High solubility and photoluminescence quantum yield water-soluble polyfluorenes with dendronized amino acid side chains: synthesis, photophysical, and metal ion sensing properties

Abstract

A series of anionic water-soluble dendronized conjugated polymers PG0, PG1 and PG2 are synthesized by copolymerization of dendritic macromonomers and phenyldiboronic ester via direct Suzuki polycondensation reaction in THF–water solution. Water solubility and solution photoluminescence quantum yield increase with increasing the generation of the dendrons. PG2 exhibits an extremely high solubility which achieves 200 mg mL⁻¹ in aqueous solution and the corresponding quantum yield was measured to be 95%. The absorption and fluorescence spectra of the dendronized polymers are pH-dependent due to the aggregation of the polymer chains. PL spectrum of PG2 also exhibits better stability among large window of pH and high salt concentration than the other two polymers. Three polymers demonstrate different sensory behavior to metal ions. Among them, most metal ions can moderately quench the fluorescence of PG0, on the other hand, PG1 and PG2 have good selectivity and sensitivity to Hg²⁺ and Cu²⁺, respectively. Thin-films based on PG0, PG1, and PG2 are fabricated by spin-coating, layer-by-layer (LbL) deposition, and self-assembly on amine-functionalized quartz followed by thermal-annealing. Among them, the annealed films have good spectral stability in aqueous solution, which makes them promising materials for the application in the field of chemo- and biosensors and light-emitting devices.