Masato Isogai

New Room-Temperature Ferroelectric Liquid Crystals : Material Constants and Electro-Optic Properties

A binary ferroelectric liquid-crystal mixture having both room-temperature ferroelectricity and a large spontaneous polarization has been developed. The temperature range is from 20°C to 34°C. The spontaneous polarization is almost the same value, 4 nC/cm2, as that in DOBAMBC. Five material constants for the mixture; the transition temperature, spontaneous polarization, helical pitch, tilt angle and birefringence, are reported. A guest-host-type device was fabricated using the mixture, and some potential problems in the application of the materials to electro-optical switching devices are pointed out on the basis of the optical properties of this device.

Ferroelectric liquid crystal materials applied to guest-host type displays

Abstract Bistable ferroelectric liquid crystals (FLCs) suited for guest-host devices are described. Tilt angles of eight compounds and contrast ratios of the guest-host cells were measured as a function of temperature. The eight compounds were categorized into two classes. The first class exhibited the smectic A (SA) phase with a tilt angle of around 22°. The second class did not show the SA phase; the tilt angle was about 35° and almost constant over the temperature range of the smectic C(SC) phase. It was experimentally confirmed that the guest-host cell for the compound with the large tilt angle of 35° had a higher contrast ratio than 10. By using a binary system consisting of one compound from each class, influence of the tilt angle on bistability was examined. Increasing of the tilt angle improved not only the optical contrast ratio but also bistability.

X-ray studies on layer structure and bistability in ferroelectric liquid crystals

Abstract X-ray diffraction measurements of thin chiral smectic C (Sc∗) liquid crystals between solid plates coated with rubbed polymer film were performed under an electric field. A variety of local layer structures which depend upon the boundary conditions could be observed, including bookshelf and chevron, and some distorted structures. Moreover, the method of layer deformation could be seen in a stepwise induced field, and seven deformation types could be detected. The relation between a bistability effect and the type of layer deformation was clarified and four deformation types were found favourable to bistability. A vertical layer structure at the boundary, like the bookshelf structure, was necessary to produce bistability. A high pretilt film seemed to have a smectic layer reform a tilted structure even under an induced field and it was difficult to produce bistability with the high pretilt one.

Electrooptical Switching of Ferroelectric Liquid Crystals in Electrically Distorted Chevron Structure

Abstract X-ray diffraction studies on the field induced distortion of the layer structure in ferroelectric liquid crystals are reported. Depending on the liquid crystal materials and alignment layers, electric fields produced reversible or irreversible distortions. Bistable electrooptical switching was observed only in the samples with the irreversibly distorted layer structure. Experimental results on the light transmissions indicated that a bookshelf-like structure was formed in the above bistable sample. It seemed that this structure formation was essential to the bistability of the ferroelectric liquid crystals.

Molecular Design for New Second-Order Nonlinear Optical Materials

Abstract A molecular design method of second-order nonlinear optical materials for SHG device applications of diode lasers is proposed. The method consists of a semi-empirical MO calculation (CNDO/S3-CI) to evaluate molecular nonlinear optical properties of a molecule and an intermolecular interaction energy calculation to evaluate its crystallization property, in particular whether it crystallizes in a centrosymmetric structure or not. Using this method we design novel second-order nonlinear optical materials for our target applications: xanthone and benzophenone derivatives which have relatively large optical nonlinearity and short absorption cut-off wavelength.

Experimental Evaluation of Surface Tension Criteria for Alignment Behavior of Liquid Crystals on Solid Surfaces

Experimental verification has been carried out the surface tension difference criteria for liquid crystal alignment on solid surfaces. Organic polymer films, with surface tension values controlled from 16.0 to 44.8 mN/m (which includes the surface tension of liquid crystal ZLI-1132) were examined. On films thick enough to avoid undesirable topological effects ( >80 nm), the surface tension value at which the surface changed from a homogeneous to a homeotropic alignment was 31.2 mN/m, which is very close to the 31±0.5 mN/m value of ZLI-1132.

Synthesis and Some Properties of Low Melting Ferroelectric Liquid Crystals of Benzylidene Anilines

Abstract A series of chiral benzylidene-aniline compounds, 4-alkoxybenzylidene 4′-(2-methylbutyloxycarbonyl)anilines, have been synthesized and their mesomorphic properties are examined. They showed a monotropic chiral smectic C phase in conjunction with enantiotropic smectic A phase, and their chiral smectic C—smectic A phase transition temperatures are around room temperatures. Their spontaneous polarization values are moderately higher than those of DOBAMBC “4-decyloxybenzylidene 4′-amino-(2-methylbutyl)cinnamate”.

Numerical Analysis Method for Orientation Structures of Surface-Stabilized Ferroelectric Liquid Crystals

A computer simulation method for analyzing the dynamic orientation structures of surface-stabilized ferroelectric liquid crystals is presented. This method is based on a free-energy theory in which electrostatic, elastic distortion and surface interaction energies are taken into account. Some results of one-dimensional simulations which analyzed the relationships between the threshold of an applied electric field, material constants, bounding surface conditions and cell thickness are also presented and compared to theoretical considerations.

Second-order nonlinear optical properties and polymorphism of benzophenone derivatives

Abstract Some di-substituted benzophenone derivatives were found which have large nonlinear optical susceptibilities and short cut-off wavelengths of about 400 nm. The second harmonic generation (SHG) activity of 4-methoxy-4′-nitrobenzophenone, which was relatively suitable for a frequency doubler among benzophenone recrystallization rate. The difference in SHG activity was attributed to polymorphism, based on results of X-ray analysis and differential scanning calorimetry.

Theoretical Calculation of Nonlinear Optical Susceptibilities

Abstract A theoretical calculation method of nonlinear optical susceptibilities of organic materials is reported. The method consists of semi-empirical (CNDO/S3-CI) and ab initio molecular orbital calculations to evaluate molecular hyperpolarizabilities and a crystal energy calculation to evaluate the crystallization property. In the hyperpolarizabilities calculation, the semi-empirical molecular orbital (MO) calculation is applied to the study of second harmonic generation (SHG) materials, and a suitable chemical structure is described. The ab initio MO calculation for hyperpolarizabilities is performed and basis set dependence of the hyperpolarizability values calculated by a time independent perturbation method and a coupled-perturbed Hartree-Fock method is investigated. A space group limiting calculation for crystal energy of second order nonlinear materials by the accelerating convergence method is described. The calculated structures agree well with the experimental data.