Impact of Polymer Matrix on Polymer Mechanochromism from Excited State Intramolecular Proton Transfer†,Chinese Journal of Chemistry

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Impact of Polymer Matrix on Polymer Mechanochromism from Excited State Intramolecular Proton Transfer†
Chinese Journal of Chemistry ( IF 5.5 ) Pub Date : 2023-11-13 , DOI: 10.1002/cjoc.202300451
Yu Wu ₁ , Xin Cheng ₁ , Huan Hu ₁ , Shui Hu ₂ , Zhimin Ma ₃ , Zhiyong Ma ₁

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Mechanochromic polymers based on non-covalent changes have attracted much attention recently. Herein, we report the impact of inter/intramolecular hydrogen bonds on polymer mechanochromism from the excited state intramolecular proton transfer (ESIPT) process. PhMz-NH₂-OH and PhMz=2A are designed and obtained by simple and high-yield synthesis, and are connected into polyurethane and poly(methyl acrylate-co-2-ethylhexyl acrylate), respectively. In the initial state, the PhMz-NH₂-OH@PU sample shows blue fluorescence from the excited enol form (E*) excitons, owing to intermolecular hydrogen bonds that interrupt the ESIPT reactions but the PhMz=2A@PMA-2-EA sample expresses cyan fluorescence belonging to the excited keto form (K*) emission, implying that the intramolecular hydrogen bonds matter. Furthermore, under stretching, external force can tune the emission of the PhMz=2A@PMA-2-EA sample from K* to E* state. Though external force can putatively still promote a bond rotation, ESIPT reactions remain equivalently interrupted in both the relaxed and stressed states in a hydrogen-bond donating environment. DFT calculation confirms the force-induced increase in dihedral angle for the transition of ESIPT-on/off. Thus, PhMz-NH₂-OH@PU and PhMz=2A@PMA-2-EA showed disparate initial ESIPT states and further different responses/sensitivity to force. This study reports a novel and efficient strategy for enriching mechanochromic investigation and extending the applications of ESIPT reactions.

中文翻译：

聚合物基质对激发态分子内质子转移聚合物力致变色的影响†

基于非共价变化的力致变色聚合物最近引起了广泛关注。在此，我们报告了激发态分子内质子转移（ESIPT）过程中分子间/分子内氢键对聚合物力致变色的影响。通过简单、高产率的合成设计并获得了PhMz-NH ₂ -OH和PhMz=2A，并分别连接成聚氨酯和聚(丙烯酸甲酯-共聚丙烯酸-2-乙基己酯)。在初始状态下，PhMz-NH ₂ -OH@PU 样品显示来自激发的烯醇型 (E*) 激子的蓝色荧光，这是由于分子间氢键中断了 ESIPT 反应，但 PhMz=2A@PMA-2-EA样品发出属于激发酮形式 (K*) 发射的青色荧光，这表明分子内氢键很重要。此外，在拉伸下，外力可以将PhMz=2A@PMA-2-EA样品的发射从K*状态调整到E*状态。尽管外力仍可推定促进键旋转，但在氢键供给环境中的松弛状态和受压状态下，ESIPT 反应仍然被同等地中断。DFT 计算证实了 ESIPT 开/关转变时力引起的二面角增加。因此，PhMz-NH ₂ -OH@PU和PhMz=2A@PMA-2-EA表现出不同的初始ESIPT状态以及对力的进一步不同的响应/敏感性。本研究报告了一种新颖有效的策略，用于丰富力致变色研究并扩展 ESIPT 反应的应用。

更新日期：2023-11-13

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