Barber Ross W, Robb Maxwell J
Division of Chemistry and Chemical Engineering, California Institute of Technology Pasadena California 91125 USA
Chem Sci. 2021 Jul 22;12(35):11703-11709. doi: 10.1039/d1sc02890a. eCollection 2021 Sep 15.
Molecular force probes conveniently report on mechanical stress and/or strain in polymers through straightforward visual cues. Unlike conventional mechanochromic mechanophores, the mechanically gated photoswitching strategy decouples mechanochemical activation from the ultimate chromogenic response, enabling the mechanical history of a material to be recorded and read on-demand using light. Here we report a completely redesigned, highly modular mechanophore platform for mechanically gated photoswitching that offers a robust, accessible synthesis and late stage diversification through Pd-catalyzed cross-coupling reactions to precisely tune the photophysical properties of the masked diarylethene (DAE) photoswitch. Using solution-phase ultrasonication, the reactivity of a small library of functionally diverse mechanophores is demonstrated to be exceptionally selective, producing a chromogenic response under UV irradiation only after mechanochemical activation, revealing colored DAE isomers with absorption spectra that span the visible region of the electromagnetic spectrum. Notably, mechanically gated photoswitching is successfully translated to solid polymeric materials for the first time, demonstrating the potential of the masked diarylethene mechanophore for a variety of applications in force-responsive polymeric materials.
分子力探针通过直观的视觉线索方便地报告聚合物中的机械应力和/或应变。与传统的机械变色机械发色团不同，机械门控光开关策略将机械化学活化与最终的显色响应解耦，使得材料的机械历史能够通过光被记录并按需读取。在此，我们报道了一个完全重新设计的、高度模块化的用于机械门控光开关的机械发色团平台，该平台通过钯催化的交叉偶联反应提供了一种稳健、易于实现的合成方法以及后期多样化功能，从而精确调节掩蔽二芳基乙烯（DAE）光开关的光物理性质。利用溶液相超声处理，证明了一小批功能多样的机械发色团的反应具有极高的选择性，仅在机械化学活化后在紫外线照射下产生显色响应，揭示出吸收光谱跨越电磁光谱可见光区域的有色DAE异构体。值得注意的是，机械门控光开关首次成功地应用于固态聚合物材料，证明了掩蔽二芳基乙烯机械发色团在力响应聚合物材料中的多种应用潜力。
