Water‐soluble dendritic‐conjugated polyfluorenes: Synthesis,characterization, and interactions with DNA

Three generation of Boc‐protected dendritic‐conjugated polyfluorenes ( Boc‐PFP‐G_0‐2 ) were synthesized by Suzuki coupling 1,4‐phenyldiboronic ester with dendritic monomers that were synthesized through generation‐by‐generation approach. The gel permeation chromatography (GPC) analyses showed that the weight‐average molecular weight (M_w) of Boc‐PFP‐G_0‐2 was in the range of 11,400–20,400 Da with the polydispersity index (PDI) in the range of 1.32–1.96. Treatment of Boc‐protected polymers with 6 M HCl in dioxane yielded cationic dendritic‐conjugated polyfluorenes ( PFP‐G_0‐2 ). They were soluble in common polar solvents such as DMSO, DMF, and water with absorption maxima between 345 and 379 nm. The solutions of PFP‐G_0‐2 in water were highly fluorescent with emission maxima between 416 and 425 nm. Because higher generation dendrons could prevent the formation of π‐stacking aggregates of backbones of conjugated polymer, the fluorescence quantum efficiencies (QEs) of PFP‐G_0‐2 enhance as the dendritic generation grew. The interactions between 25 mer double‐stranded DNA (dsDNA) and PFP‐G_0‐2 were studied using ethidium bromide (EB) as fluorescent probe. The electrostatic bindings of PFP‐G_0‐2 with dsDNA/EB complex result in displacement of EB from DNA double helix to the solution accompanying by a quenching of EB fluorescence. The PFP‐G₂ with highest generation of dendritic side chains possessed a highest charge density and could form most stable complex with dsDNA. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 7462–7472, 2008