Optical reporting of covalent bond scission in self-assembled structures in water is an important step toward the detection of forces in biological systems. Here we show that micelles of a diblock copolymer comprising hydrophobic poly(butyl acrylate) and hydrophilic poly(acrylic acid) blocks connected by an off-center mechanoresponsive moiety are mechanochemically active when sonicated in aqueous solution. Facile optical read-out of the force-activation is warranted by formation of a blue-fluorescent anthracene cleavage from the mechanophore, an anthracene-maleimide Diels-Alder adduct. In contrast to the efficient bond scission when the block copolymers are noncovalently anchored in liquid-like micellar cores, isolated unimers in solution are not activated by ultrasonication because the dimensions and viscous drag are drastically lower. These results demonstrate that covalent mechanochemistry can be enabled by noncovalent interactions.