Department of Chemistry, University of California, Berkeley, CA, 94720, USA.
Chemistry. 2018 May 23;24(29):7340-7344. doi: 10.1002/chem.201801013. Epub 2018 Apr 27.
The sensing of mechanical stress in polymers is indispensable for investigating the origin and propagation of cracks that lead to material failure and for designing mechanically responsive polymers. Here the unique approaches of using the force-induced switching of aromaticity and homoaromaticity in molecular optical force sensors for the real-time measurement of mechanical forces acting in stretched polymers are suggested. The mechanical switching of aromaticity in Dewar benzene is an irreversible event, whereas the degree of π-orbital overlap in homoaromatic compounds like homotropylium can be adjusted progressively over a wide range of forces. Using computational methods, it is demonstrated that both approaches lead to significant changes in the visible part of the UV/Vis spectra of the force sensors upon application of weak forces (pN-nN). Polymers that incorporate such molecular force sensors therefore change their color well before material failure occurs.
聚合物中机械应力的传感对于研究导致材料失效的裂纹的起源和传播以及设计对机械响应的聚合物是必不可少的。这里提出了使用分子光学力传感器中芳香性和同芳香性的力诱导转换来实时测量作用在拉伸聚合物上的机械力的独特方法。Dewar 苯中的芳香性机械转换是不可逆事件，而类似于同三苯鎓的同芳香族化合物中的π轨道重叠程度可以在很宽的力范围内逐步调整。通过计算方法，证明这两种方法都导致在施加弱力（皮牛顿-纳牛顿）时，力传感器的紫外/可见光谱的可见部分发生显著变化。因此，在材料失效发生之前，掺入这种分子力传感器的聚合物就会很好地改变其颜色。
