Jürg Fünfschilling

Deformed helix ferroelectric liquid crystal display: A new electrooptic mode in ferroelectric chiral smectic C liquid crystals

Abstract A new electrooptic mode of operation of ferroelectric chiral smectic C liquid crystal displays (LCDs) is proposed and demonstrated. The effect, which is called the deformed helical ferroelectric (DHF) effect, is based on the deformation of the helical structure by weak electric fields. In the unbiased device the smectic layers are arranged in the bookshelf geometry with the helix axis parallel to the electrodes [1]. Systems with a very small pitch (<1 μm) and a large tilt angle are especially well suited for this mode. The key characteristics of DHF-LCDs are: (a) low driving fields (1 Vp-pμm−1 for maximum contrast); (b) grey scale which is approximately linear with the applied electric field; (c) easy alignment even for thick cells using standard wall-aligning methods; and (d) response times at room temperature of 300 μs.

New Short-Pitch Bistable Ferroelectric (SBF) Liquid Crystal Displays

We present a new type of bistable electro-optical device based on ferroelectric Sc* liquid crystals exhibiting a short pitch (0.43 µm) and a large spontaneous polarization (50150 nC/cm2). Features of the new short pitch bistable ferroelectric liquid crystal displays (SBF-LCDs) which are based on the effect are: short switching times (25 µs) at room temperature using 2 µm cell gap and 30 V bipolar pulses; contrast ratios>35; multiplexing ratios>1000; large on-state brightness due to a large memory switching angle of 40° as well as a weak temperature dependence of both, response time and memory tilt angle.

New Liquid Crystal Polarized Color Projection Principle

A wide-aperture, color projection principle is presented whose functional parts, namely, polarizers, bandpass filters and electrooptical modulators, consist entirely of liquid crystal elements. The concept ideally enables one hundred percent input-output light conversion. The angular and wavelength dependences of planar cholesteric layers and layer combinations are shown. From them optical filter/polarizer elements result with adjustable center wavelengths and tunable bandwidths. The filters comprise novel cholesteric liquid crystals with a temperature dependence of their center wavelengths as low as 0.06 nm/°C. New, circularly polarized operating modes for twisted nematic (TN-LCDs) and other field effects exhibit not only low threshold voltages, but also voltage-transmission (reflection) characteristics whose slope is adjustable over a wide range. Thus, the new modes are applicable in high-information-content, actively addressed television TN-LCDs requiring gray scale, as well as in displays requiring large time multiplexing rates approaching those of supertwist LCDs.

Strongly non-linear optical ferroelectric liquid crystals for frequency doubling

Abstract From our research for novel non-linear optical (NLO) materials for frequency doublers and optical modulators we report on new ferroelectric liquid crystals, which for the first time, exhibit second order NLO coefficients (for example d 22 = 5 pm V−1, which are comparable to those of state of the art inorganic NLO materials. The novel compounds contain 5-amino-2-nitrophenyl groups attached close to the chiral centres. The switching behaviour of the new compounds, their spontaneous polarization, as well as their frequency doubling of Nd:YAG laser pulses in the S*c and in the glass state, are reported. Moreover their waveguiding properties are presented.

Large Aperture Polarized Light Source and Novel Liquid Crystal Display Operating Modes

A wide aperture liquid crystal polarized light source (LC-PLS) is presented which converts unpolarized-into circular- and/or linearly polarized light with an efficiency better than 80%. Moreover, new operating modes for electro-optical field-effects on which liquid crystal displays (LCDs) are based are shown to increase the transmission of twisted nematic (TN)-LCDs by a factor of two. Besides, a 25% shift of the TN-LCD transmission-voltage characteristics towards lower voltages is achieved. One of the new, reflective LCD-operating modes is shown to avoid light absorption by thin film transistor structures in actively addressed LCD-projection systems. Within the bandpass region of the cholesteric liquid crystal filters the combination of LC-PLS with appropriate LCD-operating mode is shown to increase the transmission of LCD-projection systems three to five times compared with conventional LCD-projectors.

Performance of Conventional and Novel Deformed Helix Ferroelectric Liquid Crystal Display Operating Modes

Fast response times and wide viewing angles are characteristic features of the deformed-helix ferroelectric liquid crystal displays (DHF-LCDs) presented in this paper. We first discuss the electrooptics of the DHF effect, emphasizing the large electrically induced changes of birefringence which occur in DHF-LCDs with large switching angles. Based on these results a new DHF operating mode is introduced, which allows DHF display cell gaps larger than 5 µm. A second new type of DHF-LCD operating mode is then presented, which is used for low-tilt-angle DHF materials. This second, double-layer DHF-LCD allows fast, bright, ghost-free, low-voltage operation. Finally, the influence of various FLC material parameters and their temperature dependence on DHF display performance is investigated. It is shown that a pitch below 150 nm at room temperature is required for high-contrast DHF-LCDs. It is also shown that with suitable driving electronics, operation of DHF-LCDs at video rates is possible down to -15°C.

Smectic C phenylpyridines with an alkenyloxy chain

Abstract The known 5-n-alkoxy-2-[4-(n-alkoxy)phenyl]pyridines exhibit high smectic C transition temperatures as well as various highly ordered smectic mesophases. An unsaturated carbon-carbon double bond has now been introduced into the terminal alkoxy chain of these heterocyclic materials to produce the corresponding alkenyloxy substituted derivatives. The postion and nature (E/Z) of the double bond has been varied systematically and the effect on the liquid crystal transition temperatures determined. A number of homologous series of the most promising alkenyloxy substituted materials has been prepared and evaluated. The position and nature (E/Z) of the double bond changes the conformation of the alkenyloxy chain to a significant degree. This can lead to slightly higher smectic C transition temperatures for compounds with a trans-double bond (E) at an even number of carbon atoms from the molecular core. However, the highly ordered mesophase transition temperatures are increased to a greater degree leadin...

Four unit linking groups II. Some novel smectic C materials

Abstract About 40 diverse phenyl benzoate esters incorporating a trans-1-4-disubstituted cyclohexane ring joined to the central aromatic core by new four unit linking groups (C4H8, C4H6, C3H6O and C3H4O) have been synthesized. The effect of various lateral substituents (F, Cl, CN and Br) and especially two fluorine atoms in the 2,3-positions of the 4-n-alkoxybenzoate part of the esters has been investigated. Three homologous series of 5-n-alkyl-2-(4-phenyl)pyrimidines incorporating the same four unit linking groups have also been prepared. Many members of the ester and pyrimidine series exhibit enantiotropic smectic C mesophases at moderately elevated temperatures. Several esters and pyrimidines have been found to improve the surface alignment and temperature range of chiral smectic C mixtures for surface stabilized ferroelectric liquid crystal displays. The effect of the new four unit linking groups on the liquid crystal transition temperatures, rotational viscosity and spontaneous polarization of their ...

The influence of double bonds in the terminal chain of 2-ring compounds on the physical properties of S*c mixtures

Abstract We present the properties of S*c mixtures containing new 2-ring 5-n-alkyl-2-(4-n-alkenyloxyphenyl)pyridines and pyrimidines with systematically varying positions and configurations of the double bond Trans configurations at odd positions (counting the number of atoms from the core including the oxygen and the first carbon atom of the double bond) suppress the SA phase, increase the S*c tilt angle, Θ, and the spontaneous polarization, P s, and lead to long switching times τ. Cis configurations at even positions suppress the nematic phase in favour of smectic phases, decrease Θ and P s, and shorten τ. Other positional configurational combinations strongly reduce the clearing point. Furthermore, our results indicate that the preferred conformation of the alkenyloxy chain consists of alternating cis and trans units.

2-(4-Alkylphenyl)-5-(alkenyloxy)pyrimidines: Synthesis, liquid crystal transition temperatures and some physical properties

Abstract We have recently reported the introduction of a carbon-carbon double bond into a wide variety of 5-n-alkyl-2-(4-n-alkoxyphenyl)pyrimidines to produce the corresponding alkenyloxy derivatives. The position and nature (E/Z) of the double bond were varied systematically and the effect on the liquid crystal transition temperatures studied. The position and nature (E/Z) of the double bond changed the conformation of the alkenyloxy chain substantially. This resulted in higher smectic C and nematic transition temperatures for compounds with a trans-double bond (E) at an even number of carbon atoms from the molecular core. Significantly lower transition temperatures (including the melting point) were observed for materials with a cis-double bond (Z) at an odd number of carbon atoms from the molecular core. We have now performed the same operation on the related 2-(4-n-alkylphenyl)-5-n-alkoxypyrimidines to produce the corresponding alkenyloxy derivatives. An interesting feature of the new results is the h...