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Current Advances in Liquid Crystals
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Current Advances in Liquid Crystals

A special issue of Molecules (ISSN 1420-3049). This special issue belongs to the section "Macromolecular Chemistry".

Deadline for manuscript submissions: closed (31 August 2020) | Viewed by 27444

Special Issue Editor

Prof. Dr. Pradip K. Bhowmik

E-Mail Website
Guest Editor
Department of Chemistry and Biochemistry, University of Nevada Las Vegas, 4505 S. Maryland Parkway Box 454003, Las Vegas, NV 89154-4003, USA
Interests: liquid crystalline polymers; light-emitting polymers; fire retardant polymers; viologen polymers; poly(pyridinium salts); nanostructured materials; organic synthesis; polymer synthesis; green chemistry; ionic liquids; ionic liquid crystals; luminescent organic salts; anticancer drugs
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

The broad field of liquid crystals (LCs) has attracted the attention of chemists, physicists, biologists, and engineers alike since the discovery of liquid crystal phase by the Austrian botanist Friedrich Reinitzer in 1888. LC phases combine the material properties of crystals with the flow properties of liquids. As such, they have provided the foundation for a revolution in the low-power, flat-panel display technology known as LCD. Interestingly enough, many diversified, chemical–structural architectures (rod-shaped, disc-shaped, and bent-shaped) exhibit various types of LC phases that include organic molecules, main-chain and side-chain polymers, hyperbranced polymers, dedrimers, ionic molecules, and even zwitter ionic molecules, to mention a few. They have many technogical applications because of their chemical diversities and types of LC phases. For example, Kevlar—lyotropic LC aromatic polyamide—and Vectra—thermotropic aromatic LC polyester—are the basis of light-weight, high-strength materials for a numer of civilian and military applications, including their important contribution in body armor. Side-chain LC polymers are known as functional polymers for non-linear optical properties and data storage capabilities. Additionally, ionic liquid crystals (ILCs) that form columnar, smectic, and bicontinuous cubic phases can provide well-organized 1D, 2D, and 3D channels capable of transporting ions and electrons. They can be used as electrolytes for batteries and photovoltaics, semiconductors, and electroluminescence and electrochemical devices. ILCs are the reent addition to the ever-increasing field of LCs.                         

Therefore, we invite researchers to submit their articles and reviews to this Special Issue of Molecules on “Liquid Crystals” that aims to identify and review the latest research on the broad field of liquid crystals that have been demonstrated to have a great impact in molecular science. Manuscripts can be related to any aspect of liquid crystals, such as (but not limited to):

  • Synthesis of novel LCs
  • Structure–property–application of LCs
  • Novel types of LCs
  • Applications of LCs in devices
  • Biological applications of LCs
  • Physical properties of LCs
  • Computer simulations of the phase behaviour of LCs
  • Theoretical models of LCs

Prof. Dr. Pradip K. Bhowmik
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Molecules is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2700 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • Liquid crystals
  • Ionic liquid crystals
  • Zwitter ionic liquid crystals
  • Thermotropic liquid crystals
  • Lyotropic liquid crystals
  • Amphotropic liquid crystals
  • Liquid crystalline elastomers
  • Rod-shaped molecules
  • Disc-shaped molecules
  • Bent-shaped molecules

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Published Papers (15 papers)

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Editorial

Jump to: Research, Review

3 pages, 175 KiB  
Editorial
Special Issue Editorial: Current Advances in Liquid Crystals
by Pradip K. Bhowmik
Molecules 2021, 26(12), 3713; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules26123713 - 18 Jun 2021
Cited by 2 | Viewed by 1902
Abstract
The broad field of liquid crystals (LCs) has attracted the attention of chemists, physicists, biologists and engineers alike since the discovery of liquid crystalline phase by the Austrian botanist Friedrich Reinitzer in 1888 [...] Full article
(This article belongs to the Special Issue Current Advances in Liquid Crystals)

Research

Jump to: Editorial, Review

10 pages, 2094 KiB  
Article
Insertion of the Liquid Crystal 5CB into Monovacancy Graphene
by Paul A. Brown, Jakub Kołacz, Sean A. Fischer, Christopher M. Spillmann and Daniel Gunlycke
Molecules 2022, 27(5), 1664; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules27051664 - 03 Mar 2022
Cited by 1 | Viewed by 1753
Abstract
Interfacial interactions between liquid crystal (LC) and two-dimensional (2D) materials provide a platform to facilitate novel optical and electronic material properties. These interactions are uniquely sensitive to the local energy landscape of the atomically thick 2D surface, which can be strongly influenced by [...] Read more.
Interfacial interactions between liquid crystal (LC) and two-dimensional (2D) materials provide a platform to facilitate novel optical and electronic material properties. These interactions are uniquely sensitive to the local energy landscape of the atomically thick 2D surface, which can be strongly influenced by defects that are introduced, either by design or as a byproduct of fabrication processes. Herein, we present density functional theory (DFT) calculations of the LC mesogen 4-cyan-4′-pentylbiphenyl (5CB) on graphene in the presence of a monovacancy (MV-G). We find that the monovacancy strengthens the binding of 5CB in the planar alignment and that the structure is lower in energy than the corresponding homeotropic structure. However, if the molecule is able to approach the monovacancy homeotropically, 5CB undergoes a chemical reaction, releasing 4.5 eV in the process. This reaction follows a step-by-step process gradually adding bonds, inserting the 5CB cyano group into MV-G. We conclude that this irreversible insertion reaction is likely spontaneous, potentially providing a new avenue for controlling both LC behavior and graphene properties. Full article
(This article belongs to the Special Issue Current Advances in Liquid Crystals II)
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17 pages, 3293 KiB  
Article
Controlling Liquid Crystal Configuration and Phase Using Multiple Molecular Triggers
by Linda M. Oster, Jake Shechter, Benjamin Strain, Manisha Shivrayan, Sankaran Thai Thayumanavan and Jennifer L. Ross
Molecules 2022, 27(3), 878; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules27030878 - 27 Jan 2022
Cited by 2 | Viewed by 2741
Abstract
Liquid crystals are able to transform a local molecular interaction into a macroscopic change of state, making them a valuable “smart” material. Here, we investigate a novel polymeric amphiphile as a candidate for molecular triggering of liquid crystal droplets in aqueous background. Using [...] Read more.
Liquid crystals are able to transform a local molecular interaction into a macroscopic change of state, making them a valuable “smart” material. Here, we investigate a novel polymeric amphiphile as a candidate for molecular triggering of liquid crystal droplets in aqueous background. Using microscopy equipped with crossed polarizers and optical tweezers, we find that the monomeric amphiphile is able to trigger both a fast phase change and then a subsequent transition from nematic to isotropic. We next include sodium dodecyl sulfate (SDS), a standard surfactant, with the novel amphiphilic molecules to test phase transitioning when both were present. As seen previously, we find that the activity of SDS at the surface can result in configuration changes with hysteresis. We find that the presence of the polymeric amphiphile reverses the hysteresis previously observed during such transitions. This work demonstrates a variety of phase and configuration changes of liquid crystals that can be controlled by multiple exogenous chemical triggers. Full article
(This article belongs to the Special Issue Current Advances in Liquid Crystals II)
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7 pages, 16256 KiB  
Communication
Control of the Induced Handedness of Helical Nanofilaments Employing Cholesteric Liquid Crystal Fields
by Ju-Yong Kim, Jae-Jin Lee, Jun-Sung Park, Yong-Jun Choi and Suk-Won Choi
Molecules 2021, 26(19), 6055; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules26196055 - 06 Oct 2021
Cited by 2 | Viewed by 1535
Abstract
In this paper, a simple and powerful method to control the induced handedness of helical nanofilaments (HNFs) is presented. The nanofilaments are formed by achiral bent-core liquid crystal molecules employing a cholesteric liquid crystal field obtained by doping a rod-like nematogen with a [...] Read more.
In this paper, a simple and powerful method to control the induced handedness of helical nanofilaments (HNFs) is presented. The nanofilaments are formed by achiral bent-core liquid crystal molecules employing a cholesteric liquid crystal field obtained by doping a rod-like nematogen with a chiral dopant. Homochiral helical nanofilaments are formed in the nanophase-separated helical nanofilament/cholesteric phase from a mixture with a cholesteric phase. This cholesteric phase forms at a temperature higher than the temperature at which the helical nanofilament in a bent-core molecule appears. Under such conditions, the cholesteric liquid crystal field acts as a driving force in the nucleation of HNFs, realizing a perfectly homochiral domain consisting of identical helical nanofilament handedness. Full article
(This article belongs to the Special Issue Current Advances in Liquid Crystals II)
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15 pages, 2952 KiB  
Article
Mesomorphic Behavior of Symmetric Azomethine Dimers Containing Different Chromophore Groups
by Elena Perju and Luminita Marin
Molecules 2021, 26(8), 2183; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules26082183 - 10 Apr 2021
Cited by 9 | Viewed by 1878
Abstract
A series of new azomethine dimers was synthesized by the condensation reaction of flexible bis-benzaldehydes with four aromatic amines containing phenyl, naphthyl, anthracene and pyrene groups. Their right structure was confirmed by FTIR and 1H-NMR spectroscopy and their thermal properties were investigated [...] Read more.
A series of new azomethine dimers was synthesized by the condensation reaction of flexible bis-benzaldehydes with four aromatic amines containing phenyl, naphthyl, anthracene and pyrene groups. Their right structure was confirmed by FTIR and 1H-NMR spectroscopy and their thermal properties were investigated by thermogravimetric analysis, differential scanning calorimetry and polarized light optical microscopy. A view on their photophysical behavior was gained by UV-vis and photoluminescence spectroscopy. The dimers containing pyrene and anthracene presented liquid crystalline behavior, while the other dimers were crystalline compounds. Two dimers containing pyrene moieties formed mesomorphic glasses and had intense luminescence, promising properties for applications in building optoelectronic devices. Full article
(This article belongs to the Special Issue Current Advances in Liquid Crystals II)
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18 pages, 4182 KiB  
Article
Liquid Crystalline Copolymers Containing Sulfonic and Light-Responsive Groups: From Molecular Design to Conductivity
by Sakinah Mohd Alauddin, Nurul Fadhilah Kamalul Aripin, Thamil Selvi Velayutham and Alfonso Martinez-Felipe
Molecules 2020, 25(11), 2579; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules25112579 - 02 Jun 2020
Cited by 12 | Viewed by 3500
Abstract
In the search for novel smart multifunctional liquid crystalline materials, we report the synthesis, thermal and structural characterisation, and the conductivity, of a set of new block and statistical copolymers, containing light-responsive mesogenic groups (MeOAzB), polar sulfonic acids (AMPS), and methyl(methacrylate) groups (MMA). [...] Read more.
In the search for novel smart multifunctional liquid crystalline materials, we report the synthesis, thermal and structural characterisation, and the conductivity, of a set of new block and statistical copolymers, containing light-responsive mesogenic groups (MeOAzB), polar sulfonic acids (AMPS), and methyl(methacrylate) groups (MMA). By using a cascade of reversible addition-fragmentation chain polymerisations, RAFT, we have tailored different side-chain polymeric structures by controlling monomer composition (MeOAzB/AMPS/MMA) and configuration. We have yielded simultaneous liquid crystalline behaviour and appreciable conductivity in polymers with low concentrations of polar acid groups, by the formation of smectic phases in narrow aggregates. The light-responsiveness of the polymers, via reversible trans-to-cis photoisomerization of azobenzene groups, and the local activation of conductivity at relatively low temperatures, opens the possibility to prepare polymer electrolytes for energy conversion and storage, whose conductivity could be controlled and optimised by external stimuli, including light irradiation. Full article
(This article belongs to the Special Issue Current Advances in Liquid Crystals)
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20 pages, 4751 KiB  
Article
Thermotropic Liquid-Crystalline and Light-Emitting Properties of Bis(4-aalkoxyphenyl) Viologen Bis(triflimide) Salts
by Pradip K. Bhowmik, Muhammed Kareem M. Al-Karawi, Shane T. Killarney, Erenz J. Dizon, Anthony Chang, Jongin Kim, Si L. Chen, Ronald Carlo G. Principe, Andy Ho, Haesook Han, Hari D. Mandal, Raymond G. Cortez, Bryan Gutierrez, Klarissa Mendez, Lewis Sharpnack, Deña M. Agra-Kooijman, Michael R. Fisch and Satyendra Kumar
Molecules 2020, 25(10), 2435; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules25102435 - 23 May 2020
Cited by 10 | Viewed by 4936
Abstract
A series of bis(4-alkoxyphenyl) viologen bis(triflimide) salts with alkoxy chains of different lengths were synthesized by the metathesis reaction of respective bis(4-alkoxyphenyl) viologen dichloride salts, which were in turn prepared from the reaction of Zincke salt with the corresponding 4-n-alkoxyanilines, with lithium triflimide [...] Read more.
A series of bis(4-alkoxyphenyl) viologen bis(triflimide) salts with alkoxy chains of different lengths were synthesized by the metathesis reaction of respective bis(4-alkoxyphenyl) viologen dichloride salts, which were in turn prepared from the reaction of Zincke salt with the corresponding 4-n-alkoxyanilines, with lithium triflimide in methanol. Their chemical structures were characterized by 1H and 13C nuclear magnetic resonance spectra and elemental analysis. Their thermotropic liquid-crystalline (LC) properties were examined by differential scanning calorimetry, polarizing optical microscopy, and variable temperature X-ray diffraction. Salts with short length alkoxy chains had crystal-to-liquid transitions. Salts of intermediate length alkoxy chains showed both crystal-to-smectic A (SmA) transitions, Tms, and SmA-to-isotropic transitions, Tis. Those with longer length of alkoxy chains had relatively low Tms at which they formed the SmA phases that persisted up to the decomposition at high temperatures. As expected, all of them had excellent thermal stabilities in the temperature range of 330–370 °C. Their light-emitting properties in methanol were also included. Full article
(This article belongs to the Special Issue Current Advances in Liquid Crystals)
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9 pages, 2868 KiB  
Article
Optical Textures and Orientational Structures in Cholesteric Droplets with Conical Boundary Conditions
by Anna P. Gardymova, Mikhail N. Krakhalev and Victor Ya. Zyryanov
Molecules 2020, 25(7), 1740; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules25071740 - 10 Apr 2020
Cited by 9 | Viewed by 3613
Abstract
Cholesteric droplets dispersed in polymer with conical boundary conditions have been studied. The director configurations are identified by the polarising microscopy technique. The axisymmetric twisted axial-bipolar configuration with the surface circular defect at the droplet’s equator is formed at the relative chirality parameter [...] Read more.
Cholesteric droplets dispersed in polymer with conical boundary conditions have been studied. The director configurations are identified by the polarising microscopy technique. The axisymmetric twisted axial-bipolar configuration with the surface circular defect at the droplet’s equator is formed at the relative chirality parameter N 0 ≤ 2.9 . The intermediate director configuration with the deformed circular defect is realised at 2.9 < N 0 < 3.95 , and the layer-like structure with the twisted surface defect loop is observed at N 0 ≥ 3.95 . The cholesteric layers in the layer-like structure are slightly distorted although the cholesteric helix is untwisted. Full article
(This article belongs to the Special Issue Current Advances in Liquid Crystals)
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15 pages, 4223 KiB  
Article
Induced Phases of New H-bonded Supramolecular Liquid Crystal Complexes; Mesomorphic and Geometrical Estimation
by Rua B. Alnoman, Hoda A. Ahmed, Mohamed Hagar, Khulood A. Abu Al-Ola, Bedor Sh. Alrefay, Bashayer A. Haddad, Raghad F. Albalawi, Razan H. Aljuhani, Lama D. Aloqebi and Shoaa F. Alsenani
Molecules 2020, 25(7), 1549; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules25071549 - 28 Mar 2020
Cited by 18 | Viewed by 2606
Abstract
New five rings architecture of 1:1 supramolecular hydrogen bonded (H-bonded) complexes were formed between 4-(2-(pyridin-4-yl)diazenyl-3-methylphenyl 4-alkoxybenzoates and 4-n-alkoxyphenyliminobenzoic acids. Mesomorphic and optical behaviors of three systems designed complexes were investigated by differential scanning calorimetry (DSC) and polarizing optical microscopy (POM). H-bonded interactions were [...] Read more.
New five rings architecture of 1:1 supramolecular hydrogen bonded (H-bonded) complexes were formed between 4-(2-(pyridin-4-yl)diazenyl-3-methylphenyl 4-alkoxybenzoates and 4-n-alkoxyphenyliminobenzoic acids. Mesomorphic and optical behaviors of three systems designed complexes were investigated by differential scanning calorimetry (DSC) and polarizing optical microscopy (POM). H-bonded interactions were confirmed via FT-IR spectroscopy. Computational calculations were carried out by density functional theory (DFT) estimation for all formed complexes. Experimental evaluations were correlated with the theoretical predictions and results revealed that, all prepared complexes possessing enantiotropic tri-mesophases with induced smectic C (SmC) and nematic temperature ranges. Moreover, DFT predicted for all formed supramolecular complexes possessing a non-linear bent geometry. Moreover, the π–π stacking of the aromatic rings plays an important role in the mesomorphic properties and thermal stabilities of observed phases. The energy changes between frontier molecular orbitals (HOMO and LUMO) and the molecular electrostatic potential (MEP) of the designed complexes were discussed and related to the experimental results. Full article
(This article belongs to the Special Issue Current Advances in Liquid Crystals)
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16 pages, 2406 KiB  
Article
Chair- and V-Shaped of H-bonded Supramolecular Complexes of Azophenyl Nicotinate Derivatives; Mesomorphic and DFT Molecular Geometry Aspects
by Omaima A. Alhaddad, Khulood A. Abu Al-Ola, Mohamed Hagar and Hoda A. Ahmed
Molecules 2020, 25(7), 1510; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules25071510 - 26 Mar 2020
Cited by 13 | Viewed by 2243
Abstract
New geometrical architectures of chair- and V-shaped supramolecular liquid crystalline complexes were molded through 1:1 intermolecular hydrogen bonding interactions between 4-(4-(hexyloxy)phenylazo)methyl)phenyl nicotinate and 4-alkoxybenzoic acids. The length of terminal alkoxy acid chains varied, n = 6 to 16 carbons. The mesomorphic behaviour of [...] Read more.
New geometrical architectures of chair- and V-shaped supramolecular liquid crystalline complexes were molded through 1:1 intermolecular hydrogen bonding interactions between 4-(4-(hexyloxy)phenylazo)methyl)phenyl nicotinate and 4-alkoxybenzoic acids. The length of terminal alkoxy acid chains varied, n = 6 to 16 carbons. The mesomorphic behaviour of these complexes was examined through differential scanning calorimetry (DSC) and polarizing optical microscopy (POM). Fourier-transform infrared spectroscopy (FT-IR) was carried out to confirm the presence of Fermi bands that appeared for the hydrogen bonding formation. Enantiotropic nematic phases were observed and covered all lengths of alkoxy chains. The geometrical structures of the prepared supramolecular complexes geometries were estimated by Density functional theory (DFT) calculations. The supramolecular complexes I/An are projected to exhibit a nonlinear geometry with V-shaped and chair-shaped geometry. The chair-shaped conformers of I/An were found to be more stable than V-shaped isomeric complexes. Moreover, the effect of the change of the mesogenic core on the mesophase thermal stability (TC) has been investigated by a comparative study of the present azo supramolecular H-bonding LCs (SMHBCs) I/An and our previously reported their Schiff base analogue complexes, II/An. The findings of the DFT illustrated the high impact of CH=N as a mesogenic core on the mesomorphic behavior in terms of the competitive lateral and terminal intermolecular interactions as well as the molecular electrostatic potential (MEP). Full article
(This article belongs to the Special Issue Current Advances in Liquid Crystals)
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15 pages, 4215 KiB  
Article
New Symmetrical U- and Wavy-Shaped Supramolecular H-Bonded Systems; Geometrical and Mesomorphic Approaches
by Laila A. Al-Mutabagani, Latifah Abdullah Alshabanah, Hoda A. Ahmed, Mohamed Hagar and Khulood A. Abu Al-Ola
Molecules 2020, 25(6), 1420; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules25061420 - 20 Mar 2020
Cited by 18 | Viewed by 2404
Abstract
New mesomorphic symmetrical 2:1 supramolecular H-bonded complexes of seven phenyl rings were prepared between 4-n-alkoxyphenylazobenzoic acids and 4-(2-(pyridin-3-yl)diazenyl)phenyl nicotinate. Mesomorphic studies of the prepared complexes were investigated using differential scanning calorimetry (DSC) and polarizing optical microscopy (POM). Fermi bands of the formed H-bonded [...] Read more.
New mesomorphic symmetrical 2:1 supramolecular H-bonded complexes of seven phenyl rings were prepared between 4-n-alkoxyphenylazobenzoic acids and 4-(2-(pyridin-3-yl)diazenyl)phenyl nicotinate. Mesomorphic studies of the prepared complexes were investigated using differential scanning calorimetry (DSC) and polarizing optical microscopy (POM). Fermi bands of the formed H-bonded interactions were confirmed by FT-IR spectroscopy. Geometrical parameters for all complexes were performed using the density functional theory (DFT) calculations method. Theoretical results revealed that the prepared H-bonded complexes are in non-linear geometry with U-shaped and wavy-shaped geometrical structures; however, the greater linearity of the wavy-shaped compounds could be the reason for their stability with respect to the U-shaped conformer. Moreover, the stable, wavy shape of supramolecular H-bonded complexes (SMHBCs) has been used to illustrate mesomeric behavior in terms of the molecular interaction. The experimental mesomorphic investigations revealed that all complexes possess enantiotropic smectic C phase. Phases were confirmed by miscibility with a standard smectic C (SmC) compound. A comparison was constructed to investigate the effect of incorporating azophenyl moiety into the mesomeric behavior of the corresponding five-membered complexes. It was found that the addition of the extra phenylazo group to the acid moiety has a great increment of the mesophase stability (TC) values with respect to the monotropic SmC phase of the five aromatic systems to the high stable enantiotropic SmC mesophase. Full article
(This article belongs to the Special Issue Current Advances in Liquid Crystals)
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18 pages, 3719 KiB  
Article
Experimental and Theoretical Approaches of New Nematogenic Chair Architectures of Supramolecular H-Bonded Liquid Crystals
by O. A. Alhaddad, H. A. Ahmed and M. Hagar
Molecules 2020, 25(2), 365; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules25020365 - 16 Jan 2020
Cited by 34 | Viewed by 2374
Abstract
New four isomeric chair architectures of 1:1 H-bonded supramolecular complexes were prepared through intermolecular interactions between 4-(2-(pyridin-4-yl)diazenyl-(2-(or 3-)chlorophenyl) 4-alkoxybenzoates and 4-n-alkoxybenzoic acids. The H-bond formation of all complexes was confirmed by differential scanning calorimetry (DSC) and Fourier-transform infrared spectroscopy (FTIR). Mesomorphic characterization was [...] Read more.
New four isomeric chair architectures of 1:1 H-bonded supramolecular complexes were prepared through intermolecular interactions between 4-(2-(pyridin-4-yl)diazenyl-(2-(or 3-)chlorophenyl) 4-alkoxybenzoates and 4-n-alkoxybenzoic acids. The H-bond formation of all complexes was confirmed by differential scanning calorimetry (DSC) and Fourier-transform infrared spectroscopy (FTIR). Mesomorphic characterization was carried by DSC and polarized optical microscopy (POM). It was found that all prepared laterally chloro-substituted supramolecular complexes were nematogenic, and exhibited nematic phase and low melting temperature. The thermal stability of the nematic mesophase observed depends upon the location and spatial orientation of the lateral Cl− atom in as well as the length of terminal chains. Theoretical calculations were carried out within the paradigm of the density functional theory (DFT) in order to establish the molecular conformation for the formed complexes and estimate their thermal parameters. The results of the computational calculations revealed that the H-bonded complexes were in a chair form molecular geometry. Additionally, out of the acquired data, it was possible to designate the influence of the position and orientation of the lateral group as well as the alkoxy chain length on the stability of the nematic phase. Full article
(This article belongs to the Special Issue Current Advances in Liquid Crystals)
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17 pages, 3553 KiB  
Article
Synthesis, Optical, and Geometrical Approaches of New Natural Fatty Acids’ Esters/Schiff Base Liquid Crystals
by Rua Alnoman, Fares khalid Al-Nazawi, Hoda A. Ahmed and Mohamed Hagar
Molecules 2019, 24(23), 4293; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules24234293 - 25 Nov 2019
Cited by 34 | Viewed by 3029
Abstract
Schiff base liquid crystals, known as [4-(hexyloxy)phenylimino)methyl]phenyl palmitate (IA), [4-(hexyloxy)phenylimino)methyl]phenyl oleate (IIA) and [4-(hexyloxy)phenylimino)methyl]phenyl linoleate (IIIA), were synthesized from palmitic, oleic, and linoleic natural fatty acids. The prepared compounds have been investigated for their thermal and optical [...] Read more.
Schiff base liquid crystals, known as [4-(hexyloxy)phenylimino)methyl]phenyl palmitate (IA), [4-(hexyloxy)phenylimino)methyl]phenyl oleate (IIA) and [4-(hexyloxy)phenylimino)methyl]phenyl linoleate (IIIA), were synthesized from palmitic, oleic, and linoleic natural fatty acids. The prepared compounds have been investigated for their thermal and optical behavior as well as phase formation using differential scanning calorimetry (DSC) and polarized optical microscopy (POM). Molecular structures of all studied compounds were confirmed via elemental analysis, FT-IR, 1H NMR, and 13C NMR. Smectic phase is the observed mesophase for all compounds; however, their type and range depend upon the terminal alkanoate chains attached to the phenyl ring. Computational calculations, Density functional theory (DFT), energy difference of the frontier molecular orbital (FMOs), as well as the thermodynamic parameters of different molecular configurations isomers were discussed. It was found that the mesophase behavior and the geometrical characteristics were affected by the degree of unsaturation of fatty terminal chains. Furthermore, the geometrical structure of the CH=N linkage plays an important role in the thermal stability and optical transition temperature. Full article
(This article belongs to the Special Issue Current Advances in Liquid Crystals)
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Review

Jump to: Editorial, Research

36 pages, 4908 KiB  
Review
Development and Application of Liquid Crystals as Stimuli-Responsive Sensors
by Sulayman A. Oladepo
Molecules 2022, 27(4), 1453; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules27041453 - 21 Feb 2022
Cited by 17 | Viewed by 3812
Abstract
This focused review presents various approaches or formats in which liquid crystals (LCs) have been used as stimuli-responsive sensors. In these sensors, the LC molecules adopt some well-defined arrangement based on the sensor composition and the chemistry of the system. The sensor usually [...] Read more.
This focused review presents various approaches or formats in which liquid crystals (LCs) have been used as stimuli-responsive sensors. In these sensors, the LC molecules adopt some well-defined arrangement based on the sensor composition and the chemistry of the system. The sensor usually consists of a molecule or functionality in the system that engages in some form of specific interaction with the analyte of interest. The presence of analyte brings about the specific interaction, which then triggers an orientational transition of the LC molecules, which is optically discernible via a polarized optical image that shows up as dark or bright, depending on the orientation of the LC molecules in the system (usually a homeotropic or planar arrangement). The various applications of LCs as biosensors for glucose, protein and peptide detection, biomarkers, drug molecules and metabolites are extensively reviewed. The review also presents applications of LC-based sensors in the detection of heavy metals, anionic species, gases, volatile organic compounds (VOCs), toxic substances and in pH monitoring. Additionally discussed are the various ways in which LCs have been used in the field of material science. Specific attention has been given to the sensing mechanism of each sensor and it is important to note that in all cases, LC-based sensing involves some form of orientational transition of the LC molecules in the presence of a given analyte. Finally, the review concludes by giving future perspectives on LC-based sensors. Full article
(This article belongs to the Special Issue Current Advances in Liquid Crystals II)
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24 pages, 52702 KiB  
Review
Flexible Liquid Crystal Polymer Technologies from Microwave to Terahertz Frequencies
by Zepeng Zhou, Wenqing Li, Jun Qian, Weihong Liu, Yiming Wang, Xijian Zhang, Qinglei Guo, Yevhen Yashchyshyn, Qingpu Wang, Yanpeng Shi and Yifei Zhang
Molecules 2022, 27(4), 1336; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules27041336 - 16 Feb 2022
Cited by 15 | Viewed by 5429
Abstract
With the emergence of fifth-generation (5G) cellular networks, millimeter-wave (mmW) and terahertz (THz) frequencies have attracted ever-growing interest for advanced wireless applications. The traditional printed circuit board materials have become uncompetitive at such high frequencies due to their high dielectric loss and large [...] Read more.
With the emergence of fifth-generation (5G) cellular networks, millimeter-wave (mmW) and terahertz (THz) frequencies have attracted ever-growing interest for advanced wireless applications. The traditional printed circuit board materials have become uncompetitive at such high frequencies due to their high dielectric loss and large water absorption rates. As a promising high-frequency alternative, liquid crystal polymers (LCPs) have been widely investigated for use in circuit devices, chip integration, and module packaging over the last decade due to their low loss tangent up to 1.8 THz and good hermeticity. The previous review articles have summarized the chemical properties of LCP films, flexible LCP antennas, and LCP-based antenna-in-package and system-in-package technologies for 5G applications, although these articles did not discuss synthetic LCP technologies. In addition to wireless applications, the attractive mechanical, chemical, and thermal properties of LCP films enable interesting applications in micro-electro-mechanical systems (MEMS), biomedical electronics, and microfluidics, which have not been summarized to date. Here, a comprehensive review of flexible LCP technologies covering electric circuits, antennas, integration and packaging technologies, front-end modules, MEMS, biomedical devices, and microfluidics from microwave to THz frequencies is presented for the first time, which gives a broad introduction for those outside or just entering the field and provides perspective and breadth for those who are well established in the field. Full article
(This article belongs to the Special Issue Current Advances in Liquid Crystals II)
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