Nanoscale Manipulation of Single-Molecule Conformational Transition through Vibrational Excitation.

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Controlling molecular actions on demand is a critical step toward developing single-molecule functional devices. Such control can be achieved by manipulating the interactions between individual molecules and their nanoscale environment. In this study, we demonstrate the conformational transition of a single pyrrolidine molecule adsorbed on a Cu(100) surface, driven by vibrational excitation through tunneling electrons using scanning tunneling microscopy. We identify multiple transition pathways between two structural states, each governed by distinct vibrational modes. The nuclear motions corresponding to these modes are elucidated through density functional theory calculations. By leveraging fundamental forces, including van der Waals interactions, dipole-dipole interactions, and steric hindrance, we precisely tune the molecule-environment coupling. This tuning enables the modulation of vibrational energies, adjustment of transition probabilities, and selection of the lowest-energy transition pathway. Our findings highlight how tunable force fields in a nanoscale cavity can govern molecular conformational transitions, providing a pathway to engineer molecule-environment interactions for targeted molecular functionalities.