Mapping the Extended Ground State Reactivity Landscape of a Photoswitchable Molecule at a Single Molecular Level

Photoswitchable molecules with structural flexibility can exhibit a complex ground state potential energy landscape due to the accessibility of multiple metastable states at merely low energy barriers. However, conventional bulk analytical techniques are limited in their ability to probe these metastable ground states and their relative energies. This is partially due to the difficulty of inducing changes in small molecules in their ground state, as they do not respond to external stimuli, such as mechanical force, unless they are incorporated into larger polymer networks. This hinders the understanding of ground-state reactivity and the associated dynamics. In this study, we leverage the "perturb-probe" capability of the single molecular break junction technique to explore the ground state 6π electrocyclization of a dithienylethene (DTE) derivative, a process traditionally achieved through electro- or photochromism. Our findings reveal that this reaction can also be triggered by mechanical force and an oriented electric field at the single-molecule level via ground state dynamics. We demonstrated that external perturbations could control the ground state reaction dynamics and steer the reaction trajectories away from constraints imposed by typical excited state dynamics. This strategy will thus offer access to a whole new dimension of single molecular electromechanical conversions and extend our knowledge of the ground state potential energy surface available to molecules under external force fields.