A Visible Light Responsive On-Off Polymeric Photoswitch for the Colorimetric Detection of Nerve Agent Mimics in Solution and in the Vapor Phase

A polymeric probe derived from a visible light responsive donor acceptor Stenhouse adduct (DASA) was designed for the rapid and selective colorimetric detection of nerve agent mimics. Glycidyl methacrylate (GMA) and dimethylacrylamide (DMA) were copolymerized by reversible addition fragmentation chain transfer (RAFT) polymerization to yield poly(glycidyl methacrylate-co-dimethylacrylamide) [p(GMA-co-DMA)], herein P1. The epoxide unit of P1 was transformed to 1-((2-(2-hydroxyethoxy)ethyl)amino)-3-methoxypropan-2-ol by the reaction with 2-(2-aminoethoxy)ethanol, leading to P2. The subsequent reaction between the secondary amine of P2 with 5-(furan-2-ylmethylene)-1,3-dimethylpyrimidine-2,4,6(1H,3H,SH)-trione yielded P3 with DASA derivatives. P3 exhibited the rapid and selective detection of diethyl cyanophosphate (DCNP), a mimic of the nerve agent, in both solution and the vapor phase. Upon the exposure to DCNP, the color of the P3 solution/film turned from purple to colorless due to the formation of morpholino cations, induced by DCNP-promoted intramolecular N-alkylation. The availability of the electron-rich N-alkyl unit in the triene unit of the DASA chromophore allowed P3 to show excellent sensing behavior toward DCNP. DASA-incorporated P3 has also shown excellent photochromic performance upon irradiation with visible light. Zwitterionic cyclopentenone units formed by irradiation with visible light prevented the DCNP-promoted intramolecular N-alkylation, resulting in no colorimetric responses toward DCNP. Thus, these photocontrollable properties of P3 can offer new insights into the design of new photoresponsive on off polymeric switches, for colorimetric on off detection of nerve agent mimics.