Hirofumi Wakemoto

The effect of rubbed polymer films on the liquid crystal alignment

Abstract The observation of surface profiles on rubbed polymer films demonstrated that micro-grooves had been formed on the polymer surface. on the other hand, the infrared (I.R.) and U.V.-visible dichroic measurements of the rubbed polymer films have revealed that the polymer backbone chains are oriented parallel with the rubbing direction. We determined whether micro-grooves or polymer chain orientation causes the alignment of liquid crystal (LC) molecules. It was found in polystyrene (PS) films that LC molecules aligned perpendicular to the rubbing direction, although there were micro-grooves whose direction was the same as a rubbing direction. It was also found that the rubbed polyimide (PI) films lost LC alignment ability when they had been covered with Pt-Pd films about 30 A thick, even though micro-grooves were still present. The experimental results imply that LC molecules are aligned by the effect of the orientation of the polymer chains on a rubbed polymer surface.

48.4: Invited Paper: Fast Response OCB-LCD for TV Applications

OCB-LCD has fast response characteristics. In particular, the response time toward black state is less than 1 msec. It enables us to insert a black period between continuous two frames to make “pseudo-impulse” response on LCD. Subjective evaluation is carried out to clarify the effect of the black period. Viewing angle characteristics are also investigated.

Electrophotographic and structural studies on novel photoconductive polyimide films

Novel photoconductive polyimides have been developed, whose monomer units are composed of a series of thiophenylene moieties, ‐C6H4S‐, and imide groups. The most photosensitive polyimide shows an excellent photosensitivity of less than 1.0 μJ/cm2 in the visible light region, 400–570 nm. These photosensitive polyimide films are prepared by polymerizing the cast prepolymer films and annealing at the melting points of the polyimides. In this process their photosensitivities remarkably increase with the increase of crystallinity. From the structural studies by ultraviolet visible absorption, x‐ray diffraction, infrared absorption, and x‐ray photoelectron spectroscopy measurements, it is proposed that the coplanary conformation takes place in the crystallizing. The overlapped π orbitals, perpendicular to the polymer chains, lead to the more expanded conjugate system.

Polystyrene Derivative Films for Liquid Crystal Alignment

Abstract We studied the alignment of liquid crystal molecules on rubbed, thin polymer films of polystrene and its derivatives. Liquid crystal molecules were aligned perpendicular to the rubbing direction, although the polymer main chains of rubbed films were oriented along the rubbing direction. The alignment of the liquid crystal depended on the choice of side phenyl groups of polystyrene derivatives, and the pretilt angle varied with the type and the position of the substituents that were introduced into the side phenyl groups. Homogeneous alignment for ferroelectric liquid crystal was obtained by using poly(NO2 styrene), poly(p-OH styrene) and poly(4-vinylpyridine) films, which have relatively high β-dispersion and glass transition temperatures.

Synthesis ofN,N′-diacylindigotins (N,N′-diacyl-2,2′-bi-indolinylidene-3,3′-diones)via an oxidative oxygen-to-nitrogen acyl shift of O,O′-diacyl-leucoindigos(3,3′-diacyloxy-2,2′-bi-indolyls)

O,O′-Diacyl-leucoindigos (3f–j), which were readily obtained by the reaction of leucoindigo disodium salt (4) with acyl chlorides, underwent rapid oxidation by 2,3-dichloro-5,6-dicyanobenzoquinone (DDQ) to generate the indigo chromophore with concomitant shift of the acyl groups intramolecularly from oxygen to nitrogen. A number of N,N′-diacylindigotins with functionalized acyl groups were prepared by this method [(2a), (2f–j)] and the direct N-acylation method [(2a–e)]. A large bathochromic shift of the visible absorption band in the cis form of N,N′-diacylindigotins with bulky acyl groups (2c), (2d), and (2j) was observed which suggested that the electronic structure of the indigo chromophore is perturbed by the steric constraint of the N-acyl groups.

Photoconductive properties of a dye dispersed (oligo phenylene sulfide)‐polyimide

A dye dispersed photoconductor has been developed using (oligo phenylene sulfide)‐polyimide (OPS‐PI) as a matrix polymer. The OPS‐PI was comprised of a series of thiophenylene moieties, –C6H4S–, and imide rings, having a novel carrier transport ability. The dispersed photoconductor showed a panchromatic photosensitivity in the wide wavelength 400–900 nm region, which resulted from the carrier generation of the OPS‐PI in the wavelength 400–600 nm region and from that of the dyes, metal‐free phthalocyanines, in the wavelength 600–900 nm region. A model of sensitizing the OPS‐PI by means of dye dispersion is presented based both on the electronic structural study of the crystalline OPS‐PI and on the optical and photoconductive studies of the copolymers derived from the OPS‐PI and its modified polyimide. According to our proposed model, the optimum of the dye content in the OPS‐PI for enhancing photosensitivity has been determined in the range not to destroy the carrier transport paths.

Molecular Orientation and Anisotropic Photoconduction of Evaporated Oligo-p-Phenylene Sulfide Films

Thin films of highly oriented oligo-p-phenylene sulfide (OPS) molecules have been prepared by vapor deposition. This proves that the chain axis of OPS molecules has a directional arrangement perpendicular to the substrate with a decrease in deposition rate. Parallel OPS molecules, which are uniaxially oriented along the rubbing direction of a substrate covered with a rubbed polymer thin film, can be obtained by evaporation with a higher deposition rate. Photocurrent measurements of uniaxially oriented films along the rubbing direction have indicated that OPS molecules are anisotropic in photoconduction, that is, carriers are more easily transported perpendicular to the molecular chain axis than along that axis.

Synthesis and cis-to-trans isomerization of N,N′-diacyl derivatives of indigotin

The oxidative rearrangement of O,O′-diacyl derivatives of leucoindigo with dichlorodicyanobenzoquinone in dimethyl sulphoxide affords N,N′-diacyl derivatives of indigotin in high yield; it has been found that the heat of cis-to-trans isomerization in acetonitrile for N,N′-bis (phenylacetyl) indigotin is 29.9 kcal mol–1(60 cal g–1).

A 23-in. UXGA-wide advanced IPS TFT-LCD with new driving method

Abstract A new 23-in. diagonal in-plane-switching (IPS) mode TFT-LCD with H1920×V1200 pixels has been developed. This TFT-LCD, which is a new structure with zigzag shaped pixels, has been adopted as an advanced IPS technology. Using this structure, the aperture ratio becomes 25% larger than that of conventional liquid crystal displays (LCDs). Furthermore, uniform image quality has been obtained by using the new dual-line driving method where the design has optimized storage-capacitance for each pixel.

Anisotropic photoconduction in novel photoconductive (oligo phenylene sulfide)–polyimide films cast on a Langmuir–Blodgett polyimide underlayer

Two methods for preparing highly oriented crystalline polyimide films comprised of oligo‐p‐phenylene sulfide [–(C6H5S)n−1–C6H4–:n=3,4,5...] monomers have been developed, which show novel photoconductivity. The first method is using modified terminals of the polymer chains for carboxylic anhydrides as crystallization nuclei in order to enhance the crystallization of the (oligo phenylene sulfide)–polyimides (OPS‐PIs). The second uses a Langmuir–Blodgett polyimide underlayer to prepare oriented OPS‐PI films parallel to the substrate, extending up to several microns. The Langmuir–Blodgett polyimide underlayer introduces an oriented epitaxial crystallization of the OPS‐PIs. Anisotropic photocurrent measurements on these films revealed an anisotropic photoconduction mechanism in which carriers were transported perpendicular to the polymer chain axis.