Abstract
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) (CBPQT4+, 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 CBPQT4+, 4Cl− in aqueous media was studied by means of UV–Vis, NMR (1H, 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.
Highlights
Stimuli-responsive polymeric materials have attracted considerable attention and have become a much studied sub-discipline in contemporary polymer chemistry [1,2,3,4,5,6]
A novel Reversible Addition-Fragmentation Chain Transfer (RAFT) agent Napht-N-CTA was conveniently prepared from the coupling reaction of 1,5-bis [2-(2-hydroxyethoxy)ethylamino]naphthalene [34] 1 and 2-(1isobutyl)sulfanylthiocarbonylsulfanyl-2-methyl propionic acid
The ability of the Napht-N-CTA to promote RAFT polymerizations was demonstrated with N-isopropylacrylamide (NIPAM)
Summary
Stimuli-responsive polymeric materials have attracted considerable attention and have become a much studied sub-discipline in contemporary polymer chemistry [1,2,3,4,5,6]. The last decade has provided stimuli-responsive polymers capable of sensing and responding to environmental changes or the presence of analytes Compared to their molecular-scale brethren, macromolecular based sensors offer several advantages including improved detection sensitivity, better dispersibility in aqueous media, and flexibility of processing facilitating their integration into viable devices. Temperature and pH play a central role in many fields of science and engineering, and as a consequence, attention has been directed towards the design of smart polymeric systems capable of monitoring these two parameters Our group has reported a straightforward supramolecular approach to elaborate a new family of thermosensors with an associated direct visible readout [33] This host-guest concept is based on the thermoresponsiveness of coloured complexes formed from naphthalene functionalized PNIPAM as guests and cyclobis(paraquat-p-phenylene) (CBPQT4+, 4ClÀ) as host. The synthesis of Napht-N-PNIPAM and its propensity to form a strong coloured host–guest assembly in aqueous media with CBPQT4+, 4ClÀ is reported in detail, as well as the thermo and pH responsiveness of Napht-N-PNIPAMÁCBPQT supramolecular complex
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