Hinge‐Like Mechanochromic Mechanophores Based on [2.2]Paracyclophane

Abstract

Abstract A hinge‐like supramolecular mechanophore based on a [2.2]paracyclophane core and two excimer‐forming 1,6‐bis(phenylethynyl)pyrene luminophores is presented. Each luminophore shares one phenyl group with the [2.2]paracyclophane, resulting in a rigid and strained structure that forces the two luminophores into close proximity. As a consequence, the photoluminescence of the mechanophore in THF solution and in solid films of a polyurethane containing the new motif is dominated by excimer emission. Stretching the polymer films causes an easily discernible change from bright yellow excimer to blue–green monomer‐dominated emission. The ratio of excimer to monomer emission intensities traces the nonlinear stress–strain curves of the polymer well and is a good indicator for the macroscopically applied force. The reversibility of the mechanoresponse, theoretical analyses, and reference experiments with a similar mechanophore in which the emitters and the [2.2]paracyclophane core are connected by flexible linkers support the conclusion that the mechanoactivation is caused by distorting the molecule into a bent, more open conformation and not the scission of covalent bonds. The operating principle was further confirmed by investigating a second hinge‐like mechanophore based on a [2.2]paracyclophane core and 1,4‐bis(phenylethynyl)benzene emitters.