Neat films and solutions of poly[1,4-phenylene-1,2-di(4-phenoxyphenyl)vinylene], poly[1,4-phenylene-1,2-di(phenthiophenyl)vinylene], poly[4,4'-diphenylene-1,2-di(4-phenoxyphenyl)vinylene] and poly [4,4'-diphenylene-1,2-di(4-fluorophenyl)vinylene] in 1,4-dioxane are investigated. The optical constants of the neat films are determined, absorption and fluorescence data are analysed, and picosecond laser saturable absorption studies are carried out. The fluorescence lifetimes and fluorescence quantum yields are analysed to determine the emitting chromophore size (electronic delocalization). The saturable absorption measurements are used to determine the average absorption segment size. (C) 2001 Elsevier Science Ltd. All rights reserved.