Sung-Tae Shin

Electro-optic characteristics and switching principle of a single-cell-gap transflective liquid-crystal display associated with in-plane rotation of liquid crystal driven by a fringe-field

A single-gap transflective liquid-crystal (LC) display associated with in-plane rotation of the LC director was designed. In the device, a fringe electric field drives to rotate a homogeneously aligned LC in plane to optimize polarization efficiency. Rotating degrees of the LC director, 22.5° and 45° were required in both reflective and transmissive regions, respectively. In the device, the cell gap was the same for both regions, and a dark state was irrespective of the cell retardation value at normal direction, which was highly important in massive fabrications. The switching principle and electro-optic characteristics of the device are reported herein.

Synthesis and properties of new liquid crystalline compounds containing an indolinobenzospiropyranylazo group. Part 3

Abstract Two series of liquid crystalline dyes (series 1 and 2) containing novel mesogens incorporating a non-activated spiropyranylazo group have been synthesized. Those mesogens are derived from [1′,3′,3′-trimethylspiro(2H-1-benzopyran-2,2′-indoline)-6-yl] azobenzoic acid and 6-(p-hydroxyphenylazo)-1′,3′,3′-trimethylspiro[2H-1-benzopyran-2,2′-indoline] for the series 1 and 2, respectively. Their liquid crystalline properties were studied by differential scanning calorimetry, optical polarizing microscopy and electro-optical measurement. Most of the compounds in series 1 form the enantiotropic nematic phase, while compounds in series 2 form the monotropic nematic and SmA phase.

Synthesis and properties of new materials with banana-shaped achiral cores and chiral end groups

New chiral bent-core mesogens, derivatives of 1,3-phenylene bis[4-(alkanyloxyphenyliminomethyl)benzoate], were synthesized with variation of a substituent (X=F, Cl); their antiferroelectric properties are described. The mesomorphic and switching properties were characterized by differential scanning calorimetry, polarizing optical microscopy, triangular wave method, and X-ray diffractometry in the small and wide angle regions. The presence of chiral tails at the terminals of side wings in the bent-core molecules induced a decrease in transition temperature and formation of the switchable SmC* phase in the melt. In addition, the introduction of a lateral halogen substituent in the Schiffs base moiety prevented the regular stacking of the molecules, resulting in the formation of very complex optical textures. The smectic phase with F-substituted PBFDOB and Cl-substituted PBCDOB showed layer spacings of 39 and 38.5 Å, respectively, corresponding to the end-to-end distance of molecules with a bent conformation. Significantly, the smectic phases of PBFDOB and PBCDOB exhibited a period of 179.5 and 131 Å, respectively, compatible with a helical structure with periodicity about 4.6 and 3.4 times the layer spacings.

Mesomorphic properties of achiral halogen-substituted banana-shaped compounds

Three banana-shaped achiral compounds, derivatives of 4,6-dichloro-1,3-phenylene bis-[4-(4-n-octyloxyphenyliminomethyl) benzoate], were synthesized by varying the substituent (X = H, F and Cl). Their mesomorphic properties were investigated by differential scanning calorimetry, polarizing optical microscopy, and X-ray analysis. The compound with X = H exhibited an enantiomeric nematic phase. The compounds with X = F and Cl formed a nematic phase on heating, while on cooling they formed a nematic phase at high temperature and a smectic A phase at a lower temperature (monotropic). A schematic representation of the mesophase structures for the compound with X = F is also illustrated.

Banana‐shaped molecules with 4,6‐dichlorinated central core: effect of lateral substituents and terminal chains on the formation of antiferroelectric smectic mesophases

Six banana‐shaped compounds with a central core based on a 4,6‐dichloro‐1,3‐phenylene group were synthesized by varying the terminal chains (R = OC10H21 or OC11H21) and the lateral substituents (X = H, F or Cl). Their mesophases were characterized by a combination of differential scanning calorimetry, polarizing optical microscopy, triangular wave method, and X‐ray diffractometry. Mesomorphic properties of the banana‐shaped mesogens with an olefinic group (R = OC11H21) as a terminal chain are sensitive to lateral halogen substituents as much as those of the analogues with a saturated group (R = OC10H21). The compounds with X = F showed an antiferroelectric switchable smectic phase, which has been designated a B2 phase. The compounds without a lateral halogen substituent only formed a nematic phase, while the compounds with X = Cl did not exhibit a mesophase in the melt.

Synthesis and mesomorphic properties of banana-shaped achiral molecules with central and lateral halogen substituents

Three banana-shaped achiral compounds, derivatives of 4-chloro-1,3-phenylene bis[4-(4-n-decanyloxyphenyliminomethyl)benzoate], were synthesized with variation of a substituent (X=H, F, or Cl); their antiferroelectric properties are described. The mesomorphic and switching properties were characterized by polarizing optical microscopy, differential scanning calorimetry, triangular wave method, and X-ray diffraction. The introduction of a lateral halogen substituent in the Schiffs base moiety prevents the regular stacking of the molecules, resulting in a decrease of melting temperature and leads to formation of the switchable SmC* phase in the melt. All of the compounds showed antiferroelectric switching, and their values of spontaneous polarization on reversal of an applied electric field were 260, 480, and 300 nC cm−2, respectively, for X=H, F and Cl.

Synthesis and characterization of new liquid crystalline materials containing a non-activated arylazoindolinobenzospiropyranyl group as a chiral unit. Part II

Two series of new liquid crystalline compounds containing a non-activated arylazoindolinobenzospiropyran, ABP-SPAB 1a-1e (series 1) and SPAP-ABPC 2a-2e (series 2), have been synthesized. These LC dyes were characterized by a differential scanning calorimetry polarizing optical microscopy, X-ray diffraction and electro-optical measurements. All but one of the series 1 compounds examined exhibit monotropic second and/or third transition liquid crystal phases on cooling from the isotropic liquid. In particular, ABP-SPAB 1b shows a monotropic SmC phase, in addition to a SmA phase. In series 2, most of the compounds exhibit a monotropic nematic phase on cooling. SPAP-ABPC 2c forms an enantiotropic nematic phase and a monotropic SmA phase; 2e shows enantiotropic nematic and SmA phases.

Pixel-Isolated Phase-Separated Composite Organic Film for Flexible Ferroelectric Liquid Crystal Display Applications

We have studied a pixel-isolated phase-separated composite organic film (PI-PSCOF). This PI-PSCOF is used for anisotropic phase separation from ferroelectric liquid crystals (FLCs) and prepolymer materials using an appropriate UV intensity variation. In this device, the FLC molecules are isolated in the pixels where FLCs are surrounded by the interpixel vertical polymer walls and the horizontal polymer films on the upper substrate. These devices show very short response time and very high mechanical durability against external pressure. We also compared the pure FLC, conventional phase-separated composite film (PSCOF) and PI-PSCOF mode in terms of their electrooptic characteristics and X-ray layer structure measurements. Compared with the PSCOF mode, PI-PSCOF exhibits good electrooptical behaviors. Consequently, we achieved an excellent device scheme suitable for flexible substrates, using the PI-PSCOF mode and expect that this PI-PSCOF scheme will be one of the powerful and promising new FLC display modes, particularly applicable to flexible FLC display modes.