A new stepwise synthesis method for the preparation of precisely defined oligo(p-phenyleneethynylene)s (OPEs) is described. High-purity monomer, trimer, pentamer, heptamer, and nonamer of OPEs with dihexyloxy side groups and trimethylsilyl (TMS) or thioacetyl (SAc) terminals have been synthesized. The structures of the oligomers were characterized by H-1 NMR, C-13 NMR, and elemental analysis. DSC studies show narrow and well-developed melting and crystallization peaks, indicating the high perfection of the crystals formed in these oligomers. Optical microscopy was used for investigating the supramolecular morphology of solid-state films of pentamer with TMS end groups, as an example. Numerous dendrites with a spherulitic size of ca. 50mum were observed. UV-vis absorption and photoluminescence (PL) spectra in both dilute solution and films show a gradual red shift of the lambda(max) from trimer to nonamer. At the nonamer stage, the optical maximum is approaching a limit of convergence.