4-(5-Alkyl-2-pyridinyl)phenyl alkanoates: Some novel smectic materials for display devices

Abstract

Three homologous series of 4-(5-alkyl-2-pyridinyl)phenyl alkanoates have been prepared. The synthesis and the liquid crystal transition temperatures of these esters are reported. Many members of these three ester series exhibit enantiotropic, wide range smectic F mesophases and some narrow range smectic C mesophases. However, in admixture with a chiral smectic C base mixture, the esters often induce a substantial increase in the chiral smectic C–smectic A transition temperature and, at the same time, decrease the temperature of crystallization. Thus, the temperature range of the chiral smectic C mesophase is substantially extended at both high and low temperatures. Ordered smectic mesophases are only observed at very low temperatures, if at all. These chiral smectic C mixtures are characterized by short switching times in surface-stabilized ferroelectric liquid crystal displays (SSFLCD). These novel esters are of especial interest for short-pitch chiral smectic C mixtures for short pitch bistable ferroelectric liquid crystal displays (SBFLCD) with short response times.     

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 high melting points of the trans-substituted materials and the low melting points of the terminally substituted compounds. The smectic C transition temperatures of both series are high. No nematic phases could be observed. However, in admixture with other smectic C components, the new compounds lead to surprisingly fast switching times, high smectic C transition temperatures and low melting points/crystallization temperatures in experimental mixtures designed for electro-optic display devices based on ferroelectric effects.     

Novel 2-(4-octylphenyl)pyridin-5-yl alkanoates and alkenoates: Influence of dipoles and chain conformation on smectic C formation

A series of 2-(4-octylphenyl)pyridin-5-yl alkanoates has been synthesized and found to exhibit smectic mesomorphism including the smectic C phase. The influence on the transition temperatures of introducing a carbon-carbon double bond in the terminal alkanoyloxy (ester) chain of the alkanoates to produce the corresponding alkenoates has also been investigated. The position and configuration of the double bond has been changed systematically in order to determine the optimal configuration and conformation of the terminal chains for smectic C formation. The observed results are consistent with a linearly-extended (alternately cis and trans) conformation of the chain. The dependence of the transition temperatures on chain length was studied for one homologous series each of the alkanoates and the (E)-alk-2-enoates. The new esters are constitutional isomers of the 5-(4-octylphenyl)pyridin-2-yl alkanoates and alkenoates previously synthesized (differing only in the position of the nitrogen atom). Comparisons revealed consistently higher smectic C transition temperatures and lower ordered smectic tendencies for the new esters. The dependence of S_c formation on the position and number of dipoles associated with oxygen atoms, nitrogen atoms and carboxy groups was also investigated. Several of the new esters exhibit remarkably low viscosity values (i.e. short response times) in an optically active base mixture used for evaluation and comparison purposes.     

SITE-SELECTION SPECTROSCOPY OF CHLOROPHYLL b IN MEMBRANES OF LECITHIN VESICLES AND IN OTHER SOLVENTS

Abstract— Site-selection fluorescence spectra of chlorophyll b in membranes of lecithin vesicles and in the solvents ethanol, n -butanol, n -butyl acetate, 2-methyl tetrahydrofuran and toluene are presented. The spectra in vesicles display zero-phonon lines as pronounced as those in the best organic glasses. The characteristics of the distributions of O—O transition energies and of the electron-phonon couplings allow to infer the position of the chlorophyll molecule in the membrane of vesicles. It is thus found that the chromophore of chlorophyll b is situated in the layer formed by the ester moieties of the lecithins, i. e. close to the surface of the membrane but not in direct contact with the aqueous phase.     

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

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 high melting points of the trans-substituted materials and the low melting points of the terminally substituted compounds. The smectic C transition temperatures of both series are high. No nematic phases could be observed. However, in admixture with other smectic C components, the new compounds lead to surprisingly fast switching times, high smectic C transition temperatures and low melting points/crystallization temperatures in experimental mixtures designed for electro-optic display devices based on ferroelectric effects.     

Site selection spectroscopy luminescence of solutions with laser excitation

The narrow line emission observed by Personov et al. at low temperature in a glassy matrix from perylene has been shown to be observable from many other molecules. Spectra of 1-chloronaphthalene and tetracene are presented. Narrow line phosphorescence was not observed. Narrow line fluorescence was also absent when the excitation energy was 1500 cm^?1 greater than the 0–0 fluorescence level and in these two cases it is suggested that heating of the matrix by radiationless processes causes the spectral broadening.     

FLUORESCENCE SPECTRA OF CHLOROPHYLL-a AND CHLOROPHYLL-b FROM SITE SELECTION SPECTROSCOPY

Abstract— …Highly resolved fluorescence spectra of chlorophyll- a and - b have been measured in ethanol and methyltetrahydrofuran glasses at ˜4K. The vibrational frequencies measured are independent of solvent and were highly reproducible, ±1cm^-1 or less. A possible use of this experimental technique as an analytical tool is discussed.     

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 V_p-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.     

The temperature dependence of phosphorescence lines in glassy matrices

The temperature dependence from 1.8 to 4.2 K of The linewidth of phosphorescence site-selection spectra has been measured with a Fabry-Pérot interferometer. For coronene and 5-bromoacenaphthene in 1-bromobutane, the linewidth follows a T^1.25±0.2 power law. The lowest linewidth measured was 0.0012 cm^?1 for coronene at 1.8 K. Magnetic fields up to 0.32 T did not influence this width.