Poly [(m-phenylene vinylene)-alt-(o-phenylene vinylene)]s with different contents of cis-/trans-CH=CH (3 and 6) have been synthesized through Wittig condensation. The polymers exhibit good solubility in common organic solvents such as toluene and tetrahydrofuran. A comparison of the optical properties has been made between 3 and its phenyl regioisomers containing either p-phenylene or m-phenylene units. The results show that the regiochemistry of the phenyl ring can be a useful tool for tuning the emission color of pi-conjugated polymers because the extension of 7 conjugation can only partially be achieved through an o-phenylene bridge. Although both polymers 3 and 6 exhibit comparable low fluorescence quantum efficiencies (approximate to0.18) in solution, their films are highly luminescent, showing a broad emission band near 456 nm (blue color). Electroluminescence results show that the device of polymer 3, which has a higher content of trans-CH=CH linkages, is about 20 times more efficient than that of 6. (C) 2003 Wiley Periodicals, Inc.