Sub-millisecond Switching and Ferroelectric-like Polarization in a Bent Shaped Liquid Crystal Exhibiting Nematic and Twist-bend Nematic Phases

A fast switching liquid crystal (LC), especially in its nematic (N) phase, can significantly improve the performance and properties of present-day electro-optic devices and displays. We investigated the polar nature and switching behaviour of a bent shaped liquid crystal (LC) CB7CB at different temperatures, subjected to applied voltages of varying amplitude and frequency. A threshold-dependent polarization current response, with large spontaneous polarization, was observed in the nematic (N) and in the twist-bend nematic (Ntb) phases exhibited by the LC compound. The current response was identified as ferroelectric-like in nature, and the corresponding switching time was found to lie in the range of ~ 500 {\mu}s in the N phase, which is fast compared to the usual nematic switching time (in the range of milliseconds). The nematic switching is bi-stable in nature and the nematic polarization arises from the collective reorientation of cybotactic clusters on field-reversal. At larger voltages, the twist-bend helices were observed to unwind which can be considered as the main reason for the polar response in Ntb phase. The fast, bi-stable switching nature exhibited by the compound may become useful for application in next-generation of electro-optic devices.Comment: 18 pages, 17 figures, 1 tabl

A first low-molar-mass, monodispersive, bent-rod dimer exhibiting biaxial nematic and smectic A phases

A "peelable banana" is formed when a bent-core molecule is linked to a rodlike mesogen through a flexible aliphatic spacer. This is an appropriate description of this novel low-molar-mass organic system, which displays a transition from a biaxial nematic (Nb) phase to a biaxial smectic A phase. The illustration gives a schematic representation of the dimeric molecules in the Nb phase as well as the corresponding textural and conoscopic patterns obtained

Regiocontrol in the cyclopropane ring cleavage of tricyclo[4.4.0.01,3][4.4.0.0^{1,3}]decanes to hydrindane and decalin systems

Lithium-liquid ammonia reduction of the cyclopropyl β-ketoester $2$ furnished a 1:1 mixture of hydrindane and decalin systems $3$ and $4$. Whereas under the same conditions the ketones $5$ and $6$ furnished the hydrindanones $10$ and $13$; and the hydroxy ester $7$ furnished the decalin system $14$, via the regiospecific cleavage of either $C_3--C_2$ bond or $C_3--C_1$bond

Regiocontrol in the cyclopropane ring cleavage of tricyclo[4.4.0.0<SUP>1,3</SUP>]decanes to hydrindane and decalin systems

Lithium-liquid ammonia reduction of the cyclopropyl &#946;-ketoester 2&#x0332; furnished a 1:1 mixture of hydrindane and decalin systems 3&#x0332; and 4&#x0332;. Whereas under the same conditions the ketones 5&#x0332; and 6&#x0332; furnished the hydrindanones 10&#x0332; and 13&#x0332;; and the hydroxy ester 7&#x0332; furnished the decalin system 14&#x0332;, via the regiospecific cleavage of either C3&#8212;C2 bond or C3&#8212;C1 bond

Structure–Property Correlations in Cyanobiphenyl-Based Dimer-Like Mesogens

In this contribution, we present the results of our extensive investigations on the synthesis and phase behavior of five series of dimer-like compounds formed by covalently linking a promesogenic, cyanobiphenyl core, with a nonmesogenic <i>N</i>-(<i>n</i>-alkyl)-salicylaldimine segment via an oxy­(oligomethylene)­oxy spacer of varying length and parity. This work is a continuation of our previous short study where the occurrence of re-entrant nematic (N_re) phase seemed to be vitally dependent on the parity of the spacer and the length of the terminal chain. Thus, working along these lines the effects on the thermal (N_re phase) behavior of the various spacers and the terminal tails have been investigated comprehensively. In particular, with the aim of exploring the fundamental relationships between molecular structural features and thermal properties, five spacers, namely, oxy­(hexyl)­oxy, oxy­(heptyl)­oxy, oxy­(octyl)­oxy, oxy­(nonyl)­oxy, and oxy­(decyl)­oxy spacers, have been used. Each series consists of six mesogens, as the terminal tail attached to the salicylaldimine core has been varied from <i>n</i>-pentyl to <i>n</i>-decyl. For the sake of comparison and completeness, previously reported materials have also been studied in detail, and data are included here. The characterization results derived from the optical and calorimetric studies clearly illustrate a pronounced odd–even effect; however, the effect attenuates as the length of the spacer is elongated. The even-members show higher clearing temperatures and enthalpies of transition than those of adjoining odd-members. Three series of mesogens possessing an even-parity spacer show thermodynamically stable nematic (N) and/or smectic A (SmA) phase(s); the lower homologues display only the N phase, and the middle ones exhibit both N and SmA phases while the higher members show the SmA phase solely. In contrast, the vast majority of the odd-spaced compounds of two series show a monotropic N phase. X-ray diffraction study confirms the partial bilayer order of the SmA (SmA_d) phase with <i>L</i> < <i>d</i> < 2<i>L</i> where <i>d</i> is the layer spacing and <i>L</i> is the molecular length. Contrary to what was previously noted, none of the new compounds synthesized favor the stabilization of the N_re phase. At the present time, it is extremely difficult to point out the exact cause for the origin of re-entrant behavior in some compounds exclusively, as they hardly differ in their structure. It was also found that the phase transitional properties of even-members are comparable to that observed for 4′-<i>n</i>-alkoxy-4-cyanobiphenyls (<i>n</i>OCBs) and 4-<i>n</i>-alkyl-4-cyanobiphenyls (<i>n</i>CBs). In essence, our study validates the point that dimer-like compounds resemble liquid crystal (LC) dimers, as well as monomers to some degree, in the context of their thermal behavior; thus, they can be regarded as the bridging structures between LC monomers and dimers

Aggregation and mesomorphic properties of 'double-headed' carbohydrate amphiphiles

Sugar-based amphiphiles, consisting of two sugar head groups and an alkylene chain within the molecules, are synthesized and their aggregation and mesomorphic properties are evaluated. The hydrophilic sugar head groups, constituted with β-D-glucopyranoside units, and the lyophilic alkylene units, are coupled to a glycerol backbone to afford the 'double-headed' sugar amphiphiles. Aggregation studies in aqueous solutions provided their critical micellar concentrations and the aggregation numbers. Mesophase characterizations by polarizing optical microscopy and differential scanning calorimetry (DSC) revealed the phase-transition behaviour of these new 'double-headed' glycolipids

Chemoselective Reductive Deoxygenation Of Alpha,Beta-Unsaturated Ketones And Allyl Alcohols

A simple and convenient procedure for a highly chemoselective reductive deoxygenation of alpha,beta-unsaturated ketones and allyl alcohols to olefins by sodium cyanoborohydride and boron trifluoride etherate in dry THF is described

Chemoselective reductive deoxygenation of α,β-unsaturated ketones and allyl alcohols

A simple and convenient procedure for a highly chemoselective reductive deoxygenation of α,β-unsaturated ketones and allyl alcohols to olefins by sodium cyanoborohydride and boron trifluoride etherate in dry THF is described

Aggregation and mesomorphic properties of 'double-headed' carbohydrate amphiphiles

Sugar-based amphiphiles, consisting of two sugar head groups and an alkylene chain within the molecules, are synthesized and their aggregation and mesomorphic properties are evaluated. The hydrophilic sugar head groups, constituted with beta-D-glucopyranoside units, and the lyophilic alkylene units, are coupled to a glycerol backbone to afford the 'double-headed' sugar amphiphiles. Aggregation studies in aqueous solutions provided their critical micellar concentrations and the aggregation numbers. Mesophase characterizations by polarizing optical microscopy and differential scanning calorimetry (DSC) revealed the phase-transition behaviour of these new 'double-headed' glycolipids

Aggregation and mesomorphic properties of 'double-headed' carbohydrate amphiphiles

Sugar-based amphiphiles, consisting of two sugar head groups and an alkylene chain within the molecules, are synthesized and their aggregation and mesomorphic properties are evaluated. The hydrophilic sugar head groups, constituted with β-D-glucopyranoside units, and the lyophilic alkylene units, are coupled to a glycerol backbone to afford the ‘double-headed’ sugar amphiphiles. Aggregation studies in aqueous solutions provided their critical micellar concentrations and the aggregation numbers. Mesophase characterizations by polarizing optical microscopy and differential scanning calorimetry (DSC) revealed the phase-transition behaviour of these new ‘double-headed’ glycolipids