Thermally Stable Radical-Type Mechanochromic Polymers Based on Difluorenylsuccinonitrile.

Mechanochromism, a color change induced by mechanical force, has attracted much attention in materials science, as it can be used to create stress- and damage-detecting sensors. In particular, radical-type mechanochromic molecules (mechanochromophores), which produce colored radicals upon exposure to mechanical force, enable the qualitative visualization of mechanical stress and the quantitative evaluation of the generated radical species by electron paramagnetic resonance spectroscopy. However, the sensitivity of radical-type mechanochromophores to thermal stimuli limits their range of applications. Herein, we report the radical-type mechanochromophore difluorenylsuccinonitrile (DFSN), which can be used to synthesize mechanochromic polymers via living radical polymerization techniques, as its central carbon-carbon bond exhibits high thermal stability. The obtained DFSN-centered polymers show mechanochromism and desirably high thermal resistance.

Tetraarylsuccinonitriles as mechanochromophores to generate highly stable luminescent carbon-centered radicals.

This communication reports on the design and synthesis of mechanochromophores with a dynamic covalent system composed of a tetraarylsuccinonitrile skeleton that generate a metastable organic luminescent carbon radical. The mechanically generated radical species showed pink color and yellow light emission under UV irradiation. Unusually high stability of the luminescent carbon-centered radicals was also observed in a polymer system.