Oxindolyl-Based Radicals with Tunable Mechanochromic and Thermochromic Behavior

Area of Science:

• Organic chemistry
• Materials science
• Supramolecular chemistry

Background:

• Dynamic covalent chemistry (DCC) utilizes reversible bond formation for stimuli-responsive materials.
• Organic radicals are promising for DCC but under-explored as building blocks.
• Stimuli-responsive chromic materials change color in response to external triggers.

Purpose of the Study:

• To synthesize and characterize novel oxindolyl-based mono-radicals (OxRs) for stimuli-responsive chromic materials.
• To investigate the dynamic covalent behavior of these OxRs, specifically their dimerization and dissociation.
• To explore how substituents influence the stability and responsiveness of the OxRs.

Main Methods:

• Synthesis of a series of oxindolyl-based mono-radicals with varying substituents.
• Structural confirmation of dimers using low-temperature 1H NMR and single-crystal X-ray diffraction.
• Investigation of stimuli-induced (temperature, pressure, solvent polarity) interconversion between monomers and dimers, coupled with color change observations.

Main Results:

• Successful synthesis and characterization of novel oxindolyl-based mono-radicals (OxRs).
• OxRs spontaneously dimerize, forming stable dimers whose structures were confirmed.
• Reversible monomer-dimer interconversion was achieved via stimuli, leading to distinct color changes.
• Substituent modification allowed tuning of mono-radical stability and bond dissociation energy.

Conclusions:

• Oxindolyl-based mono-radicals are effective building blocks for stimuli-responsive chromic materials.
• The dynamic covalent behavior of OxRs can be controlled by external stimuli and substituent effects.
• These novel OxRs show significant potential for developing advanced mechanochromic and thermochromic materials.