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Lehmann A, Alaasar M, Poppe M, Poppe S, Prehm M, Nagaraj M, Sreenilayam SP, Panarin YP, Vij JK, Tschierske C. Stereochemical Rules Govern the Soft Self-Assembly of Achiral Compounds: Understanding the Heliconical Liquid-Crystalline Phases of Bent-Core Mesogens. Chemistry 2020; 26:4714-4733. [PMID: 31859404 PMCID: PMC7186843 DOI: 10.1002/chem.201904871] [Citation(s) in RCA: 19] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2019] [Revised: 12/15/2019] [Indexed: 11/16/2022]
Abstract
A series of bent-shaped 4-cyanoresorcinol bisterephthalates is reported. Some of these achiral compounds spontaneously form a short-pitch heliconical lamellar liquid-crystalline phase with incommensurate 3-layer pitch and the helix axis parallel to the layer normal. It is observed at the paraelectric-(anti)ferroelectric transition, if it coincides with the transition from random to uniform tilt and with the transition from anticlinic to synclinic tilt correlation of the molecules in the layers of the developing tilted smectic phase. For compounds with long chains the heliconical phase is only field-induced, but once formed it is stable in a distinct temperature range, even after switching off the field. The presence of the helix changes the phase properties and the switching mechanism from the naturally preferred rotation around the molecular long axis, which reverses the chirality, to a precession on a cone, which retains the chirality. These observations are explained by diastereomeric relations between two coexisting modes of superstructural chirality. One is the layer chirality, resulting from the combination of tilt and polar order, and the other one is the helical twist evolving between the layers. At lower temperature the helical structure is replaced by a non-tilted and ferreoelectric switching lamellar phase, providing an alternative non-chiral way for the transition from anticlinic to synclinic tilt.
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Affiliation(s)
- Anne Lehmann
- Department of ChemistryMartin Luther University Halle-WittenbergKurt Mothes Str. 206120Halle (Saale)Germany
| | - Mohamed Alaasar
- Department of ChemistryMartin Luther University Halle-WittenbergKurt Mothes Str. 206120Halle (Saale)Germany
- Department of ChemistryCairo University12613GizaEgypt
| | - Marco Poppe
- Department of ChemistryMartin Luther University Halle-WittenbergKurt Mothes Str. 206120Halle (Saale)Germany
| | - Silvio Poppe
- Department of ChemistryMartin Luther University Halle-WittenbergKurt Mothes Str. 206120Halle (Saale)Germany
| | - Marko Prehm
- Department of ChemistryMartin Luther University Halle-WittenbergKurt Mothes Str. 206120Halle (Saale)Germany
| | - Mamatha Nagaraj
- Department of Electronic and Electrical EngineeringTrinity College, Dublin, The University of DublinDublin2Ireland
| | - Sithara P. Sreenilayam
- Department of Electronic and Electrical EngineeringTrinity College, Dublin, The University of DublinDublin2Ireland
| | - Yuri P. Panarin
- Department of Electronic and Electrical EngineeringTrinity College, Dublin, The University of DublinDublin2Ireland
| | - Jagdish K. Vij
- Department of Electronic and Electrical EngineeringTrinity College, Dublin, The University of DublinDublin2Ireland
| | - Carsten Tschierske
- Department of ChemistryMartin Luther University Halle-WittenbergKurt Mothes Str. 206120Halle (Saale)Germany
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2
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Yadav N, Swaminathan V, Panov VP, Dhar R, Vij JK. Elucidation of the de Vries behavior in terms of the orientational order parameter, apparent tilt angle, and field-induced tilt angle for smectic liquid crystals by polarized infrared spectroscopy. Phys Rev E 2019; 100:052704. [PMID: 31870006 DOI: 10.1103/physreve.100.052704] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2019] [Indexed: 11/07/2022]
Abstract
We report experimental results of the orientational order parameter, the apparent tilt angle, and the field-induced tilt angle for three chiral smectic liquid crystalline materials investigated using infrared (IR) polarized spectroscopy. The common feature in these materials is use of the core 5-methyl-2- pyrimidine benzoate as the central part of the mesogen. This core is terminated by siloxane or carbosilane chains on one of the ends and by the chiral alkoxy chains on the opposite. These compounds exhibit low concomitant layer shrinkage at the smectic A^{*} (SmA^{*}) to smectic C^{*} (SmC^{*}) transition temperature and within the SmC^{*} phase itself. The maximum layer shrinkage in SmC^{*} is observed as ∼1.5%. We calculate the apparent orientational order parameter, S_{app} in the laboratory reference frame from the observed IR absorbance for homeotropic aligned samples, and the true order parameter, S, is calculated using the measured tilt angle and is also interpolated from Iso-SmA^{*} transition temperature closer to SmC^{*} phase. The apparent tilt angle in the SmA^{*} phase calculated from a comparison of order parameters S and S_{app} is found to be significantly large. A low magnitude of S_{app} found for homeotropic aligned samples in the SmA^{*} phase indicates that the order parameter plays a vital role in determining the de Vries characteristics, especially of exhibiting larger apparent tilt angles. Furthermore there is a significant increase in the true order parameter at temperatures close to SmA^{*} to SmC^{*} transition temperature in all three compounds. The planar-aligned samples are used to study the dependence of induced tilt angle on the applied electric field. The generalized Langevin-Debye model given by Shen et al. reasonably fits the experimental data on the field-induced tilt angle. The results show that the dipole moment of the tilt correlated domain in SmA^{*} diverges as temperature is lowered to the SmA^{*}-SmC^{*} transition temperature. The generalized Langevin-Debye model is also found to be extremely effective in confirming some of the conclusions of the de Vries behavior.
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Affiliation(s)
- Neelam Yadav
- Department of Electronic and Electrical Engineering, Trinity College Dublin, University of Dublin, Dublin 2, Ireland.,Centre of Materials Sciences, University of Allahabad, Allahabad, India
| | - V Swaminathan
- Department of Electronic and Electrical Engineering, Trinity College Dublin, University of Dublin, Dublin 2, Ireland
| | - V P Panov
- Department of Electronic and Electrical Engineering, Trinity College Dublin, University of Dublin, Dublin 2, Ireland.,Department of Electronic and Computer Engineering, Sungkyunkwan University, Jangan-Gu, Suwon, Republic of Korea
| | - R Dhar
- Centre of Materials Sciences, University of Allahabad, Allahabad, India
| | - J K Vij
- Department of Electronic and Electrical Engineering, Trinity College Dublin, University of Dublin, Dublin 2, Ireland
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Sreenilayam SP, Rodriguez-Lojo D, Panov VP, Swaminathan V, Vij JK, Panarin YP, Gorecka E, Panov A, Stevenson PJ. Design and investigation of de Vries liquid crystals based on 5-phenyl-pyrimidine and (R,R)-2,3-epoxyhexoxy backbone. Phys Rev E 2018; 96:042701. [PMID: 29347616 DOI: 10.1103/physreve.96.042701] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2017] [Indexed: 11/07/2022]
Abstract
Calamitic liquid crystals based on 5-phenyl-pyrimidine derivatives have been designed, synthesized, and characterized. The 5-phenyl pyrimidine core was functionalized with a chiral (R,R)-2,3-epoxyhexoxy chain on one side and either siloxane or perfluoro terminated chains on the opposite side. The one involving a perfluorinated chain shows SmA^{*} phase over a wide temperature range of 82 °C, whereas the siloxane analog exhibits both SmA^{*} and SmC^{*} phases over a broad range of temperatures, and a weak first-order SmA^{*}-SmC^{*} transition is observed. For the siloxane analog, the reduction factor for the layer shrinkage R (relative to its thickness at the SmA^{*}-SmC^{*} transition temperature, T_{AC}) is ∼0.373, and layer shrinkage is 1.7% at a temperature of 13 °C below the T_{AC}. This compound is considered to have "de Vries smectic" characteristics with the de Vries coefficient C_{deVries} of ∼0.86 on the scale of zero (maximum-layer shrinkage) to 1 (zero-layer shrinkage). A three-parameter mean-field model is introduced for the orientational distribution function (ODF) to reproduce the electro-optic properties. This model explains the experimental results and leads to the ODF, which exhibits a crossover from the sugar-loaf to diffuse-cone ODF some 3 °C above T_{AC}.
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Affiliation(s)
- S P Sreenilayam
- Department of Electronic and Electrical Engineering, Trinity College Dublin, The University of Dublin, Dublin 2, Ireland
| | - D Rodriguez-Lojo
- School of Chemistry and Chemical Engineering, Queens University, Belfast BT7 1NN, United Kingdom
| | - V P Panov
- Department of Electronic and Electrical Engineering, Trinity College Dublin, The University of Dublin, Dublin 2, Ireland
| | - V Swaminathan
- Department of Electronic and Electrical Engineering, Trinity College Dublin, The University of Dublin, Dublin 2, Ireland
| | - J K Vij
- Department of Electronic and Electrical Engineering, Trinity College Dublin, The University of Dublin, Dublin 2, Ireland
| | - Yu P Panarin
- Department of Electronic and Electrical Engineering, Trinity College Dublin, The University of Dublin, Dublin 2, Ireland.,School of Electrical and Electronic Engineering, Dublin Institute of Technology, Dublin 8, Ireland
| | - E Gorecka
- Department of Chemistry, Warsaw University, Al. Zwirki i Wigury 101, 02089 Warsaw, Poland
| | - A Panov
- School of Chemistry and Chemical Engineering, Queens University, Belfast BT7 1NN, United Kingdom
| | - P J Stevenson
- School of Chemistry and Chemical Engineering, Queens University, Belfast BT7 1NN, United Kingdom
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Yadav N, Panov VP, Swaminathan V, Sreenilayam SP, Vij JK, Perova TS, Dhar R, Panov A, Rodriguez-Lojo D, Stevenson PJ. Chiral smectic-A and smectic-C phases with de Vries characteristics. Phys Rev E 2017; 95:062704. [PMID: 28709233 DOI: 10.1103/physreve.95.062704] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2017] [Indexed: 11/07/2022]
Abstract
Infrared and dielectric spectroscopic techniques are used to investigate the characteristics of two chiral smectics, namely, 1,1,3,3,5,5,5-heptamethyltrisiloxane 1-[4^{'}-(undecyl-1-oxy)-4-biphenyl(S,S)-2-chloro-3-methylpentanoate] (MSi_{3}MR_{11}) and tricarbosilane-hexyloxy-benzoic acid (S)-4'-(1-methyl-hexyloxy)-3'-nitro-biphenyl-4-yl ester (W599). The orientational features and the field dependencies of the apparent tilt angle and the dichroic ratio for homogeneous planar-aligned samples were calculated from the absorbance profiles obtained at different temperatures especially in the smectic-A* phase of these liquid crystals. The dichroic ratios of the C-C phenyl ring stretching vibrations were considered for the determination of the tilt angle at different temperatures and different voltages. The low values of the order parameter obtained with and without an electric field applied across the cell in the Sm-A^{*} phase for both smectics are consistent with the de Vries concept. The generalized Langevin-Debye model introduced in the literature for explaining the electro-optical response has been applied to the results from infrared spectroscopy. The results show that the dipole moment of the tilt-correlated domain diverges as the transition temperature from Sm-A^{*} to Sm-C^{*} is approached. The Debye-Langevin model is found to be extremely effective in confirming some of the conclusions of the de Vries chiral smectics and gives additional results on the order parameter and the dichroic ratio as a function of the field across the cell. Dielectric spectroscopy finds large dipolar fluctuations in the Sm-A^{*} phase for both compounds and again these confirm their de Vries behavior.
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Affiliation(s)
- Neelam Yadav
- Department of Electronic and Electrical Engineering, Trinity College Dublin, University of Dublin, Dublin 2, Ireland.,Centre of Material Sciences, University of Allahabad, Allahabad 211002, India
| | - V P Panov
- Department of Electronic and Electrical Engineering, Trinity College Dublin, University of Dublin, Dublin 2, Ireland
| | - V Swaminathan
- Department of Electronic and Electrical Engineering, Trinity College Dublin, University of Dublin, Dublin 2, Ireland
| | - S P Sreenilayam
- Department of Electronic and Electrical Engineering, Trinity College Dublin, University of Dublin, Dublin 2, Ireland
| | - J K Vij
- Department of Electronic and Electrical Engineering, Trinity College Dublin, University of Dublin, Dublin 2, Ireland
| | - T S Perova
- Microelectronics Group, Department of Electronic and Electrical Engineering, Trinity College, University of Dublin, Dublin 2, Ireland
| | - R Dhar
- Centre of Material Sciences, University of Allahabad, Allahabad 211002, India
| | - A Panov
- School of Chemistry & Chemical Engineering, Queens University, Belfast BT7 1NN, United Kingdom
| | - D Rodriguez-Lojo
- School of Chemistry & Chemical Engineering, Queens University, Belfast BT7 1NN, United Kingdom
| | - P J Stevenson
- School of Chemistry & Chemical Engineering, Queens University, Belfast BT7 1NN, United Kingdom
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Sreenilayam SP, Agra-Kooijman DM, Panov VP, Swaminathan V, Vij JK, Panarin YP, Kocot A, Panov A, Rodriguez-Lojo D, Stevenson PJ, Fisch MR, Kumar S. Phase behavior and characterization of heptamethyltrisiloxane-based de Vries smectic liquid crystal by electro-optics, x rays, and dielectric spectroscopy. Phys Rev E 2017; 95:032701. [PMID: 28415229 DOI: 10.1103/physreve.95.032701] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2016] [Indexed: 11/07/2022]
Abstract
A heptamethyltrisiloxane liquid crystal (LC) exhibiting I-SmA^{*}-SmC^{*} phases has been characterized by calorimetry, polarizing microscopy, x-ray diffraction, electro-optics, and dielectric spectroscopy. Observations of a large electroclinic effect, a large increase in the birefringence (Δn) with electric field, a low shrinkage in the layer thickness (∼1.75%) at 20 °C below the SmA^{*}-SmC^{*} transition, and low values of the reduction factor (∼0.40) suggest that the SmA^{*} phase in this material is of the de Vries type. The reduction factor is a measure of the layer shrinkage in the SmC^{*} phase and it should be zero for an ideal de Vries. Moreover, a decrease in the magnitude of Δn with decreasing temperature indicates the presence of the temperature-dependent tilt angle in the SmA^{*} phase. The electro-optic behavior is explained by the generalized Langevin-Debye model as given by Shen et al. [Y. Shen et al., Phys. Rev. E 88, 062504 (2013)10.1103/PhysRevE.88.062504]. The soft-mode dielectric relaxation strength shows a critical behavior when the system goes from the SmA^{*} to the SmC^{*} phase.
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Affiliation(s)
- S P Sreenilayam
- Department of Electronic and Electrical Engineering, Trinity College, The University of Dublin, Dublin 2, Ireland
| | | | - V P Panov
- Department of Electronic and Electrical Engineering, Trinity College, The University of Dublin, Dublin 2, Ireland
| | - V Swaminathan
- Department of Electronic and Electrical Engineering, Trinity College, The University of Dublin, Dublin 2, Ireland
| | - J K Vij
- Department of Electronic and Electrical Engineering, Trinity College, The University of Dublin, Dublin 2, Ireland
| | - Yu P Panarin
- Department of Electronic and Electrical Engineering, Trinity College, The University of Dublin, Dublin 2, Ireland.,School of Electrical and Electronic Engineering, Dublin Institute of Technology, Dublin 8, Ireland
| | - A Kocot
- Institute of Physics, Silesian University, Katowice 40-007, Poland
| | - A Panov
- School of Chemistry and Chemical Engineering, Queens University, Belfast, BT7 1NN, United Kingdom
| | - D Rodriguez-Lojo
- School of Chemistry and Chemical Engineering, Queens University, Belfast, BT7 1NN, United Kingdom
| | - P J Stevenson
- School of Chemistry and Chemical Engineering, Queens University, Belfast, BT7 1NN, United Kingdom
| | - Michael R Fisch
- College of Applied Engineering Sustainability and Technology, Kent State University, Kent, Ohio 44242, USA
| | - Satyendra Kumar
- Department of Physics, Kent State University, Kent, Ohio 44242, USA.,Division of Research and Department of Physics, University at Albany, Albany, New York 12222, USA
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6
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Ryu SH, Shin TJ, Gong T, Shen Y, Korblova E, Shao R, Walba DM, Clark NA, Yoon DK. Cybotactic behavior in the de Vries smectic-A* liquid-crystal structure formed by a silicon-containing molecule. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2014; 89:032502. [PMID: 24730859 DOI: 10.1103/physreve.89.032502] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/17/2013] [Indexed: 06/03/2023]
Abstract
We have identified a metastable liquid-crystal (LC) structure in the de Vries smectic-A* phase (de Vries Sm-A*) formed by silicon-containing molecules under certain boundary conditions. The phase transition with the metastable structure was observed in a LC droplet placed on a planar aligned substrate and LCs confined in the groove of a silicon microchannel. During the rapid cooling step, a batonnet structure was generated as an intermediate and metastable state prior to the transition that yielded the thermodynamically stable toric focal conic domains. This distinctive behavior was characterized using depolarized reflection light microscopy and grazing incidence x-ray diffraction techniques. We concluded that the silicon groups in the molecules that formed the de Vries phase induced the formation of layered clusters called cybotactic structures. This observation is relevant to an exploration of the physical properties of cybotactic de Vries phases and gives a hint as to their optoelectronic applications.
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Affiliation(s)
- Seong Ho Ryu
- Graduate School of Nanoscience and Technology and KINC, KAIST, Daejeon, 305-701, Republic of Korea
| | - Tae Joo Shin
- Pohang Accelerator Laboratory, POSTECH, Pohang, 790-784, Republic of Korea
| | - Tao Gong
- Department of Chemistry and Liquid Crystal Materials Research Center, University of Colorado, Boulder, Colorado 80309, USA
| | - Yongqiang Shen
- Department of Physics and Liquid Crystal Materials Research Center, University of Colorado, Boulder, Colorado 80309, USA
| | - Eva Korblova
- Department of Chemistry and Liquid Crystal Materials Research Center, University of Colorado, Boulder, Colorado 80309, USA
| | - Renfan Shao
- Department of Physics and Liquid Crystal Materials Research Center, University of Colorado, Boulder, Colorado 80309, USA
| | - David M Walba
- Department of Chemistry and Liquid Crystal Materials Research Center, University of Colorado, Boulder, Colorado 80309, USA
| | - Noel A Clark
- Department of Physics and Liquid Crystal Materials Research Center, University of Colorado, Boulder, Colorado 80309, USA
| | - Dong Ki Yoon
- Graduate School of Nanoscience and Technology and KINC, KAIST, Daejeon, 305-701, Republic of Korea
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García T, Larios-López L, Rodríguez-González RJ, Torres-Lubián JR, Navarro-Rodríguez D. Azo Monomers Exhibiting Low Layer Shrinkage at the SmA-SmC Transition andtrans-cisLight-Induced Isomerization. Chemphyschem 2012. [DOI: 10.1002/cphc.201200585] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
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8
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Manna U, Richardson RM, Fukuda A, Vij JK. X-ray diffraction study of ferroelectric and antiferroelectric liquid crystal mixtures exhibiting de Vries SmA∗-SmC∗ transitions. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2010; 81:050701. [PMID: 20866175 DOI: 10.1103/physreve.81.050701] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/20/2010] [Revised: 04/01/2010] [Indexed: 05/29/2023]
Abstract
In this Rapid Communication, results on smectic layer thickness, using synchrotron radiation x-ray diffraction, for different mixtures of ferroelectric and antiferroelectric liquid crystals are given. We find that with an increased ferroelectric component in the mixtures, the layer shrinkage at the de Vries SmA∗-SmC∗ transition increases. This observation can be used to explain our previously observed behaviors [U. Manna, J.-K. Song, Yu. P. Panarin, A. Fukuda, and J. K. Vij, Phys. Rev. E 77, 041707 (2008)] that the soft-mode dielectric strength decreases, the Landau coefficient increases, and the Curie-Weiss temperature range decreases with increased ferroelectric component in the mixture exhibiting de Vries SmA∗-SmC∗ transition.
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Affiliation(s)
- U Manna
- Department of Electronic and Electrical Engineering, Trinity College, University of Dublin, Dublin 2, Ireland
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