对氟离子呈现状态和比色响应的有机凝胶的研究进展

Advances in Organogels with State and Colorimetric Response to Fluoride

氟离子刺激响应的有机凝胶因子通过氢键识别或复合氟离子,使紫外吸收波长红移而发生颜色变化,实现比色响应;同时破坏凝胶形成的主要驱动力,诱导凝胶-溶胶转变,实现状态响应。能够响应外界氟离子刺激的有机凝胶在氟离子检测方面表现出明显的优势,具有方便快捷的肉眼检测效果,并且可以实现氟离子对准固体的检测,因此,具有氟离子刺激响应性的小分子有机凝胶受到人们越来越多的关注。文献报道较多的氟离子响应有机凝胶只能对氟离子刺激呈现状态响应,即氟离子加入能够诱导凝胶-溶胶转变,却不能诱导体系颜色变化;或者只能对氟离子刺激呈现比色响应,即氟离子加入能够诱导体系颜色变化,却不能诱导凝胶-溶胶转变。而对氟离子具有双重响应性的有机凝胶在氟离子探测方面具有更明显的优势,可以同时表现出肉眼可见的状态响应(凝胶-溶胶)和比色响应(颜色变化)。目前为止,对氟离子具有双重响应性的有机凝胶已经有一些报道。研究较多的是氢键型有机凝胶,凝胶因子中含有酰胺、酰腙、脲、酰肼等官能团,分子间氢键相互作用是凝胶形成的主要驱动力。由于氟离子有很强的电负性,能够与凝胶因子上的氢质子复合或发生去质子化,从而导致凝胶的破坏或颜色变化。因此,氟离子的响应机理基本上都是氢键相互作用和去质子化过程。但是凝胶因子与氟离子具体的响应过程千差万别,不仅与凝胶因子提供的氢键类型有直接关系,还与凝胶因子中的共轭基团、取代基性质和位置等有关。因此有必要对氟离子响应有机凝胶进行系统总结。基于此,结合本课题组近期对氟离子响应有机凝胶的研究结果,对近年来文献报道的有关氟离子刺激响应的有机凝胶体系,重点是近年来文献报道的对氟离子同时表现出肉眼可见的状态和比色响应的有机凝胶体系进行综述,以期为新型氟离子响应有机凝胶体系的分子设计提供一些参考。

The fluoride-responsive organogels,the recognization and combination of the gelators with fluoride anions through hydrogen bonding will induce the red shift of UV absorption wavelength and then the change of color,realizing the colorimetric response.At the same time,the main driving force of gel formation is destroyed,and the gel-sol transition is induced to achieve the state response.The fluoride-responsive organogels capable of responding to external fluoride anions show obvious advantages in fluoride anion detection,because the convenient and quick detection by naked eyes,and the detection of fluoride anions to quasi solid can be realized.Therefore,the fluoride-responsive organogels have attracted more and more attention.It has been reported that many fluoride-responsive organogels only hold single response mode to fluoride anions.Specifically speaking,the addition of fluoride anions can only induce the gel-sol transition and fail to induce color change of the system,or it only bring about color change of the system rather than the gel-sol transition.Accordingly,the fluoride-responsive organogels capable of both response modes,namely presenting gel-sol transition and color changes,to fluoride anions are superior in fluoride detection.Up to now,the researches on fluoride-responsive organogels with dual response modes to fluoride anions have been reported.Most researches focus on organogels based on intermolecular hydrogen bonding,their gelators contain functional groups like amide,hydrazone,urea,hydrazine,and so forth,and the main driving force for the formation of organogels lies in intermolecular hydrogen bonding interaction.Thanks to the strong electronegativity of fluoride anions,the deprotonation of gelators will take place,resulting in the destruction or color change of the organogels.Consequently,the response mechanism of fluorine ions primarily consists of hydrogen bonding interaction and deprotonation process.However,the responsive process of fluoride anions and gelators are quite different in various systems,which is not only directly related to the type of hydrogen bond provided by the gelators,but also affected by the conjugated groups,the nature and location of the substituents.Therefore,a comprehensive summary concerning the fluorine-responsive organogels is necessary.Based on this,combining with the recent research results of our group on fluoride-responsive organogels,we summarize the fluoride-responsive organogels reported in the literatures in recent years,especially the organogel systems which showed both reversible color change and gel-sol transition by fluoride anions stimuli,for the sake of providing some references for molecular design of the organogels with fluoride anions response.