Poly [(2-alkyloxy-5-methyl- 1,3-phenylenevinylene)-alt-(1,3-phenylenevinylene)]s (8) and poly[(2-alkyloxy-5-methyl-1,3-phenylenevinylene)-alt-(1,4-phenylenevinylene)]s (10) were synthesized by the Wittig reaction to provide materials containing 45-62% cis-vinylene bonds. The optical characteristics of 8 and 10 were compared with those of their respective isomers, 3 and 4, the cis-vinylene contents of which were significantly lower (9-16%). Although a greater fraction of cis-CH=CH linkages caused the absorption maximum (lambda(max)) of 8 and 10 to be slightly blueshifted (by similar to3-6 nm) from that of 3 and 4, the impact of the vinylene bond geometry appeared to be negligible on their fluorescence spectra. The fluorescence quantum efficiencies of 8 and 10 were estimated to be approximately 0.25 and 0.72, respectively. Both 8 (lambda(max) - 445 or 462 nm) and 10 (lambda(max) approximate to 480 or 506 nm) were electroluminescent, showing effective color tuning by the controlled insertion of m-phenylene moieties. The external electroluminescence quantum efficiencies were determined to be 4.26 X 10(-3)% for 8 and 0.63% for 10. The cis/trans-vinylene bond ratio had a great impact on the electroluminescence device performance of 8 but a much smaller impact on the performance of 10. (C) 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 303-316, 2004