Molecular engineering has allowed the control of the HOMO-LUMO gap energy in a family of conjugated polymers based on poly(p-phenylenevinylene) (PPV). Random copolymerization of 1 and 6 afforded precursor polymers 10 with two different leaving groups. Treatment under thermal conditions led to a partially conjugated polymer 11 with regions of high and low HOMO-LUMO gap energy, showing a 30-fold improvement in electroluminescence efficiency compared with PPV, while treatment under acidic and thermal conditions gave more substantially conjugated polymers 12 with lower HOMO-LUMO gap energies. This chemistry enabled the formation of lithographically patterned polymers exhibiting electroluminescence. The scope of these copolymerizations was also explored with other copolymers, 19 and 22b,c.