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Area of Science:

  • Supramolecular Chemistry
  • Nanotechnology
  • Materials Science

Background:

  • Artificial molecular machines offer potential beyond biological systems.
  • Understanding noncovalent interactions is key to designing molecular devices.
  • Metal-organic coordination networks provide frameworks for molecular assembly.

Purpose of the Study:

  • To investigate the complex behavior of supramolecular rotors within a 2D metal-organic coordination network.
  • To elucidate the role of noncovalent interactions and transient rearrangements in rotor dynamics.
  • To define and explore mechanical cooperativity in artificial molecular machines.

Main Methods:

  • Combined scanning tunneling microscopy (STM) experiments and molecular dynamics (MD) modeling.
  • Precise measurement of rotation rates (0.2 kcal mol(-1) / 9 meV precision).
  • Analysis of collective rotation events and reconfigurations in chiral trimeric units.

Main Results:

  • Stereoisomerization of chiral units leads to topological isomerization.
  • Molecular rotor rotation occurs via a two-step, asynchronous, topology-conserving process.
  • Distinct subunit displacements lower rotation barriers compared to rigid rotors, demonstrating mechanical cooperativity.

Conclusions:

  • Supramolecular rotors exhibit unique dynamic behaviors governed by noncovalent interactions.
  • The chemical environment can be used to control the dynamics of these molecular machines.
  • Mechanical cooperativity significantly reduces free energy barriers in supramolecules compared to rigid counterparts.