A novel cationic fluorene-containing water-soluble poly(p-phenyleneethynylene) (PPE) derivative, poly [(9,9-bis{6'+N,N-diethyl)-N-methylammonium]hexyl)-2,7-fluorenyleneethyny lene)-alt-co-(2,5-bis(3'-[(N,N-diethyl)-N-methylammonium]-1'-oxapropyl}-1,4-phenylene)] tetraiodide (P1'), was synthesized through Sonogashira reaction and a post-polymerization treatment. P1' emits bright blue fluorescence in H2O with a high photoluminescence quantum yield (Phi(pl) = 26%). Studies on the optical properties and quenching experiments with Fe(CN)(6)(4-) in H2O and MeOH show that P1' presents minor aggregation and high Stern-Volmer constant (K-sv = 2.4 X 10(8) M-1) in aqueous solution. The remarkably reduced tendency towards aggregation, relative to previously reported water-soluble PPEs, made the optical properties of P1' almost insensitive to the disturbance from the common ions (non-quencher) in the solution. (c) 2006 Elsevier Ltd. All rights reserved.