Multicolor mechanochromism of a multinetwork elastomer that can distinguish between low and high stress

Mechanochromic polymers (MCPs), which respond to mechanical stimuli via an optical signal change, are regarded for their application in smart materials, such as force sensors. Although rapid progress in MCPs has been witnessed in recent years, MCPs systems that can distinguish different magnitudes of stretching or compression stress through multicolor transformation are still hard to achieve. In this paper, we report our findings on a multicolor mechanochromic elastomer that can discriminate between low and high stretching stress. The key point of our design depends on the introduction of two mechanophores, which present different fluorescence changes in response to mechanical stimuli. These mechanophores were elaborately introduced to the multi-network elastomer though a multiple swelling–UV polymerization process. Under relatively low tensile stress (≲1.8 MPa), the formation of a blue-fluorescence anthracene derivative was observed, while under high tensile stress (≳1.8 MPa), both mechanophores were activated. Thus, the elastomer exhibited a blue-white and further red fluorescence. Although the present results remain preliminary, the macroscopic fluorescence change at different levels of stress could indicate where the stress is concentrated, which would be beneficial to elucidate the mechanism of material failures.