Activation of a Copper Biscarbene Mechano-Catalyst Using Single-Molecule Force Spectroscopy Supported by Quantum Chemical Calculations.

Single-molecule force spectroscopy allows investigation of the effect of mechanical force on individual bonds. By determining the forces necessary to sufficiently activate bonds to trigger dissociation, it is possible to predict the behavior of mechanophores. Here, we measure the force necessary to activate a copper biscarbene mechano-catalyst intended for self-healing materials. By using a safety line bypassing the mechanophore, we were able to pinpoint the dissociation of the investigated bond and determine rupture forces to range from 1.6 to 2.6 nN at room temperature in dimethyl sulfoxide. The average length-increase upon rupture of the Cu-C bond due to the stretching of the safety line agrees with quantum chemical calculations, but the values exhibit an unusual scattering. We assign this scattering to the conformational flexibility of the mechanophore, which includes formation of a threaded structure and recoiling of the safety line.