Institut für Organische Chemie, Universität Würzburg am Hubland, 97078, Würzburg, Germany.
Organisch-Chemisches Institut, Westfälische Wilhelms-Universität (WWU) Münster, Corrensstraße, 40., 48149, Münster, Germany.
Chemistry. 2020 Aug 6;26(44):10005-10013. doi: 10.1002/chem.202001566. Epub 2020 Jul 14.
Besides their widespread use in coordination chemistry, 2,2'-bipyridines are known for their ability to undergo cis-trans conformational changes in response to metal ions and acids, which has been primarily investigated at the molecular level. However, the exploitation of such conformational switching in self-assembly has remained unexplored. In this work, the use of 2,2'-bipyridines as acid-responsive conformational switches to tune supramolecular polymerization processes has been demonstrated. To achieve this goal, we have designed a bipyridine-based linear bolaamphiphile, 1, that forms ordered supramolecular polymers in aqueous media through cooperative aromatic and hydrophobic interactions. Interestingly, addition of acid (TFA) induces the monoprotonation of the 2,2'-bipyridine moiety, leading to a switch in the molecular conformation from a linear (trans) to a V-shaped (cis) state. This increase in molecular distortion along with electrostatic repulsions of the positively charged bipyridine-H units attenuate the aggregation tendency and induce a transformation from long fibers to shorter thinner fibers. Our findings may contribute to opening up new directions in molecular switches and stimuli-responsive supramolecular materials.
除了在配位化学中广泛应用外，2,2'-联吡啶还因其能够在金属离子和酸的作用下发生顺反构象变化而闻名，这主要在分子水平上进行了研究。然而，这种构象转换在自组装中的应用仍未得到探索。在这项工作中，我们展示了将 2,2'-联吡啶用作酸响应构象开关来调节超分子聚合过程。为了实现这一目标，我们设计了一种基于联吡啶的线性 bolaamphiphile1，它通过协同的芳香和疏水相互作用在水介质中形成有序的超分子聚合物。有趣的是，添加酸（TFA）会导致 2,2'-联吡啶部分的单质子化，从而使分子构象从线性（反式）转变为 V 形（顺式）状态。这种分子扭曲的增加以及带正电荷的联吡啶-H 单元的静电排斥作用，减弱了聚集倾向，并诱导从长纤维到更短更细纤维的转变。我们的发现可能为分子开关和刺激响应超分子材料开辟新的方向。
