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Reversible photochromic phase transition of non-planar dithienylcyclopentene-containing liquid crystalline molecules has been studied in this work. All materials showed the smectic A and nematic phases in the cooling process and had reversible and high interconversion yield >90% between colourless-open/blue-closed isomers in the liquid crystalline state as well as in solution by UV- and visible light-irradiation alternatively, as confirmed by nuclear magnetic resonance spectroscopy, polarised optical microscopy, differential scanning calorimetry, powder X-ray diffraction and UV-visible spectroscopy. The thermal stability of both isomers also ensures that they can maintain liquid crystalline phases during ring-open and ring-closure reactions. Their birefringence is between 0.1 and 0.2, which is comparable to that of standard liquid crystalline materials used in optical applications. [ABSTRACT FROM AUTHOR]

Highlights from the article: The 27th International Liquid Crystal Conference (ILCC2018) was held in Kyoto from 22 to 27 July 2018. Considering this fact, the organising committee planned general sessions for existing fields of science and technology of liquid crystals as well as special sessions for research fields related to liquid crystals and industrial applications in order to extend the territory of liquid crystal science and technology. Diverse topics were covered in the session ranging from defects, liquid crystal composites, molecular theories of complex phases, biological and lyotropic liquid crystals, and elastomers. The International Liquid Crystal Conferences have provided excellent opportunities for sharing new ideas, stimulating discussions, and exchange of information for researchers and engineers in the fields of liquid crystal science and technology since the first conference was held in Kent State University in 1965.

Liquid crystal micro-particles are functional materials possessing optical and dielectric anisotropies due to their inner molecular alignment, and are fabricated by polymerizing pre-aligned molecules in the liquid crystalline state. In this study, we demonstrate field-induced rotation of liquid crystal micro-particles in a nematic host and present a theoretical model that describes both the response of the surrounding liquid crystal host as well as micro-particles. We also investigate by experiment and theory that the decay time of the host liquid crystal in the vicinity of particles is faster than that of the host where the particles is absent. [ABSTRACT FROM AUTHOR]

Singular optics is an emerging field, in which an optical wave with a helical wavefront is handled for optical manipulation and nanofabrication. We present a method to generate optical vortices via reflection from cholesteric liquid crystals with planar alignment. Numerical and experimental results show that the device is operable at multiple wavelengths with theoretically high conversion efficiency (lossless) without requiring fine-control of retardation. Although the operational wavelength range is limited by the birefringence and helix pitch of the material, broadband operation is possible by expanding the reflection band width by either introducing a pitch distribution or stacking multiple devices. [ABSTRACT FROM AUTHOR]

We report the synthesis of liquid crystalline materials, which repeatedly liquefied and solidified when irradiated with ultraviolet (UV) and visible light at room temperature. The materials are the derivatives of the sugar alcohols, D-mannitol, D-sorbitol, and allitol, in which all hydroxyl groups were substituted with multi-mesogenic azobenzenes. The thermal phase transition behavior and stability of the liquid crystal phase were changed according to the sugar alcohols, but photochemical phase transition behaviors were not different. In addition, when applied as an adhesive layer to glass substrates, the materials exhibited changes in the adhesion force when irradiated with light. [ABSTRACT FROM PUBLISHER]

We focus on liquid crystals (LCs) doped with deoxyribonucleic acid (DNA). We have researched the effect of the single strand DNA doping on the LC molecular alignment structure in terms of the kind of base (adenine, thymine, guanine, and cytosine), the concentration, and the molecular weight of DNA. As a result, it is found that the DNA doping can induce a twist deformation of LC alignment. Furthermore, the twisted structure strongly depends on the kind of DNA base. [ABSTRACT FROM PUBLISHER]

Cholesteric liquid crystals selectively reflect circularly polarised light with the same handedness as the helix. Because of their sensitivity to external stimuli, such as heat and electrical fields, various applications utilising their tunability have been proposed. Tuning is usually performed in the bulk, meaning that cholesteric liquid crystals usually possess a single pitch throughout the medium. However, when the helical structure is locally modulated, different optical properties arise, such as tunable photonic defect modes and multiple reflection bands. Here we show a technique to locally modulate the helical structure of cholesteric liquid crystals on a submicron scale, based on two-photon excitation direct laser lithography. Two examples of cholesteric liquid crystal structures with modulated helical structures will be presented. [ABSTRACT FROM AUTHOR]

1,4,8,11,15,18,22,25-hexahexylphthalocyanine was studied on the carrier mobility characteristics by a Time-Of-Flight (TOF) technique. The compound exhibits an ambipolar nature of charge transport and the carrier mobilities for hole and electron were determined to be 0.3 and 0.2 cm2 V−1 s−1 in the hexagonal disordered columnar (Colhd ) mesophase and 0.3–1.4 and 0.4–0.5 cm2 V−1 s−1 in the crystal. These values were obtained for poly-domain films. A possibility of 2-dimensional transport of carriers was discussed in terms of the molecular structure and orderings in both Colhd and crystal phases. [ABSTRACT FROM AUTHOR]

We report electric field tuning of surface plasmon resonance (SPR) by controlling the polarization state of incident light using vertical alignment liquid crystal (VA-LC) layer. Excitation of SPR depends on the polarization state of incident light and incident angle. We fabricated a metallic grating structure in order to excite SPR, and then we investigated the applied voltage dependence of reflection spectrum. Continuous tuning of SPR is achieved as a result of the polarization change of incident light by controlling the birefringence of the LC layer. [ABSTRACT FROM AUTHOR]

The article offers information on the 5th Italian-Japanese Workshop on Liquid Crystals (IJLC 2010) that was held at the Grand Hotel San Michelle in Cetraro, Italy, on July 6-9, 2011. This workshop is a biannual meeting held between the two countries. The workshop was organised by the Licryl group in the University of Calabria. The opening address for the workshop was given by Roberto Bartolino from the University of Calabria.

We demonstrate polarization-independent refractive index modulation using an azo-dye doped liquid crystal (azo-LC). The azo-LC is aligned homeotropically and irradiated by ultraviolet (UV) light resulting in optically induced nematic-isotropic phase transition. This homeotropic-isotropic transition causes a refractive index modulation, which is independent of polarization for light travelling perpendicularly to the azo-LC layer. In order to evaluate the amount of the modulation, we fabricated an etalon which contains a homeotropically aligned azo-LC layer between the mirrors, and observed the polarization-independent refractive index modulation by 0.03. [ABSTRACT FROM AUTHOR]

Alignment characteristics of nematic liquid crystals on micro-scale grating structures fabricated by direct laser writing employing two photon excitation has been investigated upon changing periods and heights of the grating. Liquid crystal was infiltrated in the cell made of a substrate with gratings and another glass substrate with polyimide rubbed in the direction almost parallel to the grating vector of the structure in order to realize a twisted nematic configuration. Anchoring energies of the gratings were evaluated using the torque balance method, and were confirmed to be proportional to the height and inversely to the period of the grating. While the anchoring energy of the gratings turned out to be weaker compared to substrates treated by the conventional rubbing method, varying periods and heights of the grating allowed control of the anchoring energy. [ABSTRACT FROM AUTHOR]

The authors report continue tuning of the lasing wavelength in cholesteric liquid crystals (ChLCs) by an applied electrical fields. Although the pitch length and the corresponding lasing wavelength is sensible to external fields, only a discrete shift in the pitch is observed in the conventional cell configuration where the helix axis is lying the cell-normal direction, since the molecules are anchored to a single direction at the substrate interfaces. In this study, continuous wavelength tuning is achieved by laying the helix in the cell-plane direction, mitigating the effects of anchoring: this alignment is attained simply by applying an electric field while cooling the sample from the isotropic state, in a planarly rubbed sandwich cell. We also show that the tuning characteristics as that predicted based on calculations using the elastic theory. [ABSTRACT FROM AUTHOR]

Planar alignment of columnar liquid crystals was achieved in microgroove structures fabricated by a direct laser lithography using two photon polymerization. A liquid crystalline material exhibiting the columnar phase was sandwiched between a substrate with microgrooves and an untreated glass substrate, and the orientation characteristics were investigated with a polarizing optical microscope. A uniform uniaxial alignment was observed in the microgrooves, and the measurement of the optical birefringence indicated that the columnar director aligned perpendicularly to the grooves. [ABSTRACT FROM AUTHOR]

The authors numerically investigate the optical transmission properties of cholesteric liquid crystals with a local modulation of pitch and refractive indices. The transmittance spectra of structures with various defect thickness, refractive indices and pitch are calculated using the 4 × 4 matrix method. Calculation results showed that single or multiple transmittance peaks arise in the selective reflection band for light incidence with the same circular handedness as the material, and their spectral positions depend strongly on the physical parameter of the defect. A pitch shortening or elongation at the defect causes the defect mode to shift in the shorter or longer wavelength region, respectively, and the tuning range of the defect mode becomes larger for a thicker defect. We also show that efficient tuning is achieved by a defect medium with a smaller birefringence, allowing the defect mode to be sweeped through the photonic band gap with a smaller modulation of pitch. [ABSTRACT FROM AUTHOR]

The authors model a cholesteric liquid crystal material in which periodic elongation or shortening of the pitch has been introduced, and investigate its optical properties by the plane wave expansion method. The calculated photonic band structure revealed a continuous shift of the selective reflection band depending on the sign and degree of the modulation in pitch introduced. Anomalous selective reflection band-gaps were also observed at frequencies higher and lower than the original band-gap of the unmodified cholesteric liquid crystal, due to the longer periodicity experienced by the light interacting with the material. [ABSTRACT FROM AUTHOR]

The refractive indices of free-standing films (FSFs) of an antiferroelectric liquid crystal MHPOBC and a conventional smectic liquid crystal 8CB were studied by means of transmission and reflection ellipsometry. When the FSF thickness of MHPOBC is thicker than 260  nm, the refractive indices of FSFs appear to be the same as those of bulk smectic layers. In the case of thin FSFs of 8CB with a small numbers of layers, birefringence could not be obtained clearly by means of reflection ellipsometry. [ABSTRACT FROM AUTHOR]

Poly(propylene carbonate) which contains C 60 (OH) n structure in the end of polymer chain was synthesized by copolymerization of propylene oxide and CO 2 with Et 2 Zn-C 60 (OH) n catalytic system. Emission and absorption spectra of the product polymer were determined and discussed. An emission band with a few peaks in UV-region were seen in the emission spectrum. [ABSTRACT FROM AUTHOR]

We prepared a highly oriented thin film of the simplest polysilane, poly(dimethylsilylene) (PDMS) by friction transfer method. It had an ability of aligning liquid crystals. A liquid crystal, 4-cyano-4'- n -pentylbiphenyl (5CB) sandwiched between oriented PDMS layers was uniformly oriented. The molecular axis of 5CB lay in parallel to the direction of PDMS chains. PDMS films could be easily photooxidized by UV light irradiation. 5CB between UV-irradiated PDMS oriented in the different manner from that between non-irradiated PDMS. The PDMS orienting films could be patterned by irradiation with a shadow mask and the orientation of 5CB induced by them was patterned. [ABSTRACT FROM AUTHOR]

Molecular dynamics (MD) simulation was carried out for an antiferroelectric liquid crystalline molecule, (S)-4-[(1-methylheptyloxycarbonyl]phenyl 4′-octyloxybiphenyl-4′-carboxylate (MHPOBC), to analyze its conformational property in smectic liquid crystalline phases. The MD simulation reproduces a "solid-SmC x -SmA-isotropic" phase transition. The MHPOBC molecules in the SmC x phase are packed in a tilted layered structure, while in the SmA phase the molecular tilt disappears. The chiral alkyl chain in the crystalline phase has a larger gauche population at the C*-C bond, which gives rise to a "highly bent structure". In smectic phases, the conformation of both chiral and achiral alkyl chains is almost fully liberated, and the average molecular shape changes into a "moderately bent structure". Comparison of the results of MD simulation and molecular orbital calculation indicates that the smectic phases of MHPOBC can be distinguished from the solid phase in terms of the alkyl chain conformation, and the SmC x and SmA phases are distinguished from each other in terms of molecular packing structure. [ABSTRACT FROM AUTHOR]

The structure and dynamics in an optically isotropic liquid crystalline phase exhibited in a dichiral compound with fluorines have been investigated using X-ray, 19 F-NMR and dielectric measurements. Results in the dielectric measurement and 19 F-NMR measurements clearly show that molecular motion in this phase is just like in the isotropic phase as observed by texture. However, several X-ray diffraction peaks observed in a small angle range indicate akind of cubic phase (Cub). Based on the X-ray diffraction patterns together with the existence of circular dichroism, the phase is assigned to a chiral cubic structure belonging to crystallographic spacegroupI432. Moreover, the exotic phase with blue colored and foggy texture was found in the lower temperature range of isotropic liquid. X-ray diffraction in this phase clearly shows a diffraction ring corresponding to a layer structure, indicating that this blue-colored phase is assignable to a smectic blue phase (BP sm ). It was also found that the layer correlation length is remarkably long compared with the previously reported BP sm phases. We want to emphasize that the present material is quite unique in the sense that both cubic phases, BP sm and Cub, appear. The influence of cell thickness and incubation time on the emergence of the smectic C* phase is also discussed based on dielectric measurements and AC calorimetry. [ABSTRACT FROM AUTHOR]