Kundalika M. More

Ferroelectric properties of a series of core-fluorinated dopants containing the 2,3-difluoroalkoxy tail

Abstract Previous reports from these laboratories [1] have discussed the synthesis and properties of core-fluorinated phenylpyridines with an attached difluoroalkoxy tail. This paper discusses core-fluorinated phenylpyridine difluoroalkoxides and compares their properties to those of the corresponding phenylpyrimidines. The pyridine and pyrimidine series are found to be remarkably similar in properties. They have similar high polarizations and fast rise times, attractive in surfacestabilized ferroelectric liquid crystal (SSFLC) applications, and in high concentration have pitch properties compatible with deformable helix FLC applications.

Three-ring mesogens containing p-carboranes: characterization and comparison with the hydrocarbon analogs in the pure state and as additives to a ferroelectric mixture

A series of sixteen three-ring esters of carboxylic acids derived from p-carborane, bicyclo[2.2.2]octane and benzene were synthesized and their mesogenic properties investigated using polarizing microscopy and DSC. The stability of the nematic phases follows the order BCO > Ph > 12-vertex > 10-vertex (or C > D > A > B). The biphenol derivatives 1 and 2 show significantly more rich smectic behavior than the pyrimidinylphenol esters 3 and 4. Most of the esters show the expected effect on FLC properties of a host mixture. The exceptions are BCO derivatives 2C and 4C, which significantly lower the normalized Ps, and the carborane derivative 4A which significantly increased the normalized Ps and γs values. In contrast to the hydrocarbon analogs, carborane esters lower the tilt angle.

High-Tilt, High-PS, de Vries FLCs for Analog Electro-Optic Phase Modulation

Four new de Vries I-A-C* ferroelectric liquid crystal mixtures have been formulated to have high tilt (45°), high polarization, and low smectic layer shrinkage for use in analog electro-optic phase modulators. The mixtures are based on a high-tilt anti-ferroelectric compound which, when combined with other compounds, results in ferroelectric I-A-C* materials. Three of the mixtures include a new germanium-containing liquid crystal compound. X-ray diffraction measurements show layer contraction as small as 7%, while the temperature-dependence of birefringence shows a sharp increase at the A → C* transition as expected of a de Vries material. Charge control drive produced V-shaped switching with low hysteresis.

Tolane cinnamates—a new class of stable, high birefringence dopants

Abstract Ferroelectric smectic C* liquid crystals have been shown to exhibit high speed, electro-optic switching when incorporated into the surface stabilized ferroelectric liquid crystal (SSFLC) light valve. Certain applications utilizing IR modulation, waveguide, and phase modulation, and certain fiber-optic devices, can benefit from materials with a birefringence higher than that typically seen in FLC materials (Δ≊ 0.15). A new class of compounds, the tolane cinnamates, was developed to help meet this need. They were made by attaching a cinnamate moiety to the well known high birefringence tolane core. This resulted in two improvements: first, the birefringence increased from 0.23 to over 0.3; and second, the tolane cinnamate system was significantly more stable to UV light than the parent tolane system. The new materials showed smectic C as well as nematic phases and demonstrated good compatibility with both nematic and FLC hosts.

High performance electroclinic materials

Abstract Many interesting potential applications of the electroclinic effect continue to drive new materials development. Herein we present recent results of a project aimed at obtaining improved electroclinic materials.

Properties of a series of phenylpyrimidine ferroelectric liquid crystals possessing the 2,3-difluoroalkoxy tail

Abstract A series of high polarization Ferroelectric liquid crystal (FLC) dopants based on the 2,3-difluorohexyloxyphenylpyrimidine family was modified by 1) fluorination of the core and 2) replacement of the alkyl achiral tail with an alkoxy tail. Their polarization, rise time, N* and C* helical pitch, and effect on smectic A/C* phase transition as a 10% mixture in an achiral phenylpyrimidine host were determined. In all cases, core fluorination and alkoxy substitution results in a decrease in polarization while rise time remained relatively constant. All modifications resulted in a lengthening of the C* pitch relative to the parent structure. In several cases core fluorination resulted in sign reversal of the N* pitch making use of these dopants potentially useful as pitch compensating agents an attractive possibility.

Germanium liquid crystals

Liquid-crystalline compounds containing germanium atoms were synthesised and assessed for liquid-crystalline properties. These new compounds generally possess smectic C phases, and many also possess nematic, smectic A and higher order smectic phases. The germanium-containing liquid crystals were incorporated into smectic C mixtures. These mixtures tend to exhibit little change in smectic C*u2009layer thickness over temperature. This characteristic is associated with de Vries smectic A materials, but measurements show that, although they have high smectic C stability, the materials smectic cone angles are small. Measurement of smectic cone angle versus temperature of an exemplar material and its analogues containing carbon and silicon in place of the germanium, all show small cone angles which fall smoothly and extrapolate to zero as the smectic C*u2009to smectic A transition is approached. These measurements largely explain the observed small layer changes and establish that the materials are not first-order de Vries materials. They must be located elsewhere along the de Vries-orthogonal continuum of smectic A phases.

High resolution, color FLC miniature display and FLC materials optimized for their operation

Abstract We describe miniature (<1 cm2) 640 × 480 and 1280 × 1024 active matrix liquid crystal displays composed of a ferroelectric liquid crystal light-modulating layer placed on top of a reflective CMOS backplane and illuminated with red, green, and blue LEDs. The images are magnified for viewing. Truly miniature displays are difficult to produce with traditional display technologies. Such a display should be small and light enough to mount in a pair of eyeglasses or to incorporate in a pocket-size portable communications device. It should show bright, color images running at video-rate speeds with work-station resolution while operating for long periods on small batteries. The display should also be mass manufacturable at very low cost.

FLC materials for microdisplay applications

FLCs exhibit the electro-optic speed necessary for construction of full color, high resolution DRAM-based microdisplays. Special FLC materials are required to meet the performance characteristics required of these reflective microdisplays. The specifications for FLC mixtures for several applications, and an approach to formulating them, is presented herein.

New Chiral Dopants Based on the 2-Fluoro-2-Methylalkoxy Tail for Use in Ferroelectric Liquid Crystal Mixtures

Abstract A new class of FLC materials based on the 2-fluoro-2-methylalkoxy tail is reported. This new class of materials consistently shows an N* helical pitch opposite in sign to that of the polarization. These materials are compared to their 2-fluoroalkoxy analogs to explore the methyl groups effect on the N* pitch and polarization.