A series of substituted poly(p-phenyleneethynylene)s, PPE, were synthesized by alkyne metathesis. The substituents dibutyl 4a, dioctyl 4b, ditetradecyl 4c, di-2-ethylhexyl 4d, and di-2cyclohexylethyl 4e were placed on the 2,5-positions of the phenyl rings. X-ray diffraction studies indicated that the main chains of each polymer were arranged in regular, layered arrays. Liquid crystalline structures were obtained by polarized optical microscopy in PPE 4b, 4c, and 4d. The temperatures of isotropization of the liquid crystalline structures coincided with the disordering temperatures determined by differential scanning calorimetry. The UV absorption spectra showed a gradual blue shift of the lambda (max) from 4a to 4e, suggesting a decrease in the electronic delocalization along the chain as the size and geometry of the side group changed. The photoluminescence spectra in dilute toluene solutions are consistent with vibronic coupling and emission from localized excited states. The emission spectra of thin films show characteristics typical excimer or aggregate formation in the solid state. Last, an improved method of molecular weight determination by end group analysis was devised.