Optical properties were compared between the isomeric poly[(2,5-dialkoxy-1,4-phenylenevinylene)-alt-(1,3-phenylenevinylene)] derivatives with different content of cis-/trans-vinylene bond linkages. The polymer of about 33% vinylene in the trans-configuration exhibited an absorption lambda(max) approximate to 394 nm, which was blue-shifted by as much as 20 nm from its trans-vinylene-enriched isomer (lambda(max) approximate to 413 nm). The content of trans-vinylene, however, showed smaller impact on the photoluminescence (about 4 nm difference observed in their fluorescence lambda(max)). The vibronic structure in the emission spectra was determined with the aid of low temperature spectra. An light-emitting diode (LED) device using cis-vinylene-enriched sample gave green emission (lambda(max) approximate to 500 nm). The maximum external quantum efficiency of the device was determined to be 0.27%. (c) 2005 Elsevier B.V. All rights reserved.