Mechanically Activated Luminescence in Polyurethanes Incorporating Calixarene Mechanophores

Area of Science:

• Supramolecular Chemistry
• Materials Science
• Organic Chemistry

Background:

• Calixarenes are macrocyclic compounds with tunable conformational properties.
• Mechanoluminophores are materials that emit light in response to mechanical stimuli.
• Developing new mechanoluminophores is crucial for advanced sensor applications.

Purpose of the Study:

• To develop the first calixarene-based mechanoluminophore.
• To investigate the relationship between mechanical force and luminescence changes.
• To establish a general design strategy for supramolecular mechanophores.

Main Methods:

• Functionalization of cone calix[4]arenes with pyrene moieties.
• Formation of intramolecular ground-state excimers.
• Incorporation into linear polyurethanes to form films.
• Mechanical testing using manual stretching and a universal tensile tester.
• Spectroscopic analysis (¹H NMR, fluorescence spectroscopy).

Main Results:

• A novel calixarene-based mechanoluminophore was successfully synthesized.
• Stretching polyurethane films containing the mechanoluminophore induced a reversible fluorescence shift from green-yellow to blue.
• The observed fluorescence change is attributed to force-induced conformational changes in the calixarene scaffold, leading to excimer-to-monomer transitions.
• The material demonstrated reversible and repeatable responses over multiple stress/release cycles.

Conclusions:

• The conformational flexibility of calixarenes can be exploited to create effective mechanoluminophores.
• This design prevents intermolecular aggregation effects, leading to reliable performance.
• The developed calixarene mechanoluminophore offers a promising platform for developing advanced stress-responsive materials and sensors.