Thermotropic Liquid-crystalline Properties of Azomethine Dimers: Synthesis and Characterisation | Chapter 5 | Recent Developments in Chemistry and Biochemistry Research Vol. 11

Azomethine is one of the most important function groups that can be used in preparing many functional materials including liquid-crystalline compounds as well as polymers and semiconducting materials. This key functional group is the basis of forming a large number of rod-like and banana-shaped mesogens forming thermotropic liquid-crystalline (LC) compounds. Herein, a series of azomethine dimers 1-14 that were prepared by condensation reactions of benzaldehyde, biphenyl carboxaldehyde and 9-anthraldehyde with various aromatic diamines of varying flexibility in ethanol in the presence of tosic acid, was described. Their chemical structures were determined by Fourier transform infrared and ¹H and ¹³C nuclear magnetic resonance (NMR) spectroscopies, as well as elemental analysis. Their thermal properties were also examined by using several experimental techniques, including differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), polarising optical microscopy (POM) and variable temperature X-ray diffraction (VTXRD). IR spectra were recorded with a Shimadzu Fourier transform infrared (FTIR) analyser with neat films of azomethine compounds on KBr pellets. The ¹H and ¹³C NMR spectra of several azomethine dimers at both room temperature and high temperature, usually at 95 °C whenever possible, were recorded with a Varian nuclear magnetic resonance (VNMR) 400 spectrometer with three radio frequency (RF) channels operating at 400 and 100 MHz, respectively, in d6- DMSO using tetramethylsilane (TMS) as an internal standard, since their solubility in the chosen deuterated solvent was rather low at room temperature. Azomethine dimers 1-2, prepared from benzaldehyde and 1,9-bis(4-aminophenoxy)nonane, exhibited a monotropic, nematic liquid-crystalline (LC) phase. The majority of the azomethine dimers containing biphenyl moieties 3-8 exhibited enantiotropic, nematic LC phase on melting at relatively low temperatures since they developed typical Schlieren, threaded or marbled textures in their LC phase. They also had accessible isotropisation temperatures well below their decomposition temperatures. Azomethine dimers containing anthracene moieties 9-14 did not exhibit LC properties but exhibited polymorphism as determined by POM and VTXRD in two cases. All these azomethine dimers 1-14 had excellent thermal stability that was in the broad range of temperatures of 307–400°C depending on their degrees of aromaticity index. In future, studies could focus on designing stimuli-responsive dimers of these functional groups for advanced optoelectronic applications or incorporating them into polymer networks for high-performance materials.

 

Author (s) Details

 

Pradip K. Bhowmik
Department of Chemistry, University of Nevada at Las Vegas, 4505 Maryland Parkway, Box 454003, Las Vegas, NV 89154, USA.

 

Haesook Han
Department of Chemistry, University of Nevada at Las Vegas, 4505 Maryland Parkway, Box 454003, Las Vegas, NV 89154, USA.

 

Alexi K. Nedeltchev
Department of Chemistry, University of Nevada at Las Vegas, 4505 Maryland Parkway, Box 454003, Las Vegas, NV 89154, USA.

 

Hari D. Mandal
Department of Biology and Chemistry, Texas A&M International University, 5201 University Boulevard, Laredo, TX 78041, USA.

 

Jose A. Jimenez-Hernandez
Department of Biology and Chemistry, Texas A&M International University, 5201 University Boulevard, Laredo, TX 78041, USA.

Patrick M. McGannon
Department of Biology and Chemistry, Texas A&M International University, 5201 University Boulevard, Laredo, TX 78041, USA.

 

Leonardo Lopez
Department of Biology and Chemistry, Texas A&M International University, 5201 University Boulevard, Laredo, TX 78041, USA.

 

Shin-Woong Kang
Department of Physics, Kent State University, Kent, OH 44242, USA.

 

Satyendra Kumar
Department of Physics, Kent State University, Kent, OH 44242, USA.

 

Please see the book here:- https://doi.org/10.9734/bpi/rdcbr/v11/4228

A Comparative Investigation into the Mesomorphism of Series of Aromatic Naphthalen-2-yl 4-(Alkoxy) Benzoate and Naphthalen-1-yl 4-(Alkoxy) Benzoate Materials | Chapter 2 | New Frontiers in Physical Science Research Vol. 9

 A similar sequence of sweet ester materials' mesogenic traits are investigated. This study is aimed at equating the mesomorphic behavior of the succession described included with mesogenic fabrics we prepared and studied former. Single tail and double tail materials were combined for this comparative study. By utilizing differential flipping through calorimetry and polarized light microscopy, the chapter sequences and transition temperatures were driven. Only compounds with a sole tail and an ester connected at position 2 of the naphthalene exhibit mesogenic behaviour. Two matters (ZH 29 & ZH 32) possess a monophasic nematic step and another two materials (ZH 14 & ZH 35) display biphasic nematic and smectic (A) states. The materials with the ester fastened to naphthalene at position 1 do not display any mesogenic action. The materials accompanying two alkoxy chains bonded to the benzoate ester do not display some mesogenic behavior as well.

Author(s) Details:

Wajdi Michael Zoghaib,
Department of Chemistry, SQU, P.O. Box-36, Al-Khod, P.C.-123, Sultanate of Oman.

Carlo Carboni,
Department of Physics, SQU, P.O. Box-36, Al-Khod, , P.C.-123, Sultanate of Oman.

M. Elias Molla,
Department of Chemistry, Jahangirnagar University, Savar, Dhaka, Bangladesh.

Samiya Al-Mahrezi,
Department of Physics, SQU, P.O. Box-36, Al-Khod, , P.C.-123, Sultanate of Oman.

Turkiya Al-Shahumi,
Department of Physics, SQU, P.O. Box-36, Al-Khod, , P.C.-123, Sultanate of Oman.

Sanaa Al-Badi,
Department of Chemistry, SQU, P.O. Box-36, Al-Khod, P.C.-123, Sultanate of Oman.

Muna Al-Farsi,
Department of Chemistry, SQU, P.O. Box-36, Al-Khod, P.C.-123, Sultanate of Oman

Please see the link here: https://stm.bookpi.org/NFPSR-V9/article/view/9849