Sequential Bending and Twisting around C-C Single Bonds by Mechanical Lifting of a Pre-Adsorbed Polymer

Bending and twisting around carbon-carbon single bonds are ubiquitous in natural and synthetic polymers. Force-induced changes were so far not measured at the single monomer level, owing to limited ways to apply local forces. We quantified down to the submolecular level the mechanical response within individual poly-pyrenylene chains upon their detachment from a gold surface with an atomic force microscope at 5 K. Computer simulations based on a dedicated force field reproduce the experimental traces and reveal symmetry-broken bent and rotated conformations of the sliding physisorbed segment besides steric hindrance of the just lifted monomer. Our study also shows that the tip-molecule bond remains intact but remarkably soft and links force variations to complex but well-defined conformational changes.