A pair of cationic phenylene ethynylene oligomers (OPEs) have been synthesized, and their optical properties have been studied in solution with and without added scaffold materials, including carboxymethylcellulose, carboxym-ethylamylose, and Laponite. The OPEs are strongly fluorescent in methanol solution, but in water, the fluorescence yield is suppressed. The addition of scaffolds to aqueous solutions of OPEs leads to a red shift in the absorption and in most cases a significant increase in the fluorescence quantum yield. The effects most likely arise because of template-induced formation of linear J-dimers or possibly because of planarization, which give rise to an effective increase in the conjugation length of OPEs.