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Distinct Tetracyanoquinodimethane Derivatives: Enhanced Fluorescence in Solutions and Unprecedented Cation Recognition in the Solid State
ACS Omega ( IF 4.1 ) Pub Date : 2021-01-22 , DOI: 10.1021/acsomega.0c05486
Anwarhussaini Syed 1 , Himabindu Battula 1 , Sabyashachi Mishra 2 , Subbalakshmi Jayanty 1
Affiliation  

Tetracyanoquinodimethane (TCNQ) is known to react with various amines to generate substituted TCNQ derivatives with remarkable optical and nonlinear optical characteristics. The choice of amine plays a crucial role in the outcome of molecular material attributes. Especially, mono/di-substituted TCNQ’s possessing strong fluorescence in solutions than solids are deficient. Furthermore, cation recognition in the solid-state TCNQ derivatives is yet undetermined. In this article, we present solution-enhanced fluorescence and exclusive solid-state recognition of K+ ion achieved through the selection of 4-(4-aminophenyl)morpholin-3-one (APM) having considerable π-conjugation and carbonyl (C═O) functionality, particularly in the ring. TCNQ when reacted with APM, in a single-step reaction, resulted in two well-defined distinct compounds, namely, 7,7-bis(4-(4-aminophenyl)morpholin-3-ono)dicyanoquinodimethane (BAPMDQ [1], yellow) and 7,7,8-(4-(4-aminophenyl)morpholin-3-ono)tricyanoquinodimethane (APMTQ [2], red), with increased fluorescence intensity in solutions than their solids. Crystal structure investigation revealed extensive C–H−π interactions and strong H-bonding in [1], whereas moderate to weak interactions in [2]. Surprisingly, simple mechanical grinding during KBr pellet preparation with [1, 2] triggered unidentified cation recognition with a profound color change (in ∼1 min) detected by the naked eye, accompanied by a drastic enhancement of fluorescence, proposed due to the presence of carbonyl functionality, noncovalent intermolecular interactions, and molecular assemblies in [1, 2] solids. Cation recognition was also noted with various other salts as well (KCl, KI, KSCN, NH4Cl, NH4Br, etc.). Currently, the recognition mechanism of K+ ion in [1, 2] is demonstrated by the strong electrostatic interaction of K+ ion with CO and simultaneously cation−π interaction of K+ with the phenyl ring of APM, supported by experimental and computational studies. Computational analysis also revealed that a strong cation−π interaction occurred between the K+ ion and the phenyl ring (APM) in [2] than in [1] (ΔGbinding calculated as ∼16.3 and ∼25.2 kcal mol–1 for [1] and [2], respectively) providing additional binding free energy. Thus, both electrostatic and cation−π interactions lead to the recognition. Scanning electron microscopy of drop-cast films showed microcrystalline “roses” in [1] and micro/nano “aggregates” in [2]. Optical band gap (∼3.565 eV) indicated [1, 2] as wide-band-gap materials. The current study demonstrates fascinating novel products obtained by single-pot reaction, resulting in contrasting optical properties in solutions and experiencing cation recognition capability exclusively in the solid state.

中文翻译:

独特的四甲基氨基喹啉甲烷衍生物:溶液中增强的荧光和固态中前所未有的阳离子识别

已知季戊四醇二醌甲烷(TCNQ)与各种胺反应生成具有显着光学和非线性光学特性的取代TCNQ衍生物。胺的选择在分子材料属性的结果中起着至关重要的作用。特别地,在溶液中比固体具有强荧光的单/二取代的TCNQ不足。此外,固态TCNQ衍生物中的阳离子识别尚未确定。在本文中,我们介绍了溶液增强的荧光和K +的独家固态识别通过选择具有相当大的π-共轭和羰基(C = O)官能度的4-(4-氨基苯基)吗啉-3-酮(APM)获得的离子,特别是在环中。TCNQ与APM反应,在一步反应中产生了两种定义明确的独特化合物,即7,7-双(4-(4-(氨基苯基)吗啉-3-ono)二氰基喹二甲烷(BAPMDQ [ 1 ],黄色)和7,7,8-(4-(4-氨基苯基)吗啉-3-ono)三氰基喹甲烷(APMTQ [ 2 ],红色),溶液中的荧光强度高于其固体。晶体结构研究揭示广泛C-H-π相互作用和[强氢键1 ],而中等至弱相互作用在[ 2]。令人惊讶地,用KBr压片制备过程简单机械研磨[ 12 ]触发了深刻的颜色变化(〜1分钟)未识别阳离子识别通过肉眼检测到,伴随着剧烈的增强荧光的,由于提出的存在羰基官能团,非共价的分子间相互作用,并且在[分子组件12 ]的固体。也注意到各种其他盐(KCl,KI,KSCN,NH 4 Cl,NH 4 Br等)的阳离子识别。目前,K的识别机制+离子在[ 12 ]是由K的强静电相互作用证实通过实验和计算研究的支持,CO的+离子以及K +与APM的苯环同时发生阳离子-π相互作用。计算分析还表明,K个之间发生强阳离子-π相互作用+在[离子和苯环(APM)2 ]比[ 1 ](Δ ģ结合计算为~16.3和~25.2千卡摩尔-1为[ 12分别提供额外的结合自由能。因此,静电和阳离子-π相互作用都导致识别。滴铸膜的扫描电子显微镜显示微晶“玫瑰”在[ 1]和[ 2 ]中的微米/纳米“聚集” 。光学带隙(~3.565 eV)的指示[ 12 ]作为宽带隙材料。当前的研究表明,通过单罐反应获得的新颖产品令人着迷,从而使溶液中的光学性能形成对比,并仅在固态下具有阳离子识别能力。
更新日期:2021-02-02
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