A Photoswitchable Macrocycle Controls Anion-Templated Pseudorotaxane Formation and Axle Relocalization.

Area of Science:

• Supramolecular Chemistry
• Organic Chemistry
• Materials Science

Background:

• Biological processes like signaling and transport rely on controlled molecular binding events.
• Artificial supramolecular systems offer a platform to mimic these dynamic biological functions.

Purpose of the Study:

• To design and synthesize light-responsive macrocyclic compounds.
• To investigate their ability to form and release pseudorotaxane complexes upon photoisomerization.

Main Methods:

• Synthesis of stiff-stilbene-containing macrocycles.
• Photoisomerization studies using UV/Vis and proton nuclear magnetic resonance (¹H NMR) spectroscopy.
• Complexation studies with pyridinium halide axles using ¹H NMR titration and single-crystal X-ray crystallography.
• Computational simulations to model molecular interactions.

Main Results:

• Stiff-stilbene macrocycles were synthesized and isomerized between (Z) and (E) forms using light.
• (Z)-isomers effectively formed stable pseudorotaxane complexes with pyridinium halide axles.
• Complex stability was tunable via the counteranion.
• Light-induced isomerization to the (E)-isomer significantly reduced axle binding.
• Axle exchange between the macrocycle and a secondary isophthalamide host was triggered by light.

Conclusions:

• Light-switchable macrocycles can control the formation and disassembly of supramolecular complexes.
• This system demonstrates a mechanism for light-triggered molecular recognition and release.
• The findings pave the way for developing advanced artificial systems for molecular signaling and transport.