A double-spiro ring-structured mechanophore with dual-signal mechanochromism and multistate mechanochemical behavior: non-sequential ring-opening and multimodal analysis

Herein, we report a novel aminobenzopyranoxanthene (ABPX) mechanophore featuring double spiro rings. ABPXs were introduced into a series of poly(methyl acrylate)s (PMAs) with different molecular weights to experience gradient forces exerted by ultrasonication in dilute solution. The fluorescence spectra and multimodal analysis of the absorption spectra confirm polymer mechanochromism with a dual-signal response and two mechanogenerated ring-opened isomers, of which the relative distribution is modulated by the external force based on the heat-force equilibrium. The empirical model and the mechanism of non-sequential ring-opening are established to describe and explain the force-dependent distribution of two mechanochemical products. CoGEF calculations also confirm the mechanochemical fragility of ABPXs.