A water-soluble supramolecular polymeric dual sensor for temperature and pH with an associated direct visible readout

We report a multi-stimuli responsive polymeric sensor consisting of a pseudorotaxane-like architecture fabricated from a 1,5-diaminonaphthalene end-functionalized poly(N-isopropyl)acrylamide (Napht-N-PNIPAM) and cyclobis(paraquat-p-phenylene) (CBPQT(4+), 4Cl(-)). The coloured nature of the poly-pseudorotaxane provides a sensor for temperature and pH in water with an associated visible readout. To create this dual responsive polymeric sensor, a new chain transfer agent (Napht-N-CTA) incorporating a pH-responsive 1,5-diaminonaphthalene unit was synthesized and used for the polymerization of N-isopropylacrylamide via Reversible Addition-Fragmentation Chain Transfer (RAFT). The ability of Napht-N-PNIPAM to form a pseudorotaxane architecture with CBPQT(4+), 4Cl(-) in aqueous media was studied by means of UV-Vis, NMR (H-1, 2D-ROESY, DOSY) and ITC experiments. Interestingly, the pseudorotaxane architecture can be reversibly dissociated upon either heating the sample above its cloud point or protonating the nitrogen atoms of the 1,5-diaminonaphthalene-based guest unit by adjusting the pH to around 1. In both cases a dramatic colour change occurs from intense blue-green to colourless. (C) 2015 The Authors. Published by Elsevier Ltd.