SKM 2023 – scientific programme

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 8: Responsive and Adaptive Systems

CPP 8.6: Talk

Monday, March 27, 2023, 12:15–12:30, ZEU 255

Mechanochemistry: a theoretical and experimental interplay — •Michael Walter, Wafa Maftuhin, and Pooja Bhat — Albert-Ludwigs-Universität Freiburg, Freiburg i. Br., Germany

Mechanochromic polymers are intriguing materials that allow to sense force of specimens under load. The connection between macroscopic stress and the forces acting on the molecular level is still elusive and covalently incorporated molecular mechanochromophors promise to shed light on this connection. Most mechanochromic systems rely on covalent bond scission with optically distinct *on* and *off* states. Bond rupture is induced by temperature fluctuations involving force dependent barriers. We show that these barriers are fully determined by the dissociation energy and the maximal force the potential can withstand, which allows for a re-interpretation of the Eyring-Zhurkov-Bell length Δ x^‡ and the expressions going beyond.

We furthermore present and analyse the concept of mechanochromic donor-acceptor (DA) torsional springs that allows for a contineous mapping of molecular forces to photoluminescence wavelengths. The mechanically induced deflection from equilibrium geometry of the DA spring is theoretically predicted and reveals forces of 1 nN on the molecular level. Our theoretical analysis demonstrates a thiophene ring flip as the major part of the overall mechanochromic response within a related ansa-DAD spring at forces as low as 27 pN. Such micromechanical motion gives access to sensing of tiny forces and expands both sensitivity and the force range of conformational mechanochromophores.