Poly(aryleneethynylene)s

Oligo(phenyleneethynylene)s: Shape-Tunable Building Blocks for Supramolecular Self-Assembly

Oligo(phenyleneethynylene)s (OPEs) have attracted widespread attention due to their remarkable (opto)electronic and photophysical properties, which have enabled numerous applications. The versatile functionalization possibilities of OPEs make them unique candidates to form various shape-persistent geometries, including linear, triangular, rectangular, hexagonal and macrocyclic. However, as a result of this structural variety, it is oftentimes challenging to correlate molecular design with self-assembly properties. In this minireview, we have classified OPEs based on their molecular shapes and correlated them with their self-assembly behavior in solution. Particularly, we provide important insights into the aggregation propensity of the different molecular shapes and how to tune the association strength using various non-covalent interactions. Our classification will enable a better understanding of the structure-property correlation in OPEs, which is key to develop supramolecular functional materials.

Polydots, soft nanoparticles, at membrane interfaces

Soft nanoparticles (NPs) are emerging candidates for nano medicine, particularly for intercellular imaging and targeted drug delivery. Their soft nature, manifested in their dynamics, allows translocation into organisms without damaging their membranes. A crucial step towards incorporating soft dynamic NPs in nano medicine, is to resolve their interrelation with membranes. Here using atomistic molecular dynamics (MD) simulations we probe the interaction of soft NPs formed by conjugated polymers with a model membrane. These NPs, often termed polydots, are confined to their nano dimensions without any chemical tethers, forming dynamic long lived nano structures. Specifically, polydots formed by dialkyl para poly phenylene ethylene (PPE), with a varying number of carboxylate groups tethered to the alkyl chains to tune the interfacial charge of the surface of the NP are investigated at the interface with a model membrane that consists of di-palmitoyl phosphatidylcholine (DPPC). We find that even though polydots are controlled only by physical forces, they retain their NP configuration as they transcend the membrane. Regardless of their size, neutral polydots spontaneously penetrate the membrane whereas carboxylated polydots must be driven in, with a force that depends on the charge at their interface, all without significant disruption to the membrane. These fundamental results provide a means to control the position of the nanoparticles with respect to the membrane interfaces, which is key to their therapeutic use.

Advances in the application of named reactions in polymer synthesis

With the development of polymer science, more and more named reactions have been applied to synthesizing polymers. Introducing new reactions into polymer synthesis is undoubtedly an excellent expansion for monomer and polymer libraries. In this review, the named reactions employed in polymer-chain synthesis were divided into seven types: electrophilic reactions, nucleophilic reactions, transition metal-mediated cross-coupling reactions, free radical reactions, pericyclic reactions, multi-component reactions and rearrangement reactions. The discussion was mainly focused on the progress in the utilization of these named reactions in polymer synthesis, which could be a valuable reference for researchers in the polymer field.

Vibrations Responsible for Luminescence from HJ-Aggregates of Conjugated Polymers Identified by Cryogenic Spectroscopy of Single Nanoparticles

A single polymer chain can be thought of as a covalently bound J-aggregate, where the microscopic transition-dipole moments line up to emit in phase. Packing polymer chains into a bulk film can result in the opposite effect, inducing H-type coupling between chains. Cofacial transition-dipole moments oscillate out of phase, canceling each other out, so that the lowest-energy excited state turns dark. H-aggregates of conjugated polymers can, in principle, be coaxed into emitting light by mixing purely electronic and vibronic transitions. However, it is challenging to characterize this electron-phonon coupling experimentally. In a bulk film, many different conformations exist with varying degrees of intrachain J-type and interchain H-type coupling strengths, giving rise to broad and featureless aggregate absorption and emission spectra. Even if single nanoparticles consisting of only a few single chains are grown in a controlled fashion, the luminescence spectra remain broad, owing to the underlying molecular dynamics and structural heterogeneity at room temperature. At cryogenic temperatures, emission from H-type aggregates should be suppressed because, in the absence of thermal energy, internal conversion drives the aggregate to the lowest-energy dark state. At the same time, electronic and vibronic transitions narrow substantially, facilitating the attribution of spectral signatures to distinct vibrational modes. We demonstrate how to distinguish signatures of interchain H-type aggregate species from those of intramolecular J-type coupling. Whereas all dominant vibronic modes revealed in the photoluminescence (PL) and surface-enhanced resonance Raman scattering spectra of a single chromophore within a single polymer chain are identified in the J-type aggregate luminescence spectra, they are not all present at once in the H-type spectra. Universal spectral features are found for the luminescence from strongly HJ-coupled chains, clearly resolving the vibrations responsible for the nonadiabatic excited-state molecular dynamics that enable light emission. We discuss the possible combinations of vibrational modes responsible for H-type aggregate PL and demonstrate that only one, mainly the lowest energy one, of the three dominant vibrational modes contributes to the 0-1 transition, whereas combinations of all three are found in the 0-2 transition. From this analysis, we can distinguish between energy shifts due to either J-type intrachain coupling or H-type interchain interactions, offering a means to directly discriminate between structural and energetic disorder.

Self-assembled organic and hybrid materials derived from oligo-(p-phenyleneethynylenes)

Oligo-(p-Phenyleneethynylenes) (OPEs) have garnered widespread interest over the past three decades due to their excellent opto-electronic properties. However, the chief focus has been on the use of mainly small molecules or polymeric systems for the study of their structural diversity in opto-electronic applications. Recently, researchers have started delving deeper into their utility in material applications. Purely organic materials such as supramolecular polymers, self-assembled nanostructures, nanostructured organogels and single-crystalline materials derived from OPEs have already been developed and researched. Chirality has also been introduced into these systems. Additionally, these have shown physical properties such as polymorphism, liquid crystallinity, melt formation, mechanochromism, etc. All these materials have also shown excellent luminescence properties with high quantum yield and some have even shown energy harvesting properties. There have also been sporadic reports on OPE linker based hybrid systems such as metallogels and metal-organic framework (MOF) structures where structural analysis reveals the origin of tunable emission in these materials. Furthermore, by innovative structural design, unexplored properties of OPEs such as water repellency, bioimaging, drug delivery, photocatalysis, energy transfer, nanomorphology control, photoconductivity, and colour tunability could be achieved. This feature article will, therefore, encompass a detailed discussion on the development of this field as well as the analysis of the properties realized in OPE derived self-assembled supramolecular materials. The main focus will be on the following classes of materials: soft supramolecular materials, crystalline supramolecular π-systems, nanoscale metal-organic frameworks (NMOFs) and bulk metal-organic frameworks (MOFs) and how their application horizon has been expanded by integrating OPEs into their structures.

Chromatic Conductive Polymer Nanocomposites of Poly (p-Phenylene Ethynylene)s and Single-Walled Carbon Nanotubes

We report on dispersions and thin films of chromatic conductive nanocomposites of poly(p-phenylene ethynylene)s (PPEs) and single-walled carbon nanotubes (SWNTs) generated via solution mixing. The linear, conjugated PPEs with dialkyl- and dialkyloxy-side chain groups are shown to debundle and disperse high concentration (up to 2.5 mg/mL) SWNTs in various organic solvents. The solubilization of SWNTs and PPE wrapping is accompanied with the change in the solution color. Ultraviolet visible absorption spectra of nanocomposite solutions demonstrate a new absorption peak at a higher wavelength, supporting the observed chromatism. Fluorescence spectra of nanocomposite solutions display significant quenching of the fluorescence intensity and the Stern–Volmer model is used to analyze fluorescence quenching. Electron microscopy of the chromatic solid films of high mass fraction PPE/SWNT nanocomposites obtained by vacuum filtration reveals the debundled SWNTs in the PPE matrix. The tensile strength and Young’s modulus of these PPE/SWNT nanocomposite films are as high as 150 MPa and 15 GPa, respectively. The composite films exhibit remarkably high conductivities, ranging from ~1000 S/m to ~10,000 S/m for 10 wt% and 60 wt% SWNT nanocomposites, respectively.

Periodic Fluorescence Variations of CdSe Quantum Dots Coupled to Aryleneethynylenes with Aggregation-Induced Emission

CdSe nanocrystals and aggregates of an aryleneethynylene derivative are assembled into a hybrid thin film with dual fluorescence from both fluorophores. Under continuous excitation, the nanocrystals and the molecules exhibit anticorrelated fluorescence intensity variations, which become periodic at low temperature. We attribute this to a structure-dependent aggregation-induced emission of the aryleneethynylene derivative, which impacts the rate of excitation energy transfer between the molecules and nanocrystals. This work highlights that combining semiconductor nanocrystals with molecular aggregates, which exhibit aggregation-induced emission, can result in emerging optical properties.

Near-Infrared Fluorescent Probes with Rotatable Polyacetylene Chains for the Detection of Amyloid-β Plaques

The plaques of accumulated β-amyloid (Aβ) in the parenchymal brain are accepted as an important biomarker for the early diagnosis of Alzheimer's disease (AD). Many near-infrared (NIR) probes, which were based on the D-π-A structure and bridged by conjugated double bonds, had been reported and displayed a high affinity to Aβ plaques. Considering the isomerization caused by the polyethylene chain, however, the conjugated polyacetylene chain is a better choice for developing new NIR Aβ probes. Hence, in this report, a new series of NIR probes with naphthyl or phenyl rings and different numbers of conjugated triple bonds were designed, synthesized, and evaluated as NIR probes for Aβ plaques. Upon interaction with Aβ aggregates, these probes displayed a significant increase in fluorescence intensity (45- to 360-fold) and a high to moderate affinity (6.05-56.62 nM). Among them, probe 22b displayed excellent fluorescent properties with a 183-fold increase in fluorescence intensity and an emission maximum at 650 nm after incubated with Aβ aggregates. Furthermore, 22b had a high affinity to Aβ aggregates (K_d = 12.96 nM) and could efficiently detect the Aβ plaques in brain sections from both transgenic mice and AD patients in vitro. In summary, this work may lead to a new direction in the development of novel NIR probes for the detection of Aβ plaques.

Emergence of uniform tilt and π-stacking in triangular liquid crystalline honeycombs

The synclinic tilted organization of specifically designed polyphilic oligo(p-phenylene ethynylene) rods in cylindrical shells around triangular prismatic cells on the <5 nm scale leads to a new kind of liquid crystalline honeycomb composed of helical shells with alternating helix sense. Core fluorination at the outer ring modifies the core-core interactions, thus resulting in triangular arrays with face-to-face π-stacking along the honeycomb.

Multicomponent Polymerization for π-Conjugated Polymers

Structurally complex π-conjugated polymers hold great promise as key components in sensor and electronic devices; however, their syntheses have not been a trivial task. From a synthetic efficiency perspective, it would be more attractive to access these materials using convenient and efficient methods from simple building blocks. One such synthetic tool, multicomponent polymerization, can accommodate modularity and provide highly efficient syntheses. This feature article outlines several multicomponent polymerization strategies for the synthesis of various π-conjugated polymers, which are classified based upon how the monomers are aligned during polymerization. Additionally, the challenges and outlooks of this field are highlighted and discussed.

Chiroptical Properties in Thin Films of π-Conjugated Systems

Chiral π-conjugated molecules provide new materials with outstanding features for current and perspective applications, especially in the field of optoelectronic devices. In thin films, processes such as charge conduction, light absorption, and emission are governed not only by the structure of the individual molecules but also by their supramolecular structures and intermolecular interactions to a large extent. Electronic circular dichroism, ECD, and its emission counterpart, circularly polarized luminescence, CPL, provide tools for studying aggregated states and the key properties to be sought for designing innovative devices. In this review, we shall present a comprehensive coverage of chiroptical properties measured on thin films of organic π-conjugated molecules. In the first part, we shall discuss some general concepts of ECD, CPL, and other chiroptical spectroscopies, with a focus on their applications to thin film samples. In the following, we will overview the existing literature on chiral π-conjugated systems whose thin films have been characterized by ECD and/or CPL, as well other chiroptical spectroscopies. Special emphasis will be put on systems with large dissymmetry factors (g_abs and g_lum) and on the application of ECD and CPL to derive structural information on aggregated states.

A periodic dodecagonal supertiling by self-assembly of star-shaped molecules in the liquid crystalline state

Molecular tessellations are known in solid state systems and their formation is often induced or supported by a periodic surface lattice. Here we discover a complex tessellation on the 10 nm length scale, spontaneously formed in the highly dynamic liquid crystalline state. It is composed of overlapping dodecagonal supertiles combining prismatic cells with triangular and square cross sections. This complex honeycomb occurs between a triangular honeycomb at high and a square at low temperature, being opposite to the sequence expected for a thermal expansion of the side chains in the prismatic cells. Formation of the supertiles is supported by the segregation of alkyl chains with different length. The emergent behaviour of this complex soft matter structure is demonstrated, and intriguing connections between self-assembly on surfaces, in liquid crystals, and in block copolymers are drawn. Moreover, the tessellation represents a close approximant of the elusive columnar liquid quasicrystal with dodecagonal symmetry.

pH-Responsive Side Chains as a Tool to Control Aqueous Self-Assembly Mechanisms

pH-Tunable nanoscale morphology and self-assembly mechanism of a series of oligo(p-phenyleneethynylene) (OPE)-based bolaamphiphiles featuring poly(ethylene imine) (PEI) side chains of different length and degree of hydrolysis are described. Protonation and deprotonation of the PEI chains by changing the pH alters the hydrophilic/hydrophobic balance of the systems and, in turn, the strength of intermolecular interactions between the hydrophobic OPE moieties. Low pH values (3) lead to weak interaction between the OPEs and result in spherical nanoparticles, in which aggregation follows an isodesmic mechanism. In contrast, higher pH values (11) induce deprotonation of the polymer chains and lead to a stronger, cooperative aggregation into anisotropic nanostructures. Our results demonstrate that pH-responsive chains can be exploited as a tool to tune self-assembly mechanisms, which opens exciting possibilities to develop new stimuli-responsive materials.

On-surface synthesis of graphyne nanowires through stepwise reactions

We have achieved on-surface synthesis of graphyne nanowires through stepwise reactions involving two different types of dehalogenative homocoupling reactions (i.e., C(sp³)–Br and C(sp²)–Br).

Discrete boronate ester ladders from the dynamic covalent self-assembly of oligo(phenylene ethynylene) derivatives and phenylenebis(boronic acid)

Reversible boronate ester chemistry enables the controlled, dynamic self-assembly of olig(phenylene ethynylene)s into highly conjugated ladder frameworks.

Rod-like transition first or chain aggregation first? ordered aggregation of rod-like poly(p-phenyleneethynylene) chains in solution

The rod-like configuration of conjugated polymer chains with its low energetic disorder is the key to utilizing the backbone as a highly electrically-conductive wire. An energetic disorder that is higher than 0.1 eV, coupled with vibronic modes of the chains, leads to the localization of charges. Herein, we have tracked precisely the rod-like transition of poly(p-phenyleneethynylene) (PPE) chains as a function of temperature in diluted solutions, and shown a steep increase in persistence length at 230 K. The resulting rod-like configuration of the PPE chains with its extended electronic conjugation exhibited an extremely small energetic disorder of ∼70 meV, and was stabilized by subsequent polymer aggregate formation.

Homo-FRET in π-Conjugated Polygons: Intermediate-Strength Dipole-Dipole Coupling Makes Energy Transfer Reversible

The concept of homo-FRET is often used to describe energy transfer between like chromophores of molecular aggregates such as in π-conjugated polymers. Homo-FRET is revealed by a dynamic depolarization in fluorescence but strictly only applies to the limit of weak dipole-dipole coupling, where energy transfer occurs on time scales much longer than those of nuclear relaxation. By considering the polarization anisotropy of photoluminescence emission and excitation of model multichromophoric aggregates on the single-molecule level, we demonstrate the transition of energy-transfer dynamics from the case of weak coupling to that of strong coupling, revealing the elusive regime of intermediate-strength coupling where energy transfer between degenerate donor and acceptor chromophores becomes reversible so that information on the excitation route of the emitting chromophore is lost.

Soft self-assembled sub-5 nm scale chessboard and snub-square tilings with oligo(para-phenyleneethynylene) rods

X-Shaped bolapolyphiles, comprising a linear polyaromatic core with glycerol groups at each end and two chemically different and incompatible chains, fixed to it at opposite sides, were synthesized and found to self-assemble into honeycomb-type liquid crystalline phases with square symmetry. The polyaromatic π-conjugated rods form the cell walls and the resulting prismatic cells of sub-5 nm size are alternatively filled with perfluorocarbon (RF) and the carbosilane chains (RSi). The resulting structures can be represented as either a two-colour snub-square tiling with triangular and square cells or as a chessboard tiling of squares.

Interplay between H-Bonding and Preorganization in the Evolution of Self-Assembled Systems

Cooperative π-π interactions and H-bonding are frequently exploited in supramolecular polymerization; however, close scrutiny of their mutual interplay has been largely unexplored. Herein, we compare the self-assembly behavior of a series of C2 - and C3 -symmetrical oligophenyleneethynylenes differing in their amide topology (N- or C-centered). This subtle structural modification brings about drastic changes in their photophysical and supramolecular properties, highlighting the reciprocal impact of H-bonding vs. preorganization on the evolution and final outcome of supramolecular systems.

Printing Poly( p-phenyleneethynylene) PLEDs

Gravure printing of functional thin-film layers of side-chain-substituted poly( para-phenyleneethynylene)s (PPEs) is reported. Rheological properties of PPEs in combination with the Hansen solubility model allowed the formulation of enhanced single-component inks. Layer evaluation is performed with reflectometric thin-film recordings in an optical setup for laterally resolved large-area investigation using imaging color reflectometry. An organic light-emitting diode in a simple glass/indium tin oxide/poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)/PPE/LiF-Al stack was gravure-printed from the improved ink showing excellent luminance (542 cd m^-2, U = 11.5 V) for this polymer class.

Defining side chain successions in anthracene-based poly(arylene ethynylene)-alt-poly(phenylene vinylene)s: probing structure–property relationships

A detailed spectroscopic study of nine conjugated polymers with various octyloxy/2-ethylhexyloxy side chain sequences prepared using optimized regio-selective synthetic pathways.

Synthesis and photophysical properties of water-soluble fluorinated poly(aryleneethynylene)s

Reported are the synthesis of water-soluble fluorinated conjugated polymers, and photophysical properties, and fluorescence quenching response to arylamines.

Well-Defined Alkyne Metathesis Catalysts: Developments and Recent Applications

Although alkyne metathesis has been known for 50 years, rapid progress in this field has mostly occurred during the last two decades. In this article, the development of several highly efficient and thoroughly studied alkyne metathesis catalysts is reviewed, which includes novel well-defined, in situ formed and heterogeneous systems. Various alkyne metathesis methodologies, including alkyne cross-metathesis (ACM), ring-closing alkyne metathesis (RCAM), cyclooligomerization, acyclic diyne metathesis polymerization (ADIMET), and ring-opening alkyne metathesis polymerization (ROAMP), are presented, and their application in natural product synthesis, materials science as well as supramolecular and polymer chemistry is discussed. Recent progress in the metathesis of diynes is also summarized, which gave rise to new methods such as ring-closing diyne metathesis (RCDM) and diyne cross-metathesis (DYCM).

A Tethered Tolane: Twisting the Excited State

The synthesis of a doubly bridged tolane is reported. The target is obtained in a five-step synthesis, starting from commercially available 2-amino-meta-xylene by a combination of a Sandmeyer reaction, radical bromination, and Stille-type coupling, followed by double ring closing. The doubly tethered tolane is crystalline; the two phenyl rings are highly twisted with respect to each other both in solution and in the solid state. Optical spectroscopy and quantum chemical calculations show that the doubly bridged tolane is twisted not only in the ground state, but also in the excited state, leading to emission from the twisted state in solution and in the solid state. Strong phosphorescence is observed at cryogenic temperatures.

Ligand-Binding Ability of a Porphyrin Core in a Dendrimer with Rigid Branched Terminal Components

A dendrimer with rigid branched terminal components was prepared by a copper-catalyzed Hüisgen 1,3-dipolar cycloaddition reaction. A zinc 5,15-diethynyl-10,20-bis(3,5-di- tert-butylphenyl)porphyrin unit was incorporated at the core of the dendrimer as a receptor site for an added pyridyl ligand. The appearance of an absorption band characteristic of the planar conformer of conjugated chains in the terminal components suggested that the dendrimer adopts a folded higher order structure in dichloromethane at 25 °C. The binding constant between the zinc porphyrin core and a pyridyl ligand was evaluated by means of UV-vis absorption titration and compared with that of a suitable reference compound. The incorporation of the zinc porphyrin core into the folded dendrimer led to considerable suppression of its ligand-binding ability.

Rise of Conjugated Poly-ynes and Poly(Metalla-ynes): From Design Through Synthesis to Structure-Property Relationships and Applications

Conjugated poly-ynes and poly(metalla-ynes) constitute an important class of new materials with potential application in various domains of science. The key factors responsible for the diverse usage of these materials is their intriguing and tunable chemical and photophysical properties. This review highlights fascinating advances made in the field of conjugated organic poly-ynes and poly(metalla-ynes) incorporating group 4-11 metals. This includes several important aspects of conjugated poly-ynes viz. synthetic protocols, bonding, electronic structure, nature of luminescence, structure-property relationships, diverse applications, and concluding remarks. Furthermore, we delineated the future directions and challenges in this particular area of research.

Remarkable Amplification of Polyethylenimine-Mediated Gene Delivery Using Cationic Poly(phenylene ethynylene)s as Photosensitizers

Conjugated polymers can serve as good photosensitizers in biomedical applications. However, it remains unknown whether they are phototoxic to the supercoiled structure of DNA in improving gene delivery by the photochemical internalization (PCI) strategy, which complicates the application of conjugated polymers in gene delivery. In this work, we introduced a trace amount of cationic poly(phenylene ethynylene)s (cPPEs) into the polymeric shell of branched polyethylenimine (BPEI)/DNA complexes, studied the photosensitization of singlet oxygen by cPPEs, and confirmed that the supercoiled DNA is undamaged by the singlet oxygen generated by the photoexcitation of cPPEs. By taking advantage of the cPPE-mediated PCI effect, we report that the addition of the trace amount of cPPEs to the outer shell of the BPEI/DNA polyplexes could greatly amplify the transfection of gene green fluorescent protein on tumor cells with the efficiency from 14 to 86% without decreasing the cell viabilities, well solving the problem with a poor transfection capability of BPEI under low DNA-loading conditions. Our strategy to employ conjugated polymers as photosensitizing agents in gene delivery systems is simple, safe, efficient, and promising for broad applications in gene delivery areas.

Reversible mechanofluorochromism of aniline-terminated phenylene ethynylenes

Seven three-ring phenylene-ethynylene (PE) structural analogs, differing only in the lengths of alkyl chains on terminal aniline substituents, show 50-62 nm bathochromic shifts in emission maxima in response to mechanical force (mechanofluorochromism, MC). These shifts are fully reversible with heat or solvent fuming. Shearing of these solids yields a transition from green-emitting crystalline phases to orange-emitting amorphous phases as established by differential scanning calorimetry and X-ray diffraction. Molecules with shorter alkyl chain lengths required higher temperatures to recover the hypsochromically shifted crystalline phases after grinding, while the recovery with chain lengths longer than butyl occurred at room temperature. In addition to this structure-dependent thermochromism, these compounds retain their MC properties in polymer hosts to various extents. The crystalline phases of these materials have PE chromophores that are twisted due to non-covalent perfluoroarene-arene (ArF-ArH) interactions involving perfluorophenyl pendants and the terminal rings of the PE chromophore, resulting in interrupted conjugation and an absence of chromophore aggregation. The MC behavior of an analog without the perfluoroarene rings is severely attenuated. This work demonstrates the general utility of twisted PEs as stimuli-responsive moieties and reveals clear structure-property relationships regarding the effects of alkyl chain length on these materials.

Polymer Constructed Through the Formation of Carbon-Carbon Triple Bonds: Reductive Coupling Polymerization of Bis(benzylic gem-tribromide)s

Ethynylene-bridged polymers are currently synthesized by alkyne metathesis polymerization or Pd-catalyzed coupling between diethynylarene and dihaloarene. We report the formation of C≡C linkages in reductive coupling polymerization of bis(benzylic gem-tribromide)s promoted by Cu/polyamine under mild conditions. The polymer backbone was constructed through cascade formation of (Br)C═C(Br) bonds and C≡C bonds. This protocol provides a new method for synthesis of ethynylene-bridged polymers using monomers without alkynyl groups.

Fluorescence chemical sensor for determining trace levels of nitroaromatic explosives in water based on conjugated polymer with guanidinium side groups

A novel fluorescent conjugated polymer (poly(2-amino-N-(2-((4-ethynylphenyl) ethynyl) phenyl)-5-guanidinopentanamide)-1,4-phenylethynylene-1,4-phenyleneethynylene, PPE-Arg) was synthesized in this paper. We found that PPE-Arg could be quenched by picric acid (PA). Photoinduced electron transfer (PET) mechanism can be used to describe the fluorescence quenching of PPE-Arg. It could be speculated that the photo-induced electrons may be transferred from PPE-Arg to nitroaromatic explosives. In this paper, the experiment conditions and detection performance of PPE-Arg were systematically studied. The experiment results demonstrate PPE-Arg as a sensor for PA has a good linear range from 5 × 10^-7 to 6 × 10^-5 mol L^-1 with the calculated limit of detection (LOD) to be 1.0 × 10^-7 mol L^-1. Meanwhile, reaction time between PPE-Arg and PA is less than 1 min. This proposed sensor was applied to rapidly detect nitroaromatic explosives in environmental water samples and satisfactory results were obtained.

Molecular Wire Effects in Phenyleneethynylene Oligomers: Surprising Insights

The synthesis and quenching behavior of a series of water-soluble, carboxylate-carrying phenyleneethynylene oligomers-monomer to tetramer-and their polymers are reported; their quenching behavior with different test analytes (paraquat, lead salts, mercury salts, picric acid, methylpyridinium iodide) in water were investigated, and the results were compared to that of the conjugated polymer. Significant but analyte-dependent enhancement effects were found. For monovalent quenchers, only the molecular wire effect applies, but for divalent quenchers multivalency effects are also important.