Thermodynamic forecasting of mechanically interlocked switches

Area of Science:

• Supramolecular Chemistry
• Molecular Electronics
• Materials Science

Background:

• Mechanically interlocked molecular (MIM) switches, including [2]rotaxanes and [2]catenanes, are promising for molecular electronic devices (MEDs) and nanoelectromechanical systems (NEMS).
• Structural modifications and chemical environments significantly influence the thermodynamic behavior of molecular motions in MIMs, affecting device performance.
• Understanding these thermodynamic relationships is key to overcoming silicon chip density limitations.

Purpose of the Study:

• To establish a systematic and predictive thermodynamic approach for designing and tuning switchable MIMs and related materials.
• To link the noncovalent interactions in precursor pseudorotaxanes to the properties of the final MIM switches.
• To explore the potential of thermodynamic relationships in guiding the development of new molecular switches.

Main Methods:

• Isothermal titration microcalorimetry (ITC) was used to determine thermodynamic parameters of pseudorotaxane formation.
• A series of monosubstituted, acceptor host cyclophanes with various donor guests were synthesized and analyzed.
• X-ray crystallographic data were employed to complement ITC findings and understand structural details.

Main Results:

• A clear correlation was identified between noncovalent bonding interactions in pseudorotaxanes and the properties of the resulting MIMs.
• Changes in free energy during pseudorotaxane formation were successfully extrapolated to predict switching thermodynamics in analogous MIM switches.
• A predictive model was established for tuning the free energy differences (DeltaG(o)) in switchable MIMs.

Conclusions:

• The study demonstrates a reliable method for predicting and controlling the thermodynamics of MIM switches through precursor analysis.
• This thermodynamic approach facilitates the rational design of novel MIM-based molecular switches and materials.
• The findings offer a new perspective on structure-property relationships in supramolecular systems, reminiscent of classical concepts like parachor.