Chiral differentiation of limonene in chiral nematic liquid crystals.

Chirality is of great importance in physical and biological systems. It helps differentiate chemical reactions and physical processes. It was reported that the diffusion of mesogenic chiral guests in chiral nematic liquid crystal hosts profoundly depends on the chirality of the guest and host molecules. When the guest and host molecules have the same handedness, the diffusion is much faster than that when the guest and host molecules have the opposite handedness. In this paper, we report the discovery that chiral differentiation also exists in the diffusion of limonene, which is non-mesogenic in chiral nematic liquid crystals. The diffusion of l-limonene (right-handed) in chiral nematic liquid crystals with a right handed helical structure is faster than that of d-limonene (left-handed). This result might be important in understanding the effects of chirality on physical processes that take place in biological systems. In addition, this effect could be utilized for enantiomer separation in the pharmaceutical industry.

Image flickering-free polymer stabilized fringe field switching liquid crystal display.

Liquid crystal displays are the leading technology for flat panel displays. Their energy efficiency is low, however, due to the light absorption caused by polarizers and color filters and power consumption by driving circuitries. In displaying static images, their energy efficiency can be improved if a low driving frequency is used. As the driving frequency is decreased, the transmittance of the displays may change with time, a phenomenon known as image flickering. In this research we demonstrated that polymer stabilization can significantly reduce the flickering in fringe field switching (FFS) liquid crystal display. Under the polymer stabilization, the driving voltage remains low and the response time becomes shorter. Through simulation study, we find that the polymer stabilization smooths the spatial variation of the liquid crystal orientation in the display, and thus reduce the flexoelectric effect which is responsible for image flickering. The polymer stabilization can be implemented in the current main stream manufacturing to produce displays that can show static images under low power consumption.

Effect of biaxiality on chirality in chiral nematic liquid crystals.

Biaxiality and chirality are two of the most interesting topics in materials and biological science, particularly in liquid crystals. What is even more interesting is that these two properties are related. It was theoretically predicted that morphological chirality is impossible without morphological biaxiality in chiral nematic liquid crystals. We experimentally study the effect of biaxiality on chirality. We show that when achiral liquid crystal dimers with large molecular biaxiality are doped into chiral nematic liquid crystals, their helical pitch is significantly decreased. We have also observed an abnormal fingerprint texture of the chiral nematic liquid crystal doped dimers, which suggests morphological biaxiality. Our experimental results support the biaxial theory of chiral nematic liquid crystals.

Selective scattering polymer dispersed liquid crystal film for light enhancement of organic light emitting diode.

We developed a novel light enhancing film for an organic light emitting diode (OLED) based on polymer dispersed liquid crystal (PDLC). In the film, the liquid crystal droplets are unidirectionally aligned along the film normal direction and exhibit selective scattering. The film scatters light emitted only in directions with large incident angles but not light emitted in directions with small incident angles. When the light is scattered, it changes propagation direction and exits the OLED. The PDLC film reduces the total internal reflection and thus can significantly increase the light efficiency of the OLED.

Flexoelectric in-plane switching (IPS) mode with ultra-high-transmittance, low-voltage, low-frequency, and a flicker-free image.

The demands for a power-saving mode for displaying static images are ubiquitous not only in portable devices but also in price tags and advertising panels. At a low-frequency driving in liquid crystal displays (LCDs) for low-power consumption, the flexoelectric effect arises even in calamitic liquid crystals and the optical appearance of this physical phenomenon is found to be unusually large, being noticed as an image-flickering. Although the inherent integrated optical transmittance of in-plane switching (IPS) mode is relatively lower than that of fringe-field switching (FFS) mode, the IPS mode shows no static image-flickering but an optical spike (the so-called optical bounce), at the transient moment between signal positive and negative frames. Here, we demonstrate an IPS mode using negative dielectric anisotropy of liquid crystals (Δε < 0) and fine-patterned electrodes (the width w of and the space l between electrodes ≤ 3 µm) with reduced operation voltage (up to 40.7% to a conventional FFS mode with Δε < 0), reduced optical bounce (up to 4.4%. to a conventional FFS mode with Δε < 0) and enhanced transmittance (up to 32.1% to a conventional IPS mode with Δε > 0). We believe the result will contribute not only to the scientific understanding of the optical appearance of flexoelectric effect but also pave the way for engineering of a superior low-power consumption LCD.

Full color waveguide liquid crystal display.

We developed a waveguide liquid crystal display from a liquid crystal (LC)/polymer composite. It does not need polarizers or color filters. It is illuminated by color LEDs installed on its edge. The light produced by the edge LEDs is coupled into the display and then waveguided through the display. When the LC is in the transparent state, the incident light is waveguided through and no light comes out of the viewing side of the display. When the LC is in the scattering state, the incident light is scattered and comes out of the display. It can be used either for transparent display or for direct view display. The composite has a submillisecond response time, and a field sequential scheme can be used to display full color images. Because the display does not need polarizers or color filters, its energy efficiency is much higher than current liquid crystal displays.

Stabilized electrically induced Helfrich deformation and enhanced color tuning in cholesteric liquid crystals.

When subjected to an AC electric field perpendicular to its layers, the cholesteric planar state may undergo a periodic layer undulation, known as the Helfrich deformation, which generates a color change of the reflected light. The Helfrich deformation of regular cholesteric liquid crystals is, however, unstable and easily taken over by the focal conic state, and thus the color tuning range is narrow. We demonstrated that the Helfrich deformation can be stabilized in a large electric field region by doping a bent dimer with an anomalously small bend elastic constant and dispersing a small amount of polymer network. By varying the dimer concentration, we were able to systematically change the bend elastic constant and thus verify the theoretical prediction of the undulation threshold electric field and periodicity. We also achieved reflectance tuning with electric field less than 2 V µm-1 and color tuning covering the entire visible light region with electric field as low as 4 V µm-1.

HOXA13 is associated with unfavorable survival and acts as a novel oncogene in prostate carcinoma.

AIM: To investigate the clinical relevance and functional role of HOXA13 in prostate cancer Methods: PCR, western blot and immunohistochemistry were performed to determine the expression. Kaplan-Meier and Cox regression survival analyses investigated the clinical relevance. Cell viability, flow cytometry and transwell assays were used to determine the functional roles. RESULTS: HOXA13 expression is sharply increased in carcinoma tissues and is significantly associated with poor prognosis of prostate cancer patients. Interestingly, nucleus not cytoplasm HOXA13 expression is associated with unfavorable survival of the patients. Furthermore, nucleus HOXA13 expression represents an unfavorable and independent prognosis factor of histological grade 2 or Gleason grade <8 patients. Functionally, forced expression of HOXA13 obviously promotes tumor cell proliferation, migration and invasion, whereas inhibits tumor cell apoptosis. CONCLUSION: HOXA13 is an unfavorable prognostic factor and a novel oncogene for prostate cancer.

Field-symmetrization to solve luminance deviation between frames in a low-frequency-driven fringe-field switching liquid crystal cell.

The development of low-frequency-driven liquid crystal displays (LCDs) has recently received intense attention to open up low-power consumption display devices, such as portable displays, advertising panels and price tags. In fringe-field switching (FFS) LCD mode, a unidirectional electric field gives rise to head-tail symmetry breaking in liquid crystals, so that the flexoelectric effect, a coupling between the elastic distortion and the electric polarization, becomes enormously significant. The effect is thus linked to an unusual optical effect, which badly damages the quality of images by image-flickering, and this image-flickering is mainly caused by transmittance difference between the applied signal frames. Here, we intensively investigate the mechanism of the transmittance deviation, and propose an essential and promising approach to solve the poor image-quality, that is, symmetrization of electric fields between the frames. The result of our work clearly demonstrates that the field-symmetry is crucial to reduce the image-flickering, and it can be obtained by optimization of the thickness of an insulation layer with respect to the ratio of the space between electrodes to the electrode width.

Single-cell gap polymer-stabilized fringe-field switching transflective liquid crystal display.

Transflective liquid crystal displays are highly desired for mobile devices because they can be operated either in transmissive mode, illuminated by backlight in dark ambient light conditions, or reflective mode, illuminated by ambient light in bright ambient light conditions. We developed a single-cell gap transflective display based on fringe-field switching. The display consists of transmissive and reflective subpixels whose operations are synchronized through polymer stabilization. This display has a high contrast ratio because the transmittance-voltage dependences of the two subpixels are similar (they are both in dark state at 0 V and in bright state at an applied voltage) and do not interfere with each other. It has the advantages of single-cell gap and no in-cell retarder and its manufacturing process is simple.

Matched elastic constants for a perfect helical planar state and a fast switching time in chiral nematic liquid crystals.

Chiral nematic liquid crystals possess a self-assembled helical structure and exhibit unique selective reflection in visible and infrared light regions. Their optical properties can be electrically tuned. The tuning involves the unwinding and restoring of the helical structure. We carried out an experimental study on the mechanism of the restoration of the helical structure. We constructed chiral nematic liquid crystals with variable elastic constants by doping bent-dimers and studied their impact on the restoration. With matched twist and bend elastic constants, the helical structure can be restored dramatically fast from the field-induced homeotropic state. Furthermore, defects can be eliminated to produce a perfect planar state which exhibits high selective reflection.

[Efficacy and safety of Yimusake Tablets plus dapoxetine hydrochloride in the treatment of premature ejaculation].

OBJECTIVE: To evaluate the effect and safety of Yimusake Tablets combined with dapoxetine hydrochloride and either of them used alone in the treatment of premature ejaculation (PE). METHODS: We randomly assigned 180 PE patients to oral medication of Yimusake Tablets at 1.5 g per night (group A), dapoxetine hydrochloride at 30 mg at 1－3 hours before anticipated sexual activity (group B), the Yimusake Tablets plus dapoxetine hydrochloride simultaneously (group C), all for 8 weeks. After 4 and 8 weeks of medication, we recorded and compared the changes in the intravaginal ejaculation latency time (IELT), measures of the PE profile (PEP), and adverse events among the three groups of patients. RESULTS: The treatment was accomplished and complete data obtained from 154 of the patients, 56 in group A, 52 in group B, and 46 in group C. After 4 and 8 weeks of medication, the mean IELT was dramatically prolonged in all the three groups as compared with the baseline (P<0.01), most significantly at 8 weeks in group C (ï¼»2.08±0.68ï¼½ min), followed by B (ï¼»1.76±0.52ï¼½ min) and A (ï¼»1.47±0.44ï¼½ min), with statistically significant differences among the three groups (P<0.01). The PEP measures were remarkably improved in group A at 8 weeks (P<0.05), and both in B and C at 4 and 8 weeks (P<0.05), most significantly at 8 weeks in group C (P<0.05), in which the patients scored 1.96±0.77 in perception of control over ejaculation, 2.62±0.98 in satisfaction with sexual intercourse, 3.04±0.62 in PE-related distress, and 3.57±0.80 in PE-induced difficult relationship with their partners, all markedly improved as compared with groups A and B (P<0.05). Adverse reactions were observed in 2 cases (3.6%) in group A, 6 cases (9.6%) in B, and 5 cases (10.9%) in C. No severe adverse events occurred in any of the patients during the study. CONCLUSIONS: Combined medication of Yimusake Tablets and dapoxetine hydrochloride, with its advantages of effectiveness and safety, deserves to be recommended for the treatment of PE.

Light-Driven Reversible Alignment Switching of Liquid Crystals Enabled by Azo Thiol Grafted Gold Nanoparticles.

Stimuli-directed alignment control of liquid crystals (LCs) with desired molecular orientation is currently in the limelight for the development of smart functional materials and devices. Here, photoresponsive azo thiol (AzoSH) was grafted onto gold nanoparticles (GNPs). The resulting hybrid GNPs were able to homogeneously mix with a commercially available nematic LC host, as evidenced by Cryo-TEM. Interestingly, the LC nanocomposites were found to undergo reversible alignment transition upon light irradiation as a consequence of the trans-cis photoisomerization of the azo groups on the GNP surface. LC molecules in either planar or bare glass cells were able to change their alignment to vertical upon UV irradiation, while the vertically aligned LC molecules returned to the planar or random orientation under visible irradiation. Neither the azo thiol molecules nor the unfunctionalized GNPs alone promoted the alignment of the LC molecules in the system upon light irradiation. The photoinduced vertical alignment without applied electric or magnetic field was very stable over time and with respect to temperature. Furthermore, an optically switchable device based on the photostimulated reversible alignment control of LCs was demonstrated.

Mechanism of electrically induced photonic band gap broadening in polymer stabilized cholesteric liquid crystals with negative dielectric anisotropies.

We experimentally observed that the photonic band gap (reflection band) of polymer stabilized cholesteric liquid crystals with negative dielectric anisotropies can be greatly broadened under DC electric fields. We explored the underlying mechanism. We found that the dispersed polymer network moved when DC voltages were applied across the liquid crystal cell. The motion of the polymer network stretched the helical pitch of the liquid crystal on one side of the cell and compressed the helical pitch on the other side of the cell. We proposed a phenomenological theory to explain the motion of the polymer network and the effect of the polymer network on the helical pitch, and this theoretical prediction agreed well with the experimental results.

Light-directing omnidirectional circularly polarized reflection from liquid-crystal droplets.

Constructing and tuning self-organized three-dimensional (3D) superstructures with tailored functionality is crucial in the nanofabrication of smart molecular devices. Herein we fabricate a self-organized, phototunable 3D photonic superstructure from monodisperse droplets of one-dimensional cholesteric liquid crystal (CLC) containing a photosensitive chiral molecular switch with high helical twisting power. The droplets are obtained by a glass capillary microfluidic technique by dispersing into PVA solution that facilitates planar anchoring of the liquid-crystal molecules at the droplet surface, as confirmed by the observation of normal incidence selective circular polarized reflection in all directions from the core of individual droplet. Photoirradiation of the droplets furnishes dynamic reflection colors without thermal relaxation, whose wavelength can be tuned reversibly by variation of the irradiation time. The results provided clear evidence on the phototunable reflection in all directions.

Structure and optical properties of twist-bend nematic liquid crystals doped with chiral dopants.

Twist-bend nematic liquid crystals (N_{TB} LCs), although consisting of achiral molecules, possess a spontaneous conic helix. They have been intensively studied and utilized in many applications in recent years. Herein we add chiral molecules to N_{TB} LCs and study their effects on the structure of the conic helix. We observe that the system is in the regular chiral nematic phase at high temperature and is still in the twist-bend nematic phase at low temperature. The addition of the chiral molecules does not induce a twist of the conic helical axis. The main effect of the chiral molecules is increasing the cone angle of the conic helix. We show that the structural chirality parameters in the chiral nematic phase and the twist-bend chiral nematic phase can be calculated from the same intrinsic chirality parameter, which only depends on the molecular structure and concentrations of the chiral molecule. We also observe a pretransitional phenomenon that the helical pitch of the chiral nematic phase increases dramatically when temperature is decreased toward the chiral nematic to twist-bend nematic phase transition temperature.

Bis{5-[(2-propyn-1-yl-oxy)meth-yl]-1,3-phenyl-ene}-32-crown-10.

The mol-ecule of the title compound {systematic name: 17,35-bis-[(2-propyn-1-yl-oxy)meth-yl]-2,5,8,11,14,20,23,26,29,32-deca-oxatricyclo-[31.3.1.1(15,19)]octa-triaconta-1(37),15,17,19 (38),33,35-hex-a--ene}, C(36)H(48)O(12), has crystallographic inversion symmetry and adopts a chair-like conformation. The polyether bridges of the macrocycle adopt gauche conformations and the cavity of the macrocycle is collapsed. In the crystal structure, there are weak inter-molecular C-H⋯O hydrogen bonds driven in part by the elevated acidity of acetylenyl H atoms.

Light-driven reversible handedness inversion in self-organized helical superstructures.

We report here a fast-photon-mode reversible handedness inversion of a self-organized helical superstructure (i.e., a cholesteric liquid crystal phase) using photoisomerizable chiral cyclic dopants. The two light-driven cyclic azobenzenophanes with axial chirality show photochemically reversible trans to cis isomerization in solution without undergoing thermal or photoinduced racemization. As chiral inducing agents, they exhibit good solubility, high helical twisting power, and a large change in helical twisting power due to photoisomerization in three commercially available, structurally different achiral liquid crystal hosts. Therefore, we were able to reversibly tune the reflection colors from blue to near-IR by light irradiation from the induced helical superstructure. More interestingly, the different switching states of the two chiral cyclic dopants were found to be able to induce a helical superstructure of opposite handedness. In order to unambiguously determine the helical switching, we employed a new method that allowed us to directly determine the handedness of the long-pitched self-organized cholesteric phase.

Patterned waveguide liquid crystal displays.

We report a novel polymer stabilized liquid crystal based light waveguide display whose performance is significantly improved by using patterned photo-polymerization or an electrode. The waveguide display is edge-lit and operates on the light scattering of the polymer stabilized liquid crystal. When no voltage is applied, the liquid crystal is uniformly aligned and is transparent. The incident light is waveguided through the display by total internal reflection and no light comes out of the viewing side of the display. When a voltage is applied, the liquid crystal is switched to a micron-sized poly-domain structure and becomes scattering. The incident light is scattered out of the viewing side of the display. We demonstrated that by using patterned photo-polymerization or an ITO electrode, the scattering efficiency of the liquid crystal in the voltage-on state is significantly enhanced. We have achieved high brightness, low driving voltage, sub-millisecond switching time and high contrast ratio. This new display is suitable for transparent and augmented display applications.

Structure of liquid crystal droplets with chiral propeller texture.

We experimentally studied a nematic liquid crystal whose molecules form twisted head-to-head H-bonded dimers. We observed that when the material transformed from the isotropic to nematic phase, it formed droplets with chiral propeller textures. We carried out a computer simulation to investigate the liquid crystal director configuration inside the droplets and to study the effects of elastic constants and chirality on the droplet texture. Results of our study show it is likely that the material in the droplets had nonzero chirality due to spontaneous chiral phase separation.