Lateral Fluoro Substituents Research Articles

Cyclohexenyl triflates and arylboronic acids in palladium-catalysed cross-couplings. Synthesis and transition temperatures of some fluoro-substituted biphenylylcyclohexenes

A range of liquid crystalline materials with low melting points have been prepared that incorporate a cyclohexene ring in the core. Substituted cyclohexanones were converted into their vinyl triflate derivatives by generation of the lithium enolates using LDA and subsequent quenching with N-phenyltriflamide. The vinyl triflates were then coupled to a range of fluoro-substituted arylboronic acids (generated using ortho-directed metallation techniques at low temperature) in a novel reaction to provide liquid crystals with very low melting points. The lateral fluoro-substituents play an important role in modifying the mesomorphic and physical properties of the materials; the effects of the position of fluoro substitution on the mesomorphic behaviour is discussed.

ChemInform Abstract: Effect of the Position of Lateral Fluoro Substituents on the Phase Behaviour and Ferroelectric Properties of Chiral 1‐Methylheptyl 4′‐((2‐ or 3‐Fluoro‐4‐tetradecyloxyphenyl)propioloyloxy)biphenyl‐4‐ carboxylates.

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Effect of the position of lateral fluoro substituents on the phase behaviour and ferroelectric properties of chiral 1-methylheptyl 4′-[(2- or 3-fluoro-4-tetradecyloxyphenyl)propioloyloxy]biphenyl-4-carboxylates

The syntheses of four chiral laterally fluoro-substituted propiolate esters are described, along with transition temperatures, ferroelectric properties, phase diagrams and related data. The position of the fluoro-substituent was found to influence dramatically the formation of twist grain boundary (TGB A* and TGB C*) phases as well as the magnitudes of spontaneous polarization and optical tilt angle in the ferroelectric smectic C* mesophases. Differential scanning calorimetric studies revealed the presence of a diffuse liquid-liquid transition above the clearing point in both of the 3-fluoro enantiomers, but not in the racemate. Circular dichroism and optical rotation measurements, carried out over a temperature range in which the diffuse peak occurs, appear to confirm the presence of a degree of chiral organization within the isotropic liquid. It is suggested that this phenomenon may be due to the presence of cybotactic groups or a network of entangled screw dislocations occurring close to the clearing point.

Inversion of chirality-dependent properties in helical liquid crystals: effects of structural modification

The effects of structural modification on the inversion of chirality-dependent properties in the helical mesophases of a number of terphenyls have been investigated. The occurrence of inversion phenomena are very sensitive to small changes in the molecular structure and subtle changes can often produce profound effects. Structural modification of the non-chiral or chiral terminal chains has been shown to destabilize the inversion of chirality-dependent properties; however, a stable room temperature ferroelectric smectic C* phase has been prepared. The inclusion of lateral fluoro-substituents in the aromatic core causes a large reduction in the melting points of the terphenyl materials and the stabilization of inversion phenomena in the cholesteric phase. Changes in the fluoro-substitution pattern results in a change in the direction of the molecular dipole and hence a change in the sign of the spontaneous polarization. Helical mesophases and therefore also inversion phenomena are suppressed in the non-fluorinated material.

Laterally fluorinated tolanes of low melting point

Abstract Tolanes having a terminal polar group and a lateral fluoro substituent are reported with the desirable features of high birefringence, wide nematic range and low melting point.

Lateral fluoro substituted 4-alkyl-4″-chloro-1,1′:4′,1″-terphenyls and derivatives. Useful high birefringence, high stability liquid crystals

Abstract By modification of the basic 4-alkyl-4″-chloro-1,1′:4′,1″-terphenyl structure with lateral fluoro substituents and ethyl linking groups, a wide range of mesogens has been synthesized. Control over the phase behaviour, especially optimization of nematic properties, can be achieved by the degree and position of lateral fluoro substitution and/or the presence and position of an ethyl linking group. The effect of these changes on the physical properties such as dielectric anisotropy (Δε) and birefringence (Δn) has also been studied. Compounds of low melting point, wide nematic range and high birefringence (>0·2) have been made. These materials are suitable for active matrix display applications where high chemical and photostability are necessary.

New ferroelectric liquid crystal having 2-methylalkanoyl group

Abstract A relationship between molecular structure and physical properties of newly prepared ferroelectric liquid crystals having 2-methylalkanoyl group is investigated by observing the phase transition temperatures, the spontaneous polarization, and the bistability. Carbon chain length is proved to play an important role not only in the thermal stability of the SC phase but also in the magnitude of the spontaneous polarization in this phase. A lateral fluoro substituent is efficient at producing more stable SC* phase and reducing the occurrence of higher ordered phases. Especially the lateral fluoro substitution at the ortho position to the chiral tail favors the uniform state and contributes to the bistability.