Hinge‐Like Mechanochromic Mechanophore Featuring 2,7‐Bis(phenylethynyl)pyrene

Pyrene derivatives substituted at the 2,7‐positions are rarely used in stimuli‐responsive materials, mainly because the nodal plane that passes through the 2,7‐positions in both the HOMO and LUMO makes their synthesis challenging. However, their photophysical properties, distinct from those of 1,6‐disubstituted pyrene derivatives, are promising for the development of stimuli‐responsive luminescent materials, because simply changing the substitution position, even with the same substituents, can significantly affect the fluorescence color change induced by external stimuli. In this study, we report a hinge‐like mechanophore featuring two 2,7‐bis(phenylethynyl)pyrene units. The rigidity of a [2.2]paracyclophane core, in which each benzene ring is shared with an individual luminophore, brings the luminophores into close proximity, resulting in excimer formation, though the monomer analogue shows no excimer emission even at high concentrations in THF. When covalently incorporated into a polyurethane elastomer, the mechanophore enables the film to exhibit an instantaneous and reversible fluorescence color change from excimer‐dominant sky‐blue to monomer‐dominant blue upon deformation. Notably, the fluorescence color change occurs at significantly shorter wavelengths than that observed for a previously reported hinge‐like mechanophore bearing two 1,6‐bis(phenylethynyl)pyrene units.