Optically active, three-ring calamitic liquid crystals: the occurrence of frustrated, helical and polar fluid mesophases

Veerabhadraswamy, B. N.; Rao, D. S. Shankar; Prasad, S. Krishna; Yelamaggad, C. V.

doi:10.1039/c4nj02011a

Cited by 19 publications

(16 citation statements)

References 88 publications

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“…Three known FLC materials belonging to a known homologous series 37 have been used for the present dielectric studies. They show three enantiotropic mesophases, viz.…”

Section: Flc Materials and Methodsmentioning

confidence: 99%

“…BP-I/II, N* and SmC* phases, besides a monotropic SmX phase. The chosen compounds were synthesized accor ding to a reported procedure 37 and characterized by standard different spectroscopic methods. The required chemicals, namely 4-hydroxybenzaldehyde, 4-nitrophenol, acetic acid, 10% Pd-C, (R)-2-octanol, diisopropyl azodicarboxylate (DIAD), triphenylphosphine (PPh3), n-bromoalkanes, N,N′-dicyclohexylcarbodiimide (DCC) and 4-dimethylaminopyridine (DMAP), were procured either from overseas sources or local companies.…”

Section: Flc Materials and Methodsmentioning

confidence: 99%

“…As reported earlier, each profile of the compounds showed a single polarization current peak for each half-period, indicating a ferroelectric switching behavior of the SmC* phase. 37…”

Section: Flc Materials and Methodsmentioning

confidence: 99%

“…The optical textural patterns exhibited by the LC phases of these compounds, such as BP-I/II, N*, SmC* and SmX phases, were found to be precisely matching with the ones reported earlier. 37,38 The samples placed between untreated glass substrates were heated to their isotropic phase and cooled slowly. A striking platelet textural pattern of the BP-I/II phase, consisting of plates of different colors [ Fig.…”

Section: Mesomorphism Of Flc Materialsmentioning

confidence: 99%

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Dielectric study of three homologous Schiff base ferroelectric liquid crystals with the variations of temperature and frequency

et al. 2020

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In this investigation, the dielectric behaviors of three ferroelectric liquid crystals (FLCs) belonging to a homologous series have been revealed in the frequency range of 10 Hz–10 MHz. FLCs used in this study are three-ring calamitic LCs, namely ([Formula: see text])-4-(((4-(octan-2-yloxy)phenyl)imino)methyl)phenyl 4-([Formula: see text]-octyloxy)benzoate, ([Formula: see text])-4-(((4-(octan-2-yloxy)phenyl)imino)methyl)phenyl 4-([Formula: see text]-decyloxy)benzoate and ([Formula: see text])-4-(((4-(octan-2-yloxy)phenyl)imino)methyl)phenyl 4-([Formula: see text]-undecyloxy)benzoate. The polarizing optical microscopic and differential scanning calorimetric results confirm that these compounds, synthesized as per the known synthetic steps, show not only a ferroelectrically switchable chiral smectic C (SmC[Formula: see text]) phase over a wide thermal range, but also other mesophases such as blue phase-I/II (BP-I/II), chiral nematic (N[Formula: see text]) and unknown smectic (SmX) phases. Several essential dielectric parameters of the FLC phase have been measured at different temperatures. The relative permittivity has been measured with the variations of temperature and frequency. Besides, the dielectric loss and tan [Formula: see text] have been measured. Different dielectric relaxations have been calculated and explained at the molecular level. The systematic measurements revealed a strong anomaly, and crossover of relative permittivity values for the FLCs has been determined at selective frequencies between 1 kHz and 20 kHz. Strong dielectric anomaly/fall for the response function infers the involvement of collective response of dipolar assembly confined to ferroelectric Weiss domains.

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“…Three known FLC materials belonging to a known homologous series 37 have been used for the present dielectric studies. They show three enantiotropic mesophases, viz.…”

Section: Flc Materials and Methodsmentioning

confidence: 99%

Section: Flc Materials and Methodsmentioning

confidence: 99%

“…As reported earlier, each profile of the compounds showed a single polarization current peak for each half-period, indicating a ferroelectric switching behavior of the SmC* phase. 37…”

Section: Flc Materials and Methodsmentioning

confidence: 99%

Section: Mesomorphism Of Flc Materialsmentioning

confidence: 99%

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Dielectric study of three homologous Schiff base ferroelectric liquid crystals with the variations of temperature and frequency

et al. 2020

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“…[59][60][61] The reactiono f2 ,4-dihydroxybenzaldehyde with cyanobiphenyls (1a-h) in the presenceo famild base in butanone yielded the respective O-alkylated products, namely,4 '-((w-(4-formyl-3-hydroxyphenoxy)alkyl)oxy)-4-cyanobiphenyls (2a-h). [58][59][60][61][62] Under Mitsunobu reaction conditions, [63] 4-nitrophenol was O-alkylated with the (S)-and (R)-2-octanol, to obtain (R)-4-(octan-2-yloxy)nitrobenzene (3)a nd (S)-4-(octan-2-yloxy)nitrobenzenes (5); [64][65][66][67][68] these nitro materials were catalytically hydrogenated using H 2 (1 atm, balloon) and Pd/C (10 %) in THF,t oo btain the respective (R)-4-(octan-2-yloxy)aniline (4)a nd (S)-4-(octan-2yloxy)aniline (6)i nn otable yields. [64][65][66][67][68] In the final step, anilines 4 and 6 were condensed with aldehydes 2a-h in the presence of aw eak acidi ne thanol to obtain the targeted optically active, non-symmetric dimers in excellent yields.…”

Section: Synthesis and Molecular Structural Characterizationmentioning

confidence: 99%

Optically Biaxial, Re‐entrant and Frustrated Mesophases in Chiral, Non‐symmetric Liquid Crystal Dimers and Binary Mixtures

Padmini

Babu

Nair

et al. 2016

Chemistry An Asian Journal

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Sixteen optically active, non-symmetric dimers, in which cyanobiphenyl and salicylaldimine mesogens are interlinked by a flexible spacer, were synthesized and characterized. While the terminal chiral tail, in the form of either (R)-2-octyloxy or (S)-2-octyloxy chain attached to salicylaldimine core, was held constant, the number of methylene units in the spacer was varied from 3 to 10 affording eight pairs of (R & S) enantiomers. They were probed for their thermal properties with the aid of orthoscopy, conoscopy, differential scanning calorimetry and X-ray powder diffraction. In addition, the binary mixture study was carried out using chiral and achiral dimers with the intensions of stabilizing optically biaxial phase/s, re-entrant phases and important phase sequences. Notably, one of the chiral dimers as well as some mixtures exhibited a biaxial smectic A (SmA ) phase appearing between a uniaxial SmA and a re-entrant uniaxial SmA phases. The mesophases such as chiral nematic (N*) and frustrated phases viz., blue phases (BPs) and twist grain boundary (TGB) phases, were also found to occur in most of the dimers and mixtures. X-ray diffraction studies revealed that the dimers possessing oxybutoxy and oxypentoxy spacers show interdigitated (SmA ) phase where smectic periodicity is over 1.4 times the molecular length; whereas in the intercalated SmA (SmA ) phase formed by a dimer having oxydecoxy spacer the periodicity was found to be approximately half the molecular length. The handedness of the helical structure of the N* phases formed by two enantiomers was examined with the aid of CD measurements; as expected, these enantiomers showed optical activities of equal magnitudes but with opposite signs. Overall, it appears that the chiral dimers and mixtures presented herein may serve as model systems in design and developing novel materials exhibiting the apolar SmA phase possessing D symmetry and nematic-type biaxiality.

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

Veerabhadraswamy

Rao

Yelamaggad

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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Optically active, three-ring calamitic liquid crystals: the occurrence of frustrated, helical and polar fluid mesophases

Abstract: Five enantiomeric (R&S) pairs of liquid crystalline Schiff-bases prepared show a ferroelectric SmC* phase, besides N* and BP phases.

Cited by 19 publications

References 88 publications

Dielectric study of three homologous Schiff base ferroelectric liquid crystals with the variations of temperature and frequency

Dielectric study of three homologous Schiff base ferroelectric liquid crystals with the variations of temperature and frequency

Optically Biaxial, Re‐entrant and Frustrated Mesophases in Chiral, Non‐symmetric Liquid Crystal Dimers and Binary Mixtures

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

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