Synthesis and Mesomorphic Characterisation of Chiral Homologues

Dave, Jayrang S.; Menon, Meera; Patel, Pratik

doi:10.1080/10587250108025027

“…The present work described herein relates to the design, preparation, and evaluation of LC and chiroptical properties of five enantiomeric pairs of three-ring calamatics derived from the salicylaldimine-core. The target molecular architecture with three benzene rings linked in an end-to-end manner has been especially chosen, owing to its inherent ability to support the stabilization of smectic phase(s). ,,− ,− The mesogens derived from an electron rich salicylaldimine-core have attracted an enormous amount of research attention owing to their sturdiness to heat and moisture, ease of derivatization and synthesis, and remarkable thermal properties. Specifically, this core has been incorporated in the fabrication of mesomorphic compounds ranging from conventional LCs viz., calamitics, − discotics, , and polymers to nonconvetional LCs such as dimers, hexacatenars, , and banana-shaped LCs. − Notably, their appealing LC behavior has been attributed to the presence of salicylaldimine segment.…”

Section: Introductionmentioning

confidence: 99%

“…Thus, in the present work, a salicylaldimine-core in the three-ring molecular architecture has been incorporated with the rationale that the resultant LCs ought to be displaying interesting LC behavior with the thermal stability and hydrolytic resistance. Furthermore, it was deliberated to join the salicylaldimine-core to a ( n -alkoxy)benzene ring via an ester (−COO−) linkage as it induces, similar to an imine (−CHN−) group, lateral polarity quite efficiently; ,,− ,− here, it was planned to vary the length of n -alkoxy tail from n -octyloxy to n -dodecyloxy to explore its effect on the phase transitional behavior of the compounds. Importantly, the insertion of chiral tails, such as ( R )-2-octyloxy and ( S )-2-octyloxy chains, in the molecular design not only accounts for the molecular chirality but helps in placing asymmetric carbon atom (stereocenter) closer to the rigid core; such a substitution improves the magnitude of polarization due to hindered rotation of the chiral moiety.…”

Section: Introductionmentioning

confidence: 99%

Stable Ferroelectric Liquid Crystals Derived from Salicylaldimine-Core

Veerabhadraswamy

¹

,

Rao

²

,

Yelamaggad

³

2015

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Five pairs of enantiomers derived from salicylaldimine-core have been prepared by condensing (R)- or (S)-4-(octan-2-yloxy)anilines with 4-formyl-3-hydroxyphenyl 4-(n-alkoxy)benzoates. They have been designed to probe the correlation between molecular structure and mesomorphism, and especially to provide stable mesogens having potential for applications in ferroelectric liquid crystal devices. Thus, they have been substituted with a chiral tail at one end and by n-alkoxy chains of varying length at the other terminal. A detailed study confirms an indistinguishable behavior of all ten mesogens exhibiting an enantiotropic chiral smectic C (SmC*) phase besides blue phase (BP) and chiral nematic (N*) phase. The SmC* phase occurring over a 50-70 °C thermal width shows ferroelectric switching with spontaneous polarization (Ps) value crossing over 100 nC/cm(2). Circular dichroism spectroscopic study of the mesophases confirms the chromophores of the molecules being in the macroscopic chiral (helical) environment.

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Design and Synthesis of Chiral Nematic Liquid Crystals

Taugerbeck

¹

,

Booth

²

2014

Handbook of Liquid Crystals

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The article contains sections titled: Introduction to the Chiral Nematic Phase and Its Properties Formulation and Application of Chiral Nematic Liquid Crystal Mixtures Applications of Chiral Nematic Phases Classification of Chiral Nematic Liquid‐Crystalline Compounds Aspects of Molecular Symmetry for Chiral Nematic Phases Type I Chiral Nematic Liquid Crystals Azobenzenes and Related Mesogens Azomethine ( S chiff's Base) Mesogens Stable Phenyl, Biphenyl, Terphenyl, and Phenylethylbiphenyl Mesogens Ester Mesogens Derivatives of Chiral Alcohols Type II Chiral Nematic Liquid Crystals Type IIa Twin Systems Using Chiral Flexible Spacers Type IIb Materials Using Achiral Flexible Spacers and Chiral Terminal Groups Type IIc and d Materials Using One or Two Chiral Cores Type III Chiral Nematic Liquid Crystals Cholesteryl Esters Chiral Mesogens Derived from Cyclohexane Chiral Heterocyclic Mesogens Axially Chiral Liquid Crystals Axially Chiral Alkenes and Overcrowded Alkenes Allenes Tricyclo[4.4.0.0 3,8 ]decane or Twistane Derived Mesogens Sterically Hindered Biphenyl Derivatives Spirobiindane Derivatives Concluding Remarks

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Ferroelectric Liquid Crystals: Synthesis and Thermal Behavior of Optically Active, Three‐Ring Schiff Bases and Salicylaldimines

Veerabhadraswamy

¹

,

Rao

²

,

Yelamaggad

³

2018

Chemistry An Asian Journal

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The chiral ferroelectric smectic C (SmC*) phase, characterized by a helical superstructure, has been well exploited in developing high-resolution microdisplays that have been effectively employed in the fabrication of a wide varieties of portable devices. Although, an overwhelming number of optically active (chiral) liquid crystals (LCs) exhibiting a SmC* phase have been designed and synthesized, the search for new systems continues so as to realize mesogens capable of meeting technical necessities and specifications for their end-use. In continuation of our research work in this direction, herein we report the design, synthesis, and thermal behavior of twenty new optically active, three-ring calamitic LCs belonging to four series. The first two series comprise five pairs of enantiomeric Schiff bases whereas the other two series are composed of five pairs of enantiomeric salicylaldimines. In each pair of optical isomers, the configuration of a chiral center in one stereoisomer is opposite to that of the analogous center in the other isomer as they are derived from (3 S)-3,7-dimethyloctyloxy and (3 R)-3,7-dimethyloctyloxy tails. To probe the structure-property correlations in each series, the length of the n-alkoxy tail situated at the other end of the mesogens has been varied from n-octyloxy to n-dodecyloxy. The measurement of optical activity of these chiral mesogens was carried out by recording their specific rotations. As expected, enantiomers rotate plane polarized light in the opposite direction but by the same magnitude. The thermal behavior of the compounds was established by using a combination of optical polarizing microscopy, differential scanning calorimetry, and powder X-ray diffraction. These complementary techniques demonstrate the existence of the expected, thermodynamically stable, chiral smectic C (SmC*) LC phase besides blue phase I/II (BPI or BPII) and chiral nematic (N*) phase. However, as noted in our previous analogous study, the vast majority of the Schiff bases show an additional metastable, unfamiliar smectic (SmX) phase just below the SmC* phase. Notably, the SmC* phase persists over the temperature range ≈80-115 °C. Two mesogens chosen each from Schiff bases and salicylaldimines were investigated for their electrical switching behavior. The study reveals the ferroelectric switching characteristics of the SmC* phase featuring the spontaneous polarization (P ) in the range 69-96 nC cm . The helical twist sense of the SmC* phase as well as the N* phase formed by a pair of enantiomeric Schiff bases and salicylaldimines has been established with the help of circular dichroism (CD) spectroscopic technique. As expected, the SmC* and the N* phase of a pair of enantiomers showed mirror image CD signals. Most importantly, the reversal of helical handedness from left to right and vice versa has been evidenced during the N* to SmC* phase transition, implying that the screw sense of the helical array of the N* phase and the SmC* phase of an enantiomer is opposite.

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Synthesis and Mesomorphic Characterisation of Chiral Homologues

Cited by 15 publications

References 7 publications

Stable Ferroelectric Liquid Crystals Derived from Salicylaldimine-Core

Stable Ferroelectric Liquid Crystals Derived from Salicylaldimine-Core

Design and Synthesis of Chiral Nematic Liquid Crystals

Ferroelectric Liquid Crystals: Synthesis and Thermal Behavior of Optically Active, Three‐Ring Schiff Bases and Salicylaldimines

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