Investigation on Y-shaped tri-fluoromethyl substituted quinoxalines: synthesis, optical and morphological studies
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ORIGINAL PAPER
Investigation on Y‑shaped tri‑fluoromethyl substituted quinoxalines: synthesis, optical and morphological studies Ayilam Viswanathan Rajalakshmi1 · Nallasamy Palanisami1 Received: 1 February 2020 / Accepted: 23 June 2020 © Institute of Chemistry, Slovak Academy of Sciences 2020
Abstract Y-shaped tri-fluoromethyl substituted quinoxaline derivatives 2,3-bis(4-methoxyphenyl)-6-(trifluoromethyl)quinoxaline (1) and 2,3-bis((E)-4-methoxystryryl)-6-(trifluoromethyl)quinoxaline (2) have been synthesized and characterized using various analytical and spectroscopic techniques (1H,13C, 19F NMR, FT-IR and HR-Mass). Optical properties such as absorption, emission, quantum yield, effect of solvent polarities and Aggregation Induced Emission (AIE) have been illustrated. The compound 1 exhibited negative solvatochromism and compound 2 positive solvatochromism which are in correlation with π* values by Kamlet and Taft. Compounds 1 and 2 showed large Stoke’s shifts attributed to more polar excited state of the compounds as compared to that of polar ground state, due to the presence of electron withdrawing trifluoromethyl group. Both the compounds displayed fluorescence in solid state and AIE state due to the restricted intramolecular rotation. The compounds 1 and 2 exhibited low quantum yields because of ICT (Intramolecular charge transfer) attributed to the presence of electron-donating methoxy phenyl unit and an electron-withdrawing quinoxaline unit. AIE exhibited by both the compounds in THF/water mixture were due to the formation of nano-aggregates, it is further characterised by DLS and determined the particle size to be 196.8 nm for compound 1 and 197.3 nm for compound 2. Compound 1 appeared as ice flakes and compound 2 as a cluster consisting of various micro crystals like projections in the images determined by scanning electron microscope (SEM).
Electronic supplementary material The online version of this article (https://doi.org/10.1007/s11696-020-01266-3) contains supplementary material, which is available to authorized users. * Nallasamy Palanisami [email protected] 1
Department of Chemistry, School of Advanced Sciences, Vellore Institute of Technology, Vellore, Tamil Nadu 632014, India
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Chemical Papers
Graphic abstract
Keywords Quinoxaline · Fluorescence · Quantum yield · AIE
Introduction Quinoxaline and its derivatives have been extensively synthesized for the development of industrially useful elements like dyes, optical, electro-luminescent materials and were also well-established in the field of biological sciences (Neri et al. 2020; Achelle et al. 2013; Montana et al. 2019; Pereira et al. 2015; Tariq et al. 2018; Neri et al. 2018). The uniqueness of compounds containing fluorine was attributed to the facts that fluorine is the most electronegative element in the periodic table, it is the most reactive halogen and also fluorine is the smallest substituent other than hydrogen or hydrogen’s isotopes (Dolbier 2005). The trifluoromethyl substituted quinoxali
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