Three-state molecular shuttles operated using acid/base stimuli with distinct outputs

Area of Science:

• Supramolecular Chemistry
• Materials Science
• Organic Chemistry

Background:

• Rotaxanes are mechanically interlocked molecules with potential applications in molecular machines.
• Controlling the translational motion of rotaxanes is key to their function.
• Acid-base stimuli offer a promising route for dynamic control of molecular architectures.

Purpose of the Study:

• To investigate the acid/base-mediated translational isomerization of novel [2]rotaxane systems.
• To explore the distinct binding interactions between crown ether and amine units under varying pH conditions.
• To correlate molecular states with observable spectroscopic outputs.

Main Methods:

• Synthesis of [2]rotaxanes featuring N-alkylaniline and N,N-dialkylamine binding sites.
• Acid-base titration to induce and study translational isomerization.
• UV-Vis spectroscopy to monitor changes in molecular states.

Main Results:

• Demonstrated three distinct translational states of the [2]rotaxanes controlled by pH.
• Identified specific binding preferences: dialkylamine-crown ether under neutral/acidic conditions, aniline-crown ether under basic conditions.
• Observed unique UV-Vis absorption signatures for each of the three states in a diphenylaniline-containing rotaxane.

Conclusions:

• Acid-base chemistry provides effective control over the translational states of [2]rotaxanes.
• The rotaxane system exhibits tunable recognition properties based on protonation.
• The observed spectroscopic changes enable optical detection of the molecular switching events.