Mechanochromic Copolymers with a Rhodamine-Rich Block

A new class of multirhodamine-based macromechanophores ( Rh-PETs ) are synthesized. Chain extension of Rh-PETs leads to a series of high mechanophore content copolymers including Rh-PET containing poly(methyl acrylate)s ( Rh-PET-PMAs ) and polyurethanes ( Rh-PET-PUs ). This platform allows for systematic analyses of mechanochromic properties of the polymers under sonication in the solution state and tension/compression in the bulk state in terms of their rhodamine content and molecular weight. Compared to their monorhodamine analogues, Rh-PET-PMAs and Rh-PET-PUs exhibit more efficient mechanochemical ring opening of rhodamine, reduced force threshold, and improved bulk mechanical properties. This design is thus revealed as a versatile methodology to promote the mechanochromic sensitivity of Rh-based stress-reporting polymers.