pi-Conjugated cooligomers consisted of 2,6-dialkoxynaphthalene-1,5-diyl (RNap), 2,1,3-benzothiadiazole-4,7-diyl, and 1,4-phenylenediethynylene units were synthesized by Pd-complex-catalyzed condensation reactions. The UV-Vis, photoluminescence, and powder X-ray diffraction measurements suggested that the oligomers have self-assembling-ordered structures in the solid state. The ordered structures depended on the distance between the RNap units of the oligomers. The oligomers underwent electrochemical oxidation (p-doping), which occurred at lower potentials for films than for acetonitrile solutions containing [Et4N]BF4. This effect is caused by the longer pi-conjugation lengths of the oligomers in films, which was attributed to molecular self-assembly leading to ordered structures in the solid state.