A novel photo-responsive anionic surfactant with a dimethylamino-substituted azobenzene located at the end of the hydrophobic chain, 6-(4-dimethylaminoazobenzene-4′-oxy)hexanoate sodium (DAH), has been designed. Through the host–guest interaction in aqueous solution, the trans-DAH could be spontaneously included by using two native α-cyclodextrin (α-CD) molecules. The formed hydrophilic inclusion complex (DAH@2α-CD), however, could act as a gelator to induce the formation of a supramolecular hydrogel, which is driven mainly by hydrogen bonds between neighboring α-CDs and also between the carboxylate in DAH and water. Compared with common hydrogels that consist of networks with fibres or discrete polymer chains, the hydrogel formed by DAH@2α-CD was composed of periodic lamellar structures possessing good shear-thinning behavior and much swollen water layers. The more interesting point for such a hydrogel was its visible-light responsibility for gel–sol reversible phase transition. This originated from the introduction of an electron-donating group (dimethylamino) to azobenzene, which noticeably red-shifted the responsive wavelength for its trans-to-cis isomerization. It was also worth noting that the host–guest interaction between azobenzene in DAH and α-CD significantly improved the photo-transition efficiency from trans to cis forms of azobenzene, which played a critical role in the visible-light responsibility of the hydrogel. This unique visible-light-responsive behavior combined with the inherent thermo-responsive property from α-CD should make the prepared hydrogel find more potential applications in biomedical systems.

中文翻译：

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α-环糊精与偶氮苯连接的表面活性剂构成的可见光/温度双响应水凝胶

设计了一种新型的光响应型阴离子表面活性剂，其具有位于疏水链末端的二甲基氨基取代的偶氮苯6-（4-二甲基氨基偶氮苯-4'-氧）己酸钠（DAH）。通过水溶液中的主客体相互作用，反式通过使用两个天然α-环糊精（α-CD）分子可以自发包含-DAH。但是，所形成的亲水性包合物（DAH @2α-CD）可以充当胶凝剂，诱导超分子水凝胶的形成，其主要由相邻的α-CD之间以及氢原子与DAH中的羧酸盐之间的氢键驱动。与由具有纤维或不连续的聚合物链的网络组成的普通水凝胶相比，DAH @2α-CD形成的水凝胶由周期性的层状结构组成，这些结构具有良好的剪切稀化行为和许多溶胀的水层。这种水凝胶更有趣的一点是其可见光对凝胶-溶胶可逆相变的作用。这是由于在偶氮苯中引入了一个供电子基团（二甲氨基），反式-到-顺式异构化。还值得注意的是，DAH中的偶氮苯与α-CD之间的主体-客体相互作用显着提高了偶氮苯从反式到顺式形式的光转换效率，这在水凝胶的可见光响应中起着至关重要的作用。这种独特的可见光响应行为与α-CD固有的热响应特性相结合，应使制得的水凝胶在生物医学系统中找到更多的潜在应用。