A fluorene-containing water-soluble poly(p-phenyleneethynylene) derivative: Highly fluorescent and sensitive conjugated polymer with minor aggregation in aqueous solution

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-fluorenyleneethynylene)-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 (Φ_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=2.4×10⁸ 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.