Fluorescence properties of a series of cationic poly(p-phenylenevinylene) (PPV) derivatives with different contents of cis- and trans-vinylic linkages quenched by Fe(CN)(6)(4-) were intensively investigated. PPVs with cis-/trans-vinylic linkages display downward Stern-Volmer curves indicating incomplete quenching. The fluorescence quenching mechanism and the effect of many factors possible on the incomplete quenching has been examined, and the difference of the quenching behavior of two isomers was investigated, which further confirmed that the presence of cis-vinylic linkages would most probably cause inaccessible fluorophores and thus the incomplete quenching. (C) 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 336-341, 2010