Increasing the applicability of mechanophores Sourabh Kumar 1 and Tim Neudecker 123
1 University of Bremen, Institute for Physical and Theoretical Chemistry, Germany, 2 Bremen Center for Computational Materials Science, University of Bremen, Germany, 3 MAPEX Center for Materials and Processes, University of Bremen, Germany Under mechanical stress, polymers respond in the form of various useful effects 1 , for example, change in color of materials under tensile stress or self-healing. Mechanophores, small molecular units, typically incorporated into the backbone of the polymers, allow polymers to show such interesting effects and are used to design smart materials. The advantage of the mechanophore is that it competes with the unspecific scission in the polymer chain but also brings the disadvantage of a specific amount of force for activation of a particular mechanophore. 2 To overcome this limitation, we explored the role of linkers which are joining the mechanophores with the polymer backbone. Using quantum chemical methods, it is demonstrated that the activation forces of three mechanophores (Dewar benzene, benzocyclobutene and gem-dichlorocyclopropane) can be adjusted over a range of almost 300% by modifying the chemical composition of the linker. Using these findings it is straightforward to either significantly enhance or reduce the activation rate of mechanophores in stress- responsive materials, depending on the desired use case. 3 Another interesting feature that can be used to increase the applicability of these mechanophore incorporated functional materials is the reversibility. Using computational methods, we here, present a general method for restoring a force-activated mechanophore to its deactivated form by using hydrostatic pressure. We use the spiropyran-merocyanine (SP-MC) interconversion to show that repeated activation of the SP mechanophore and deactivation of MC can be achieved by alternating mechanical stretching and hydrostatic compression, respectively. 4 To focus on more realistic modelling of the polymer environment, we are working to develop a multi- scale model of mechanophores embedded in the polymer matrix. References
1. T. Stauch, A. Dreuw, Chem. Rev., 2016, 116 , 14137–14180. 2. Y. Tian, et al., J. Am. Chem. Soc., 2020, 142 , 18687–18697. 3. S. Kumar, T. Stauch, RSC Adv., 2021, 11 , 7391–7396. 4. S. Kumar, F. Zeller, T. Stauch, J. Phys. Chem. Lett., 2021, 12 , 9470−9474.
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© The Author(s), 2022
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