Poly(aryleneethynylene) Tongue That Identifies Nonsteroidal Anti-Inflammatory Drugs in Water: A Test Case for Combating Counterfeit Drugs

We report a sensor array composed of a highly fluorescent positively charged poly­(<i>para</i>-phenyleneethynylene) <b>P1</b> and its complex <b>C</b> with a negatively charged pyridine-containing poly­(<i>para</i>-aryleneethynylene) <b>P2</b> (quencher) at pH 10 and pH 13; a sensor field composed of four elements, <b>P1</b> (pH 10), <b>P1</b> (pH 13), <b>C</b> (pH 10), and <b>C</b> (pH 13), results. The elements of this small sensor field experience either fluorescence turn on or fluorescence quenching upon exposure toward nonsteroidal anti-inflammatory drugs (NSAIDs), such as aspirin, ibuprofen, diclofenac, or naproxen. The combined responses of the sensor field are analyzed by linear discriminant analysis (LDA). All of the NSAIDs were identified and discriminated, and the sensing mechanism, hydrophobic versus electrostatic, was discussed

Solid-State Gels of Poly(<i>p</i>‑phenyleneethynylene)s by Solvent Exchange

Solutions of dialkoxy- and dialkyl-poly­(<i>p</i>-phenyleneethynylene)­s (PPE) form well-defined solid state gels by diffusion of a nonsolvent (SOG), even if the concentration of the PPEs is only 2.5 mg/mL. The residual solvent in the SOG gel does not contain any dissolved PPE according to fluorescence and emissive lifetime measurements. The solvent inside of the gels is confirmed to be more than 90% of the polar solvent, which gives temperature stability to the gel and makes it available for infiltration of analytes, etc. This is in strong contrast to “classic” gels that form by thermal gelation; these still contain dissolved PPE chains. As a result, an ionic-liquid-filled PPE gel could be formed successfully by solvent exchange

From Linear to Foldamer and Assembly: Hierarchical Transformation of a Coplanar Conjugated Polymer into a Microsphere

Despite the coplanar structure, a conjugated alternating copolymer forms amorphous, well-defined microspheres without π-stacked crystalline domains. Here, we gain insights into the mechanism of how the coplanar conjugated polymer forms amorphous microspheres by means of spectroscopic studies on the assembly/disassembly processes. The difference of the spectral profiles of photoabsorption and photoluminescence with varying solvent/nonsolvent composition clarifies that stepwise assembly takes place through the microsphere formation; [1] intrapolymer linear-to-folding transformation upon diffusion of polar nonsolvent and [2] interpolymer assembly of the foldamers upon further addition of the nonsolvent to form microspheres. As shown in various biopolymers such as proteins and DNA, such stepwise folding and assembly behaviors of conjugated polymers from primary to secondary and tertiary structure open a new way to create transformable functional materials

Whispering Gallery Resonance from Self-Assembled Microspheres of Highly Fluorescent Isolated Conjugated Polymers

Self-assembly of highly fluorescent isolated conjugated polymers (ICPs), comprising alternating phenylene moieties with an insulating cyclic side chain and different arylene moieties, was comprehensively studied. Two out of nine ICPs were identified to form well-defined spheres of 1–6 μm diameter. The degree of twisting of the main chains was found to be an important structural factor enabling formation of spheres, for which dihedral angles >50° between the neighboring arylene moieties were required. A single microsphere with high sphericity exhibited whispering gallery mode (WGM) photoemission upon excitation with a focused laser. In this emission, sharp and periodic emission lines were superimposed on a broad photoemission spectrum. The WGM spectral profiles were very sensitive to the integrity of the spherical geometries and surface smoothness, which depends on the self-assembling condition as well as the structure of the polymer backbone. Microspherical optical resonators consisting of such highly fluorescent conjugated polymers are novel. They also present advantages in that (i) there is no need for a light waveguide and fluorescent-dye doping, (ii) its high refractive index is beneficial for light confinement, and (iii) the fabrication process is simple, not requiring sophisticated, costly microfabrication technology

Conjugated Polymer Blend Microspheres for Efficient, Long-Range Light Energy Transfer

Highly luminescent π-conjugated polymeric microspheres were fabricated through self-assembly of energy-donating and energy-accepting polymers and their blends. To avoid macroscopic phase separation, the nucleation time and growth rate of each polymer in the solution were properly adjusted. Photoluminescence (PL) studies showed that efficient donor-to-acceptor energy transfer takes place inside the microspheres, revealing that two polymers are well-blended in the microspheres. Focused laser irradiation of a single microsphere excites whispering gallery modes (WGMs), where PL generated inside the sphere is confined and resonates. The wavelengths of the PL lines are finely tuned by changing the blending ratio, accompanying the systematic yellow-to-red color change. Furthermore, when several microspheres are coupled linearly, the confined PL propagates the microspheres through the contact point, and a cascade-like process converts the PL color while maintaining the WGM characteristics. The self-assembly strategy for the formation of polymeric nano- to microstructures with highly miscible polymer blends will be advantageous for optoelectronic and photonic device applications