物理化学学报 >> 2020, Vol. 36 >> Issue (10): 1910036.doi: 10.3866/PKU.WHXB201910036

所属专题: 胶体与界面化学前沿

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基于两亲性喹喔啉的超分子凝胶:手性信号反转以及多重响应手性光学开关

汪含笑1, 徐俪菲1,2, 刘鸣华1,2,*()   

  1. 1 中国科学院化学研究所,胶体界面与化学热力学实验室,北京 100190
    2 中国科学院大学,北京 100049
  • 收稿日期:2019-10-17 录用日期:2019-11-20 发布日期:2019-11-27
  • 通讯作者: 刘鸣华 E-mail:liumh@iccas.ac.cn
  • 基金资助:
    国家自然科学基金(21890734);中国博士后科学基金(2017M620915)

Supramolecular Gel Based on Amphiphilic Quinoxaline: Chirality Inversion and Chiroptical Switch with Multiple Stimuli-Responsiveness

Hanxiao Wang1, Lifei Xu1,2, Minghua Liu1,2,*()   

  1. 1 Key Laboratory of Colloid, Interface and Chemical Thermodynamics, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, P. R. China
    2 University of Chinese Academy of Sciences, Beijing 100049, P. R. China
  • Received:2019-10-17 Accepted:2019-11-20 Published:2019-11-27
  • Contact: Minghua Liu E-mail:liumh@iccas.ac.cn
  • Supported by:
    the National Natural Science Foundation of China(21890734);China Postdoctoral Science Foundation(2017M620915)

摘要:

文设计将具有良好光学性质的喹喔啉衍生物引入L-谷氨酸基两亲分子中,得到包含较大π-共轭头基的手性功能化凝胶因子SQLG。借由多重分子间非共价相互作用的驱动,SQLG可以自组装为由纳米纤维组成的三维网络,胶凝极性从低到高的多种有机溶剂。在自组装的过程中,中心手性通过分子的不对称排列传递到超分子层面,进而在圆二色(CD)和圆偏振发光(CPL)光谱上表现出超分子手性信号。SQLG在极性溶剂和非极性溶剂中组装时采取不同的堆积模式,使两类溶剂体系中形成的组装体表现出相反的手性信号。由于喹喔啉上具有质子接受位点,对超分子凝胶进行酸化后,分子内电荷转移作用(ICT)受到明显强化,并且自组装驱动力发生改变,导致黄色凝胶坍塌为红色分散液,同时堆积模式的改变导致超分子手性信号反转,CPL信号则随着荧光猝灭而关闭,而碱的中和作用可以使体系的一系列性质变化得到恢复。因此,通过向手性两亲分子中引入酸响应性π-共轭体系,我们顺利构筑了一例具有多重外界刺激响应性的超分子手性光学开关。

关键词: 手性开关, 凝胶, 多重响应性, 喹喔啉衍生物, 超分子手性

Abstract:

The regulation of supramolecular chirality has applications in various aspects including asymmetric catalysis, chiral sensing, optical materials and smart devices. Additionally, it provides opportunities for the simulation of important activities in living organisms and the clarification of their mechanisms. Herein, we synthesized a chiral gelator SQLG (styrylquinoxalinyl L-amino glutamic diamide) containing a π-conjugated headgroup by introducing the quinoxaline-derived moiety into L-glutamic diamide-based amphiphile via two simple condensation steps. SQLG self-assembled into nanofibers through multiple intermolecular interactions, including ππ stacking, hydrogen bonding and van der Waals interaction, leading to gelation of various organic solvents ranging from nonpolar to polar ones. Chirality transfer from the chiral center to the supramolecular level was observed when organogels formed, which manifested itself in circular dichroism (CD) spectra. The organogels formed in polar solvents such as N, N-dimethylformamide (DMF) and nonpolar solvents such as toluene exhibited opposite signals of supramolecular chirality, attributed to different hydrogen bonding strengths and thus two different types of gelator stacking modes of the gelators which was confirmed by infrared spectroscopy (IR) and X-ray diffraction (XRD). Circular polarized luminescence (CPL) denotes left-handed or right-handed circularly polarized light with different intensities emitted by the chiral luminescent system, and it characterizes the chirality of the excited state, which finds potential application in fields such as 3D optical displays, optical data storage, polarization-based information encryption and bioencoding. Owing to the strong fluorescence and supramolecular chirality, the toluene gel emitted right-handed circular polarized luminescence upon excitation, while the gel formed in DMF did not exhibit CPL emission because of its relatively weak fluorescence. Furthermore, the organogels responded rapidly and distinctly to the stimulus of acid due to the proton-accepting sites in the quinoxaline skeleton. Utilizing NMR spectroscopy, we found that the two nitrogen atoms in the quinoxaline moiety could be protonated upon acidification. During the process, intramolecular charge transfer (ICT) was significantly strengthened and the driving forces of self-assembly underwent remarkable changes, resulting in the collapse of the yellow transparent organogel into a red dispersion. Meanwhile, transformation from nanofibers to nanospheres was observed using a scanning electron microscope (SEM). With change in stacking modes in the supramolecular assembly, a complete inversion of the CD signal was detected. The CPL signal was found to be switched off, which along with the other changes of the system could subsequently be recovered by neutralization of the entire system. Therefore, we constructed a chiroptical switch with multiple stimuli-responsiveness through the introduction of an acid-sensitive π-conjugated moiety into the L-glutamic diamide-based chiral amphiphile.

Key words: Chiroptical switch, Gel, Multi-responsiveness, Quinoxaline derivative, Supramolecular chirality

MSC2000: 

  • O648