator

The synthesis and characterisation of the nonsymmetric liquid crystal dimer, 1-(4-cyanobiphenyl-4'-yloxy)-6-(4-cyanobiphenyl-4'-yl)hexane (CB6OCB) is reported. An enantiotropic nematic (N)-twist-bend nematic (NTB) phase transition is observed at 109 °C and a nematic-isotropic phase transition at 153 °C. The NTB phase assignment has been confirmed using polarised light microscopy, freeze fracture transmission electron microscopy (FFTEM), (2)H-NMR spectroscopy, and X-ray diffraction. The effective molecular length in both the NTB and N phases indicates a locally intercalated arrangement of the molecules, and the helicoidal pitch length in the NTB phase is estimated to be 8.9 nm. The surface anchoring properties of CB6OCB on a number of aligning layers is reported. A Landau model is applied to describe high-resolution heat capacity measurements in the vicinity of the NTB-N phase transition. Both the theory and heat capacity measurements agree with a very weak first-order phase transition. A complementary extended molecular field theory was found to be in suggestive accord with the (2)H-NMR studies of CB6OCB-d2, and those already known for CB7CB-d4. These include the reduced transition temperature, TNTBN/TNI, the order parameter of the mesogenic arms in the N phase close to the NTB-N transition, and the order parameter with respect to the helix axis which is related to the conical angle for the NTB phase.

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Understanding the twist-bend nematic phase: the characterisation of 1-(4-cyanobiphenyl-4′-yloxy)-6-(4-cyanobiphenyl-4′-yl)hexane (CB6OCB) and comparison with CB7CB

New chiral dimers consisting of a rod-like and cholesterol mesogenic units are reported to form a chiral twist-bend nematic phase (NTB*) with heliconical structure. The compressibility of the NTB phase made of bent dimers was found to be as large as in smectic phases, which is consistent with the nanoperiodic structure of the NTB phase. The atomic force microscopy observations in chiral bent dimers revealed a periodicity of about 50 nm, which is significantly larger than the one reported previously for non-chiral compounds (ca. 10 nm).

A Twist‐Bend Nematic (NTB) Phase of Chiral Materials

Dimeric compounds forming twist-bend nematic, Ntb, phase show unusual optical textures related to the formation of arrays of focal conic defects (FCDs). Some of the focal conics exhibit submicron internal structure with 8 nm periodicity, which is very close to that found in the crystalline phase of the material, that might suggest surface freezing.

Do the short helices exist in the nematic TB phase

Dimeric compounds forming twist-bend nematic, Ntb, phase show unusual optical texture related to the formation of arrays of focal conic defects. Some of the focal conics show submicron internal structure with 8 nm periodicity, which is very close to that found in the crystalline phase of the material, suggesting surface freezing.

Physical gels made of liquid crystalline B4 phase

Co-precipitation reaction followed by hydrothermal treatment were used to synthesise Eu3+ or Tb3+ doped LaPO4 nanorods, of 5–10 nm in width and 50–100 nm in length. Surface modification of the as-prepared nanoparticles with a selected luminescent organic compound resulted in formation of hybrid inorganic–organic nanomaterials. The products obtained exhibited tunable multicolour luminescence, dependent on the surface modification and applied excitation wavelength. The colour of their emission can be altered from red-orange to yellow-green. Powder X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM) and scanning transmission electron microscopy (STEM) confirmed the structure and morphology of the products synthesized. Successful surface modification of the nanophosphors was evidenced by analytical and spectroscopic techniques such as dynamic light scattering (DLS) – providing size distribution histograms and zeta potentials of the nanoparticles; IR spectroscopy and elemental analysis which proved the presence of an organic phase in the structure; spectrofluorometry (excitation/emission spectra and luminescence decay curves) which confirmed the formation of hybrid, surface modified nanomaterials revealing tunable multicolour emission.

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Anna Zep

Papers

A Twist‐Bend Nematic (NTB) Phase of Chiral Materials

Do the short helices exist in the nematic TB phase

Do the short helices exist in the nematic TB phase

Physical gels made of liquid crystalline B4 phase

Eu3+ and Tb3+ doped LaPO4 nanorods, modified with a luminescent organic compound, exhibiting tunable multicolour emission