Fluorescence Confocal Polarizing Microscopy of a Fluorescent Bent-Core Liquid Crystal Exhibiting Polarization Splay Modulated (B7) Structures and Defects

Is the origin of green fluorescence in unsymmetrical four-ring bent-core liquid crystals single or double proton transfer?

The origin of green fluorescence in unsymmetrical four-ring bent-core liquid crystals (BCLCs) is not understood clearly.

Structural Understanding, Photoswitchability, and Supergelation of a New Class of Four Ring-Based Bent-Shaped Liquid Crystal

Herein, we report a new type of azobenzene-based unsymmetrical bent-core molecules exhibiting photoswitchability in the liquid crystalline state, solid state, and solution state and in mixture upon UV irradiation and intense visible light. The compounds exhibited solid-state photochromism upon exposure to UV light, whereas in liquid crystalline state, reversible phase transitions were observed via both UV irradiation and intense visible light exposure. Crystal structure analysis reveals the basic structural understanding such as nonplanar bent molecular shape, antiparallel arrangement of the polar bent molecules, intra- and intermolecular hydrogen bonding, and different π-π interactions and interdigitation of long alkyl chains. The compounds are also found to act as supergelator toward various organic solvents. Hence, this is an excellent example of such potential bent-shaped liquid crystals that promise an immense perspective for device applications such as optical storage, molecular switches, etc.

B7 Liquid Crystal Filament Growth in Presence of Carbon Nanotubes

Liquid crystal phases formed from bent-core mesogens have attracted much interest of the liquid crystal research community, due to the manifestation of chirality effects from achiral molecules. One of the most elusive of the bent-core phases is the B7 phase, which at its early stage often forms in a helical filament fashion. We investigate the growth of such filaments in the presence of single-walled nanotubes to elucidate possible effects on the growth dynamics and helicity of B7 helical filaments. It is found that the filament width slightly decreases in comparison to the neat B7 material, suggesting a more tightly bound structure around the nanotubes, with the nanotubes likely acting as the core of the helical filament. No effects on pitch or periodicity of the helical superstructure is observed. The filament growth velocity quickly decreases as nanotubes are added to the B7 phase, indicating that a more tightly bound structure needs a longer time of formation. An observed buckling instability is of interest as a microscopic example for the study of nonlinear dynamics theories of filaments. The present investigation is thus of general importance for nanoparticle directed growth of filaments, which has applications in biomolecular growth and high tensile strength fibres.

Origin of green photoluminescence in four-ring bent-core molecules with ESIPT, selective sensing of zinc ions by turn-on emission and their liquid crystal properties

Fluorescent four-ring symmetrical/unsymmetrical molecules containing alkyl chains of a varied number of –CH₂– groups with a bent-core have been synthesized to explore their liquid crystalline (LC) and photophysical properties.

Airflow-aligned helical nanofilament (B4) phase in topographic confinement

We investigated a controlled helical nanofilament (HNF: B4) phase under topographic confinement with airflow that can induce a shear force and temperature gradient on the sample. The resulting orientation and ordering of the B4 phase in this combinational effort was directly investigated using microscopy. The structural freedom of the complex B7 phase, which is a higher temperature phase than the B4 phase, can result in relatively complex microscopic arrangements of HNFs compared with the B4 phase generated from the simple layer structure of the B2 phase. This interesting chiral/polar nanofilament behaviour offers new opportunities for further exploration of the exotic physical properties of the B4 phase.

Highly Polarized Fluorescent Illumination Using Liquid Crystal Phase

Liquid crystal (LC) materials are currently the dominant electronic materials in display technology because of the ease of control of molecular orientation using an electric field. However, this technology requires the fabrication of two polarizers to create operational displays, reducing light transmission efficiency below 10%. It is therefore desirable to develop new technologies to enhance the light efficiency while maintaining or improving other properties such as the modulation speed of the molecular orientation. Here we report a uniaxial-oriented B7 smectic liquid crystalline film, using fluorescent bent-core LC molecules, a chemically modified substrate, and an in-plane electric field. A LC droplet under homeotropic boundary conditions of air/LC as well as LC/substrate exhibits large focal conic like optical textures. The in-plane electric field induced uniaxial orientation of the LC molecules, in which molecular polar directors are aligned in the direction of the electric field. This highly oriented LC film exhibits linearly polarized luminescence and microsecond time-scale modulation characteristics. The resultant device is both cheap and easy to fabricate and thus has great potential for electro-optic applications, including LC displays, bioimaging systems, and optical communications.