Synthesis, characterization and self-assembly behavior in water as fluorescent sensors of cationic water-soluble conjugated polyfluorene-b-poly(N-isopropylacrylamide) diblock copolymers

A series of well-defined novel water-soluble diblock copolymers containing conjugated amino-terminal polyfluorene (PF) block and coil-like poly(N-isopropylacrylamide) (PNIPAM) have been successfully synthesized through atom transfer radical polymerization (ATRP) initiated by a 2-bromoisobutyrate end-capped PF macroinitiator using CuCl/HMTETA (1,1,4,7,10,10-hexamethyltriethylenetetramine) as the catalyst. The first-order kinetic plots indicate the presence of a constant number of active species during the polymerization. The molecular weight and molecular weight distribution can be well controlled, implying synthesis of well-defined block structures of the copolymers. The chemical structures of block copolymers have been characterized by 1H NMR, UV-vis, and photoluminescence (PL) spectra. PF aggregates are formed in water with the increase of temperature for the conjugated-ionic diblock copolymer synthesized, as confirmed by dynamic light scattering (DLS). The formation of excimers within the PF aggregates results in improved Förster resonance energy transfer (FRET) efficiencies.