A Rhodamine-Spiropyran Conjugate Empowering Tunable Mechanochromism in Polymers under Multiple Stimuli

Area of Science:

• Materials Science
• Polymer Chemistry
• Optoelectronics

Background:

• Mechanochromic polymers utilize force-responsive mechanophores for damage sensing and data storage.
• Existing mechanophores often have limited sensitivity or require complex fabrication for multi-modal color changes.
• There is a need for mechanophores with tunable chromic characteristics and multi-stimuli responsiveness.

Purpose of the Study:

• To develop a novel multifunctional mechanophore with tunable mechanochromism in polymers.
• To investigate the synergistic optical coupling of fused rhodamine and spiropyran (Rh-SP) subunits.
• To engineer elastomers with programmable, wide-spectrum colors and enhanced sensing capabilities.

Main Methods:

• Synthesized Rh-SP-linked polymers with polymer chains tethered to both rhodamine and spiropyran subunits.
• Evaluated mechanochromic behaviors under sonication and compression, analyzing force response and light-controlled relaxation.
• Investigated non-sequential ring-opening and differential ring-closing reactions of the subunits.

Main Results:

• Achieved vividly detectable and tunable mechanochromism in polymers via the novel Rh-SP mechanophore.
• Demonstrated high-contrast mechanochromism due to non-sequential ring-opening of the two subunits under force.
• Engineered programmable, wide-spectrum colors in elastomers using light-induced differential ring-closing and acidichromism.

Conclusions:

• Presents an effective strategy for highly appreciable and regulable mechanochromic functionality in polymers.
• Provides new insights into the rupture mechanisms of π-fused mechanophores.
• Elucidates how stimuli history influences stress accumulation and mechanochromic response in polymers.