A Dynamic Hydrogen-Bonded Azo-Macrocycle for Precisely Photo-Controlled Molecular Encapsulation and Release

Area of Science:

• Supramolecular Chemistry
• Photochemistry
• Materials Science

Background:

• Hydrogen-bonded azo-macrocycles offer potential for controlled molecular interactions.
• Photoisomerization of azo-compounds can induce structural changes in host molecules.
• Precise control over molecular encapsulation and release remains a challenge.

Purpose of the Study:

• To develop a light-responsive system for controlled molecular encapsulation and release.
• To investigate the effect of photoisomerization on macrocycle cavity size and guest exchange dynamics.
• To achieve quantitative and stepwise release of organic cations using light stimuli.

Main Methods:

• Density Functional Theory (DFT) calculations to model structural changes.
• Traveling Wave Ion Mobility Mass Spectrometry (TWIMS) to analyze molecular behavior.
• Nuclear Magnetic Resonance (NMR) spectroscopy to study host-guest exchange kinetics.

Main Results:

• Light-induced E→Z photoisomerization significantly decreased the macrocycle cavity size.
• The system demonstrated a rare 2:1 host-guest stoichiometry.
• Guest-dependent slow or fast exchange on the NMR timescale was observed.
• Quantitative capture and release of bipyridinium guests achieved, with a maximum release of 68%.

Conclusions:

• Slow host-guest exchange is crucial for accurate, stepwise release of organic cations under light irradiation.
• The developed light-responsive system enables precise control over molecular release processes.
• This work paves the way for advanced photoresponsive molecular switches and mechanically interlocked molecules.