Emergent complexity of quantum rotation tunneling.

Conformational isomerism determines the performance of materials and the activity of biomolecules. However, a complete dynamic study of conformational isomerization is still a formidable challenge at the single-molecule level. In this work, we present real-time in situ electrical monitoring of the full rotation dynamics of a single aromatic chain covalently embedded in graphene electrodes with single-event resolution. We reveal that the dynamic process of phenyl ring rotations at low temperature is dominated by quantum rotation tunneling rather than the quasi-free rotation process. The emergent complexity of different intramolecular rotations in a single aromatic molecule is demonstrated, including the alternating unidirectional rotation with multi-, single-, and half-circle delays driven by inelastic electron tunneling, which has not been previously adequately considered at the macroscopic level. This work builds a bridge between macroscopic and microscopic worlds and improves our understanding of structure-activity relationships, potentially bringing different functions to ordinary materials.