Fracture-induced mechanochemical activation is achieved for the first time in a structural engineering polymer. Rubber toughened PMMA is lightly cross-linked (1.0 mol%) with the mechanophore spiropyran by free radical polymerization. Single Edge Notch Tension tests are performed on the spiropyran-linked material and a distinct change in color and fluorescence is detected at the crack tip, indicating the mechanochemical transformation of the spiropyran molecules. The degree of mechanophore activation is quantified via fluorescence imaging and is observed to increase with increasing crack length. The region of mechanophore activation correlates directly with the size of the plastic zone ahead of the crack tip. (C) 2014 Elsevier Ltd. All rights reserved.