A detailed and systematic investigation of mechanochromic, melt-processed blends between a series of polyethylenes (PE) with crystallinities ranging from 9 to 66% and two excimer-forming, photoluminescent oligo(phenylenevinylene) dyes is described. A dramatic increase in the nucleation rate of dye aggregates, and therewith a decrease in the size of the aggregates, is observed upon grafting long alkyl tails onto the chromophore. The extent of color change observed upon deformation of these materials, and thus the ability of the polymer host to break up dye aggregates upon deformation, is related to the plastic deformation process of PE crystallites-specifically those arranged in a lamellar morphologyand increases with increasing polymer crystallinity, decreasing dye aggregate size, and decreasing rates of deformation.