Block copolymers of dibenzofulvene and methyl methacrylate obtained by living anionic polymerization formed stable, soluble nanoparticles by in situ molecular aggregation of the poly(dibenzofulvene) segments having a rigid pi-stacked conformation; the nanoparticles indicated red-shifted absorption bands and reduced oxidation potential relative to a single chain poly (dibenzofulvene).