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

• Applicant: Professor Dr. Tim Neudecker
• Subject Area: Theoretical Chemistry: Electronic Structure, Dynamics, Simulation
• Term: since 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 441071849

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.

• DFG Programme: Research Grants