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Polymer Mechanochromism from Force-Tuned Excited-State Intramolecular Proton Transfer
Journal of the American Chemical Society ( IF 14.4 ) Pub Date : 2022-05-26 , DOI: 10.1021/jacs.2c03056
Huan Hu 1 , Xin Cheng 1 , Zhimin Ma 2 , Rint P Sijbesma 3 , Zhiyong Ma 1, 4
Journal of the American Chemical Society ( IF 14.4 ) Pub Date : 2022-05-26 , DOI: 10.1021/jacs.2c03056
Huan Hu 1 , Xin Cheng 1 , Zhimin Ma 2 , Rint P Sijbesma 3 , Zhiyong Ma 1, 4
Affiliation
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Real-time monitoring of strain/stress in polymers is a big challenge to date. Herein, we for the first time report an ESIPT (excited-state intramolecular proton transfer)-based mechanochromic mechanophore (MM). The synthesis of target MM PhMz-4OH [(2-hydroxyphenyl)benzimidazole with four aliphatic hydroxyls] is quite facile. PhMz-4OH possesses characteristic dual emissions, and its ESIPT activity is greatly affected by steric hindrance. Then, PhMz-4OH was covalently linked into polyurethane chains (PhMz-4OH@PU). Upon stretching, the PhMz-4OH@PU films showed fluorescence color change and spectral variation with the increase in enol emission and blueshift of keto emission due to the force-induced torsion of the dihedral angle between the proton donor and the proton acceptor. The PhMz-4OH@PU films with high mechanophore concentrations (>0.36 mol %) might undergo a two-stage force-responsive process, including torsion of the dihedral angle via force-induced disaggregation and direct chain-transduced force-induced torsion of the dihedral angle. The intensity ratio of enol emission to keto emission (IE/IK) shows a quantitative correlation with elongation, and real-time strain sensing is achieved. PhMz-4OH is a successful type II MM (without covalent bond scission) and displays high sensitivity and excellent reversibility to stress. Two control structures PhMz-NH2 and PhMz-2OH were also embedded into PU but no spectral or color changes were detected, further confirming that mechanochromism of PhMz-4OH@PU films arises from the chain-transduced force. Density function theory (DFT) calculation was performed to study the force-tuned ESIPT process theoretically and rationalize the experimental results. This study might lay the foundation for real-time stress/strain sensing in practical applications.
中文翻译：
力调谐激发态分子内质子转移的聚合物机械变色
迄今为止，实时监测聚合物中的应变/应力是一个巨大的挑战。在此，我们首次报道了一种基于 ESIPT（激发态分子内质子转移）的机械变色机械载体（MM）。目标MM PhMz-4OH [(2-羟基苯基)苯并咪唑与四个脂肪族羟基]的合成非常容易。PhMz-4OH具有双重发射特性，其ESIPT活性受空间位阻影响较大。然后，PhMz-4OH 共价连接成聚氨酯链（PhMz-4OH@PU）。在拉伸时，由于质子供体和质子受体之间的二面角的力诱导扭转，随着烯醇发射和酮发射蓝移的增加，PhMz-4OH@PU薄膜显示出荧光颜色变化和光谱变化。PhMz-4OH@PU 薄膜具有高机械载体浓度 (>0. 36 mol %) 可能经历一个两阶段的力响应过程，包括通过力诱导的解聚和直接链转换力诱导的二面角扭转的二面角扭转。烯醇排放与酮排放的强度比（I E / I K ) 显示出与伸长率的定量相关性，并实现了实时应变传感。PhMz-4OH 是一种成功的 II 型 MM（无共价键断裂），具有高灵敏度和出色的应力可逆性。两种控制结构 PhMz-NH 2和 PhMz-2OH 也嵌入到 PU 中，但没有检测到光谱或颜色变化，进一步证实了 PhMz-4OH@PU 薄膜的机械致变色是由链转力引起的。进行了密度函数理论（DFT）计算，从理论上研究了力调谐的 ESIPT 过程，并使实验结果合理化。这项研究可能为实际应用中的实时应力/应变传感奠定基础。
更新日期：2022-05-26
中文翻译：
力调谐激发态分子内质子转移的聚合物机械变色
迄今为止，实时监测聚合物中的应变/应力是一个巨大的挑战。在此，我们首次报道了一种基于 ESIPT（激发态分子内质子转移）的机械变色机械载体（MM）。目标MM PhMz-4OH [(2-羟基苯基)苯并咪唑与四个脂肪族羟基]的合成非常容易。PhMz-4OH具有双重发射特性，其ESIPT活性受空间位阻影响较大。然后，PhMz-4OH 共价连接成聚氨酯链（PhMz-4OH@PU）。在拉伸时，由于质子供体和质子受体之间的二面角的力诱导扭转，随着烯醇发射和酮发射蓝移的增加，PhMz-4OH@PU薄膜显示出荧光颜色变化和光谱变化。PhMz-4OH@PU 薄膜具有高机械载体浓度 (>0. 36 mol %) 可能经历一个两阶段的力响应过程，包括通过力诱导的解聚和直接链转换力诱导的二面角扭转的二面角扭转。烯醇排放与酮排放的强度比（I E / I K ) 显示出与伸长率的定量相关性，并实现了实时应变传感。PhMz-4OH 是一种成功的 II 型 MM（无共价键断裂），具有高灵敏度和出色的应力可逆性。两种控制结构 PhMz-NH 2和 PhMz-2OH 也嵌入到 PU 中，但没有检测到光谱或颜色变化，进一步证实了 PhMz-4OH@PU 薄膜的机械致变色是由链转力引起的。进行了密度函数理论（DFT）计算，从理论上研究了力调谐的 ESIPT 过程，并使实验结果合理化。这项研究可能为实际应用中的实时应力/应变传感奠定基础。
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