We report electroabsorption studies on poly(p-phenylene-vinylene) and polyazomethine over a large spectral range from 1.3 eV to 5 eV. Since these polymers are isoelectronic they provided an excellent test bed for an investigation into the interconnection between chemical and electronic structure. A proposal for the electronic energy levels including even-parity states is presented. The electroabsorption studies reveal that the introduction of nitrogen into the polymer chain considerably reduces the optical non-linearity. © 1998 Elsevier Science B.V.