A series of silicon-containing phenylene-ethynylene polymers containing alkoxy groups (n-C6H13O- or n-C12H25O-), on some of the aromatic rings, has been synthesized by polycondensation using a palladium-catalyzed coupling reaction. The longer side chains led to greater solubility and higher crystallinity, as shown by wide-angle X-ray diffraction. The supramolecular structures of the polymers changed from ordered or semiordered to disordered structures as the Si component increased. A systematic blue shift was observed in the solution UV, solid-state UV, and solid-state emission spectra of the polymers with increasing silicon content. For all of the polymers except those with high silicon content, the emission spectra in dilute solution were quite similar, consistent with emission from localized excited states.