Experimental Observation of Induced Thermoluminescence Nematic Liquid Crystals for Optoelectronic Applications
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Experimental Observation of Induced Thermoluminescence Nematic Liquid Crystals for Optoelectronic Applications A. Ramya and V. N. Vijayakumar∗ Department of Physics, Condensed Matter Research Laboratory (CMRL), Bannari Amman Institute of Technology, Sathyamangalam 638401, Tamil Nadu, India
K. Rajakumar Nanotechnology Education & Research Centre, South Ural State University, Chelyabinsk 454080, Russia
V. Balasubramanian Department of Science, Sona College of Technology, Salem 636005, Tamil Nadu, India
S. Balamuralikrishnan Department of Physics (DDE), Annamalai University, Annamalainagar, 608002, Tamil Nadu, India (Received 15 May 2020; revised 10 July 2020; accepted 5 August 2020) A new class of intermolecular hydrogen bonded liquid-crystal complex (HBLC) was designed and synthesized from non-mesogenic benzylmalonic acid (BMA) and mesogenic 4n-pentyloxybenzoic acid (5OBA). Intermolecular hydrogen bonds (H-bond) and vibrational functional groups were characterized by using Fourier transform-infrared spectroscopy (FTIR). Textural characterizations and the corresponding transition temperature along with enthalpy values were observed using polarizing optical microscopy (POM) and differential scanning calorimetry (DSC). The optical absorption and emission bandgap energies were calculated by using ultraviolet-visible (UV-vis) and photoluminescence (PL) spectra. The phase transition temperature, thermal stability factor, and thermal span width were calculated and their impact on the liquid crystal properties are discussed. An interesting feature of the BMA+5OBA HBLC complex was the observation of schlieren textures, and the induced thermoluminescence with parachromic variation in the nematic phase is an alternative tool for the manufacture of opto-electronic devices. Keywords: POM, DSC, Schlieren texture, Thermoluminescence, Parachromic variation DOI: 10.3938/jkps.77.1172
I. INTRODUCTION Most liquid crystal (LC) researchers have focused on the synthesis of the Hydrogen-bonded liquid crystal (HBLC) complex from soft materials. This material which has a non-covalent interaction offers a significant mesomorphic behavior in the LC complex [1–6]. The non-covalent interaction in the carboxylic acid group has been revealed to have different kinds of physico-chemical properties [7]. HBLC materials are synthesized by choosing an appropriate mixture of proton donor and acceptor groups. This offers a mesomorphic property that depends on the strength of the H-bond and the directionality [8,9]. The aromatic group and the pi conjugate columnar mesogenic material exhibit a luminescence behavior that is due to its resonance stability and molecular ∗ E-mail:
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pISSN:0374-4884/eISSN:1976-8524
structure [10,11]. The molecules are self-organized within a strong π-conjugation system due to the H-bonds and thus induces thermoluminescence in the mesogenic material [12]. Nowadays, luminescent LC material have been fascinating and have gained attention in optoelectronic applications. Luminescent materials exhibit dynamic respon
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