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

Bis(4-alkoxyphenyl) Viologen Bis(triflimide) Salts: Synthesis, Thermotropic Liquid-crystalline and Light-emitting Properties | Chapter 3 | Current Topics on Chemistry and Biochemistry Vol. 2

 Extended viologens with various organic counterions are a type of ionic liquid crystal that combines the characteristics of ionic liquids and liquid crystals. We provide a set of extended viologens with similar features in this paper. The metathesis reaction of respective bis(4-alkoxyphenyl) viologen dichloride salts, which were prepared from the reaction of Zincke salt with the corresponding 4-n-alkoxyanilines, with lithium triflimide in methanol, yielded a series of bis(4-alkoxyphenyl) viologen bis(triflimide) salts with alkoxy chains of various lengths. Nuclear Magnetic Resonance spectra for 1H and 13C, as well as elemental analyses, were used to determine their chemical structures. Differential scanning calorimetry, polarised optical microscopy, and variable temperature X-ray diffraction were used to investigate their thermotropic liquid-crystalline (LC) characteristics. Crystal-to-liquid transitions were seen in salts with short alkoxy chains. Both crystal-to-SmA and SmA-to-isotropic transitions, Tms and Tis, were seen in salts of intermediate length alkoxy chains. Those with long alkoxy chains had lower Tms, which allowed them to form SmA phases that lasted until decomposition at high temperatures. In the temperature range of 330-370 C, they all showed outstanding thermal stabilities, as expected. In addition, their light-emitting capabilities in methanol were taken into account.

Author(s) Details:

Pradip K. Bhowmik,
Department of Chemistry and Biochemistry, University of Nevada Las Vegas, 4505 S. Maryland Parkway, Box 454003, Las Vegas, NV 89154-4003, USA.

Mohammed Kareem M. Al-Karawi,
Department of Chemistry and Biochemistry, University of Nevada Las Vegas, 4505 S. Maryland Parkway, Box 454003, Las Vegas, NV 89154-4003, USA.

Shane T. Killarney,
Department of Chemistry and Biochemistry, University of Nevada Las Vegas, 4505 S. Maryland Parkway, Box 454003, Las Vegas, NV 89154-4003, USA.

Erenz J. Dizon,
Department of Chemistry and Biochemistry, University of Nevada Las Vegas, 4505 S. Maryland Parkway, Box 454003, Las Vegas, NV 89154-4003, USA.

Anthony Chang,
Department of Chemistry and Biochemistry, University of Nevada Las Vegas, 4505 S. Maryland Parkway, Box 454003, Las Vegas, NV 89154-4003, USA.

Jongin Kim,
Department of Chemistry and Biochemistry, University of Nevada Las Vegas, 4505 S. Maryland Parkway, Box 454003, Las Vegas, NV 89154-4003, USA.

Si L. Chen,
Department of Chemistry and Biochemistry, University of Nevada Las Vegas, 4505 S. Maryland Parkway, Box 454003, Las Vegas, NV 89154-4003, USA.

Ronald Carlo G. Principe,
Department of Chemistry and Biochemistry, University of Nevada Las Vegas, 4505 S. Maryland Parkway, Box 454003, Las Vegas, NV 89154-4003, USA.

Andy Ho,
Department of Chemistry and Biochemistry, University of Nevada Las Vegas, 4505 S. Maryland Parkway, Box 454003, Las Vegas, NV 89154-4003, USA.

Haesook Han,
Department of Chemistry and Biochemistry, University of Nevada Las Vegas, 4505 S. Maryland Parkway, Box 454003, Las Vegas, NV 89154-4003, USA.

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

Raymond G. Cortez,
Department of Biology and Chemistry, Texas A & M International University, 5201 University Blvd., Laredo, TX 78041, USA.

Bryan Gutierrez,
Department of Biology and Chemistry, Texas A & M International University, 5201 University Blvd., Laredo, TX 78041, USA.

Klarissa Mendez,
Department of Biology and Chemistry, Texas A & M International University, 5201 University Blvd., Laredo, TX 78041, USA.

Lewis Sharpnack,
Department of Earth Science, 1006 Webb Hall, University of California, Santa Barbara, CA 93106, USA.

Dena M. Agra-Kooijman,
Advanced Materials and Liquid Crystal Institute, Kent State University, Kent, OH 44242, USA.

Michael R. Fisch,
College of Aeronautics and Engineering, Kent State University, Kent, OH 44242, USA.

Satyendra Kumar,
Division of Research, University at Albany, Albany, NY 12222, USA.

Please see the link here: https://stm.bookpi.org/CTCB-V2/article/view/7130