Multi-responsive fluorescence of amphiphilic diblock copolymer containing carboxylate azobenzene and N-isopropylacrylamide

One amphiphilic diblock copolymer poly(NIPAm-b-M6AzCOONa) with well-defined structure was synthesized by RAFT polymerization, in which N-isopropylacrylamide (NIPAM) was introduced as one thermoresponsive unit, and 6-[4-(4-sodium carboxylatephenylazo)phenoxyl]hexyl methacrylate (M6AzCOONa) was designed as pH-, UV-responsive and fluorescent units. The block copolymer was non-fluorescent in good solvent, but showed fluorescence emission when it formed micelle-like structures in water. The acquired fluorescence can be adjusted by UV or pH, which was strongly related to the aggregation tightness and size of the micelles. The block copolymer also showed reversible fluorescent enhancement in a large range of pH value (pH = 3-11) driven by thermally-induced coil-to-globule transition due to the existence of the PNIPAm block, which leads to a more closely-tightened aggregation of azobenzene moieties. These multiple-responsive fluorescence behaviors enable the amphiphilic block copolymer to find its applications for wide-pH-range fluorescence thermometer and fluorescence probe. (C) 2016 Elsevier Ltd. All rights reserved.