Tunable Fluorescence from a Responsive Hyperbranched Polymer with Spatially Arranged Fluorophore Arrays.

In the present study, a water-soluble hyperbranched polymer platform that contained a Förster resonance energy transfer (FRET) array and exhibited varied fluorescence in response to solvent, light, and CN- anion stimuli was constructed. The use of chain-growth copper-catalyzed azide-alkyne cycloaddition polymerization (CuAACP) enabled accurate control of the ratio and distance of three incorporated fluorophores, coumarin (Cou), nitrobenzoxadiazole (NBD), and photoswitchable spiropyran (SP), that could be reversibly transformed into the red-emitting merocyanine (MC) state. Within the FRET system, the energy flow from Cou to MC was significantly enhanced by the introduction of NBD as a central fluorophore relay. Moreover, the energy-transfer efficiency was increased by changing the solvent from tetrahydrofuran to more polar water; this was accompanied by a clear color change and fluorescence behavior. These correlations of polymer composition and solvent polarity to the FRET efficiency were finally applied to the effective detection of CN- anion; thus demonstrating a function of this polymer as a CN- sensor.