Multiple Stimuli-Responsive Color-Changing Polymer Materials for Reversible Writing and Anti-Counterfeiting

Area of Science:

• Materials Science
• Polymer Chemistry

Background:

• Stimuli-responsive polymers offer diverse applications.
• Spiropyran (SP1) and spirothiopyran (STP) are key photochromic molecules.

Purpose of the Study:

• To develop novel polyurethane materials with multiple stimuli-responsive color changes.
• To explore the use of white light activation for spirothiopyran.

Main Methods:

• Covalent incorporation of spiropyran (SP1) and spirothiopyran (STP) into a polyurethane backbone.
• Investigating color changes induced by UV light, white light, mechanical stress, and heat.

Main Results:

• Successfully synthesized polyurethane polymers exhibiting photochromic, mechanochromic, and thermochromic properties.
• Discovered that white light (violet, blue, green) above a specific intensity activates STP to a green color.
• Achieved reversible three-color changes (brown, green, purple) in response to four distinct stimuli.
• Demonstrated high color contrast and excellent reversibility in the developed polymer materials.

Conclusions:

• The developed polyurethane materials exhibit unprecedented multi-stimuli responsive color-changing capabilities.
• The novel white light activation of STP expands the possibilities for stimuli-responsive materials.
• These materials show significant potential for applications in reversible writing, anticounterfeiting, and information encryption.