Quantum Chemical Investigation of the Influence of Oriented External Electric Fields on the Mechanical Properties of Mechanophores in Polymers

定向外电场（OEEF）通过在过渡态中大力支持两性离子共振结构，已被用于催化许多反应。此外，在OEEF分子的几何形状和化学键的离解能的变化已被报道。该项目的假设是，材料的机械性能，这是快速发展的机械化学领域的焦点，可以通过OEEF进行调整。特别是，如果电场的强度及其与分子的相对取向选择得当，将表明OEEF会降低机械载体的断裂力，机械载体即聚合物的分子亚基，其通过显著的结构变化响应机械力。因为在实验中很难控制电场和分子的相对取向。外力解释包括（EFEI）方法将用于计算机械变形分子的断裂力。分子的受力支架将通过能量分布判断（JEDI）分析来确定，该分析允许合理优化所研究的分子在OEEF存在下对力的响应。将进行仔细的基准测试，以确定一种计算方法，该方法允许可靠但成本-有效地计算了OEEF中不同分子的断裂力。随后，在不同强度和方向的电场存在下，在各种已建立的机械化学反应中的分子的断裂力将被计算。对温度或聚合物链的化学组成等外部效应的研究完成了工作计划，为实验验证铺平了道路。OEEF与机械化学耦合的潜在应用是有趣的：首先，电场和机械力的影响允许机械响应的双重切换，即断裂力的选择性增加或减少，通过调整电场的强度和方向。这在机械致变色材料中特别有趣，当施加特征阈值力时，机械致变色材料显示颜色变化。其次，许多自修复聚合物依赖于断裂诱导的自由基的形成和相邻链的后续重组。然而，OEEF已被证明通常切换均裂异裂键断裂事件。因此，通过结合这两种效应，可以选择性地允许或禁止聚合物的自修复。

Oriented external electric fields (OEEFs) have been used to catalyze a number of reactions by energetically favoring zwitterionic resonance structures in the transition state. Moreover, changes in geometries and dissociation energies of chemical bonds have been reported for molecules in OEEFs. The hypothesis of the proposed project is that the mechanical properties of materials, which are the focus of the rapidly growing field of mechanochemistry, can be tuned by OEEFs. In particular, it shall be shown that OEEFs decrease the rupture force of a mechanophore, i.e. a molecular subunit of a polymer that responds to mechanical forces via significant structural changes, if the strength of the electric field and its relative orientation to the molecule is chosen appropriately.In this project, quantum chemical methods will be used, since it is extremely difficult to control the relative orientation of the electric field and the molecule in an experiment. The External Force is Explicitly Included (EFEI) method will be used to calculate the rupture forces of mechanically deformed molecules. The force-bearing scaffold of the molecule will be identified with the Judgement of Energy DIstribution (JEDI) analysis, which allows the rational optimization of the response of the investigated molecules to forces in the presence of OEEFs.In the beginning of the project, a careful benchmark will be carried out to identify a computational method that allows the reliable yet cost-efficient calculation of the rupture forces of diverse molecules in OEEFs. Subsequently, the rupture forces of molecules in various established mechanochemical reactions will be calculated in the presence of electric fields of different strengths and orientations. The investigation of external effects like temperature or the chemical composition of the polymer chain complete the work program, paving the way for experimental validation.The potential applications of the coupling of OEEFs with mechanochemistry are intriguing: Firstly, the influence of both electric fields and mechanical forces allows a dual switching of the mechanical response, i.e. a selective increase or decrease of the rupture forces, by tuning the strength and orientation of the electric field. This is particularly interesting in mechanochromic materials, which show a color change when a characteristic threshold force is applied. Secondly, many self-healing polymers rely on the rupture-induced formation of radicals and the subsequent recombination of neighboring strands. However, OEEFs have been demonstrated to switch typically homolytic to heterolytic bond rupture events. Hence, by combining the two effects the self-healing of polymers can be selectively allowed or forbidden.