Water-Soluble Polymeric Probes for the Selective Sensing of Mercury Ion: pH-Driven Controllable Detection Sensitivity and Time

Polymeric probes with dithioacetal units in the side chains were designed and synthesized for the selective and efficient colorimetric sensing of Hg²⁺ ions in aqueous solutions. These polymeric sensors were prepared by a reaction between aldehyde groups of the side chain in the polymer and ethanethiol or 3-mercaptopropionic acid using BF₃ as a Lewis acid. In aqueous solution, they exhibited a 30–40 nm red-shift in their absorption maxima upon the addition of Hg²⁺ ions, accompanied by a change in the color of the solution, from pale yellow to dark red. These results clearly demonstrated that the sensitive signaling behaviors originated from the Hg²⁺-promoted deprotection reaction of dithioacetal groups to form aldehyde functionalities. The sensors have excellent selectivity toward Hg²⁺ ions over other alkali and transition metal ions. The detection time for Hg²⁺ ion was finely tuned by a change in the pH of the solution. In particular, it took less than 1 min to complete Hg²⁺ ion detection at low pH. Given with fast and pH-tunable Hg²⁺ ion detection abilities, these polymeric probes are expected to offer unique potential platforms for integrating stimuli-responsive water-soluble polymers with tunable sensing behaviors

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-<i>co</i>-dimethyl­acrylamide) [p­(GMA-<i>co</i>-DMA)], herein <b>P1</b>. The epoxide unit of <b>P1</b> was transformed to 1-((2-(2-hydroxy­ethoxy)­ethyl)­amino)-3-methoxy­propan-2-ol by the reaction with 2-(2-amino­ethoxy)­ethanol, leading to <b>P2</b>. The subsequent reaction between the secondary amine of <b>P2</b> with 5-(furan-2-ylmethylene)-1,3-dimethyl­pyrimidine-2,4,6­(1<i>H</i>,3<i>H</i>,5<i>H</i>)-trione yielded <b>P3</b> with DASA derivatives. <b>P3</b> 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 <b>P3</b> 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 <b>P3</b> to show excellent sensing behavior toward DCNP. DASA-incorporated <b>P3</b> 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 <b>P3</b> can offer new insights into the design of new photoresponsive on–off polymeric switches, for colorimetric on–off detection of nerve agent mimics

Solid State Assemblies and Photophysical Characteristics of Linear and Bent-Core π‑Conjugated Oligophenylenevinylenes

New classes of luminescent linear, bent-core, and star-shaped oligophenylenevinylenes (OPVs) having 1,4-para and 1,3-meta rigid aromatic cores were designed and developed. 3-Pentadecylphenol, a renewable resource molecule, was chosen as the flexible unit at the longitudinal or middle position of the OPV aromatic core for solid state ordering. Depending upon the nature of the π-core, the OPVs exhibited either mosaic-type liquid crystalline textures or spherulitic crystalline solids. The enthalpies of melting transitions revealed that the bent-core OPV structure showed enhanced solid state packing compared to linear or star-shaped OPVs. Small and wide-angle X-ray diffraction analysis confirmed layered-like assemblies in OPV molecules. Photophysical experiments such as excitation, emission, and time-resolved fluorescence decay dynamics were carried out to trace the molecular self-organization of OPV chromophores. Time correlated single photon counting technique (TCSPC) luminescent decay profiles and decay lifetimes (τ₁ and τ₂ values) revealed that the OPV chromophores showed faster exciton decay in the tightly packed bent-core structure. The weakly packed star-shaped OPV showed enhanced excited state luminescence stability up to 10 ns. A direct correlation between the OPV chemical structure, solid state ordering, and photophysical characteristics was established

Substrate-Independent Approach to Dense Cleavable Polymer Brushes by Nitroxide-Mediated Polymerization

High grafting density polymer brushes are grown on an inimer coating bearing nitroxide-mediated polymerization (NMP) inimers and glycidyl methacrylate (GMA). The inimer coating is cross-linked on the substrate to provide an initiator layer with needed stability during long exposure to organic solvents at moderate to high temperatures. Surface-initiated nitroxide-mediated polymerization (SI-NMP) is conducted to grow polystyrene (PS) brushes on the coating with a sacrificial layer designed to cleave the brushes. The cleaved brushes have larger molecular weights than the corresponding free polymers. The grafting density of the brushes is as high as 1.12 chains/nm² throughout the brush growth, which is among the densest PS brushes reported so far. Atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) depth profiling are used to reveal the surface morphology and kinetics of the growth