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2005
Conducting metallopolymers: the roles of molecular architecture and redox matching.
Chemical Communications,p.23–36,2005Recent reports of highly conductive metallopolymers are reviewed. This literature is classified into one of two categories (inner or outer sphere) depending on the mode of interaction between the transition metal centers with each other and the conducting polymer backbone. The critical nature of charge transport is discussed in the context of the relative energies of the organic polymer-based and metal-centered redox processes. Also included are recent advances in the development of functional materials based on metal-containing conducting polymers. -
2005
Amplifying fluorescent polymer sensors for the explosives taggant 2,3-dimethyl-2,3-dinitrobutane (DMNB).
Chemical Communications,p.4572–4,2005Structural and electronic effects on the efficiency of DMNB detection with fluorescent conjugated polymers are described. -
2005
Insulated conducting polymers: manipulating charge transport using supramolecular complexes.
Chemical Communications,p.5211–5213,2005Rotaxane structures which provide functional insulation to conducting polymers can provide over a 4000-fold redn. in cond. over non-rotaxane structures and with electronically active copper ions in the rotaxane units the cond. increases by more than 80 times relative to the metal-free analog. [on SciFinder(R)] -
2005
Phase and orientational ordering of A–B–A tri-block co-polymers guest in a quenched host of low molecular weight rod molecules
Chemical Physics Letters,vol.408,p.139–144,2005We investigate the effects of thermodynamical variables, intermol. interactions and block lengths on phase and orientational ordering of guest tri-block co-polymers in a host glassy matrix of short mol. rods. The A and B blocks can align to the short rod mols. Using a field theoretic formulation we demonstrate the occurrence of a nematic-nematic (N/N) first order transition from a guest stabilized to a guest-host stabilized region, a reentrant transition from a guest stabilized nematic region to a host only stabilized regime via an isotropic phase and the possibility to selectively stabilize the orientation of the A or/and B blocks. [on SciFinder(R)] -
2005
Toward Isolated Molecular Wires: A pH-Responsive Canopied Polypyrrole
Chemistry of Materials,vol.17,p.4622–4629,2005The design, synthesis, and electropolymn. of sterically hindered pyrrole derivs. are described. Endo and exo adducts of cyclopentadiene and N-phenylmaleimide were converted to give bicyclo[2.2.1]heptane-fused pyrrole monomers, in which a Ph group is rigidly placed proximate the pyrrole fragment. Oxidative polymn. of these monomers affords highly conductive polypyrroles. The rigid mol. scaffold of the pyrrole monomers limits cross-communication between adjacent conducting strands and produces a defined narrow potential window of high cond. dominated by intrachain polaronic charge carriers. The resultant loosely packed polymer chains allow for superior sensory properties. Notably, the elec. cond. of oxidatively doped poly(7) could be reversibly modulated in aq. electrolytes at pH 3-9. [on SciFinder(R)] -
2005
Detection of myelination using a novel histological probe.
Journal of Histochemistry and Cytochemistry,vol.53,p.1511–6,2005Current methods for myelin staining in tissue sections include both histological and immunohistochemical techniques. Fluorescence immunohistochemistry, which uses antibodies against myelin components such as myelin basic protein, is often used because of the convenience for multiple labeling. To facilitate studies on myelin, this paper describes a quick and easy method for direct myelin staining in rodent and human tissues using novel near-infrared myelin (NIM) dyes that are comparable to other well-characterized histochemical reagents. The near-infrared fluorescence spectra of these probes allow fluorescent staining of tissue sections in multiple channels using visible light fluorophores commonly used in immunocytochemistry. These dyes have been used successfully to detect normal myelin structure and myelin loss in a mouse model of demyelination disease. -
2005
Towards chemosensing phosphorescent conjugated polymers: cyclometalated platinum(II) poly(phenylene)s
Journal of Materials Chemistry,vol.15,p.2829,2005The synthesis and optical properties of several phosphorescent conjugated poly(phenylene)s contg. cyclometalated square-planar platinum (II) complexes are reported. These electronic polymers were synthesized via Suzuki cross-coupling of a dibromophenylpyridine-ligated Pt(ii) complex with a fluorene diboronic ester. Their optical properties are characterized by relatively strong orange room-temp. phosphorescence with well-resolved vibronic structure in both frozen 2-methyltetrahydrofuran glass and room-temp. fluid soln. Time-resolved phosphorescence spectroscopy has shown that the polymers have excited state lifetimes of approx. 14 $μ$s. These optical properties of the oligomers and polymers are contrasted with those of small model complexes, the optical properties of which have a strong dependence on the identity of the $\beta$-diketonate ligand used. The potential utility of phosphorescent conjugated polymers is illustrated by examn. of the diffusive quenching due to oxygen as a function of mol. structure. [on SciFinder(R)] -
2005
Intramolecular photoinduced charge transfer in rotaxanes.
Journal of the American Chemical Society,vol.127,p.5902–9,2005We report the synthesis and photophysical investigation of a series of rotaxanes in which the physical confinement of the donor and acceptor (DA) pair leads, in some cases, to emissive exciplexes. As a comparison, we examined the photoinduced charge-transfer processes in the same DA mixtures under intermolecular conditions. The interlocked configuration of the rotaxane facilitates pi orbital overlap of the excited state DA pair by keeping their center-to-center distance extremely small. This increased interaction between the DA pair significantly lowers the activation energy for exciplex formation (E(a)) and helps stabilize the highly polar charge-transfer complex. We find that the stabilizing effect of the rotaxane architecture compensates for the modest thermodynamic driving force for some charge-transfer interactions. In addition, we examined the temperature dependence on the rotaxanes’ optical properties. Metal coordination to the tetrahedral cavity disrupts the cofacial conformation of the DA pair and quenches the fluorescence. Binding of alkali metal ions to the 3,4-ethylenedioxythiophene (EDOT)-based rotaxane, however, gives rise to the emergence of a new weak emission band at even lower energies, indicative of a new emissive exciplex. -
2005
Synthesis and application of poly(phenylene ethynylene)s for bioconjugation: a conjugated polymer-based fluorogenic probe for proteases.
Journal of the American Chemical Society,vol.127,p.3400–5,2005A set of carboxylate-functionalized poly(phenylene ethynylene)s (PPEs) has been synthesized in which the carboxylic acid groups are separated from the polymer backbone by oligo(ethylene glycol) spacer units. These polymers are soluble in water and organic solvents and have photophysical properties that are sensitive to solvent conditions, with high salt content and the absence of surfactant promoting the formation of aggregates of relatively low quantum yield and long fluorescence lifetime. Quenching of these materials by the dinitrophenyl (DNP) chromophore (K(SV) approximately 10(4)) is also highly solvent-dependent. The presence of carboxylate groups far from the polymer backbone appended to each repeating unit allows for the postpolymerization modification of these PPEs with peptides by methods analogous to those described for carboxylate-functionalized small-molecule dyes. Covalent attachment of the fluorescence-quenching 14-mer Lys(DNP)-GPLGMRGLGGGGK to the PPE results in a nonemissive substrate whose fluorescence is restored upon treatment with trypsin. The rate of fluorescence turn-on in this case is increased 3-fold by the presence of surfactant, though the actual rate of peptide hydrolysis remains the same. A small-molecule mimic of the polymer-peptide system shows a smaller fluorescence enhancement upon treatment with trypsin, illustrating the value of polymer-based amplification in this sensory scheme. -
2005
perpendicular organization of macromolecules: synthesis and alignment studies of a soluble poly(iptycene).
Journal of the American Chemical Society,vol.127,p.17976–7,2005We describe herein a polymeric material that prefers to align perpendicular to a stretch-aligned polymer host in the solid state. Poly(iptycene) poly-1 was synthesized from monomer 1 under hyperbaric techniques via a Diels-Alder polymerization. Polarized excitation spectra of the anthracene end groups in this material in a stretch-aligned, solution-cast poly(vinyl chloride) (PVC) film showed that the poly(iptycene) prefers to align normal (counter aspect ratio) to the stretching direction of the PVC. This is explained by a \”threading\” mechanism, whereby the PVC intercalates through the internal free volume presented by poly-1, similar to effects observed in small molecule iptycenes under similar conditions. -
2005
Highly emissive conjugated polymer excimers.
Journal of the American Chemical Society,vol.127,p.13726–31,2005Conjugated polymers often display a decrease of fluorescence efficiency upon aggregation due in large part to enhanced interpolymer interactions that produce weakly emissive species generally described as having excimer-like character. We have found that poly(phenylene ethynylene)s with fused pendant [2.2.2] ring structures having alkene bridges substituted with two ester groups function to give highly emissive, broad, and red-shifted emission spectra in the solid state. To best understand the origin of this new solid-state emissive species, we have performed photophysical studies of a series of different materials in solution, spin-coated thin films, solid solutions, and Langmuir films. We conclude that the new, red-shifted, emissive species originate from excimers produced by interchain interactions being mediated by the particular [2.2.2] ring system employed. The ability to design structures that can reliably produce highly emissive conjugated polymer excimers offers new opportunities in the emission tailoring of electroluminescence and sensory devices. -
2005
High ionization potential conjugated polymers.
Journal of the American Chemical Society,vol.127,p.12122–30,2005We report the synthesis of a series of poly(p-phenylene ethynylene)s (PPEs) with high ionization potentials and associated high excited-state electron affinities. Their photophysical properties were investigated using steady-state and time-resolved fluorescence techniques. The ionization potentials of the polymer thin films were determined using ultraviolet photoelectron spectroscopy (UPS), and those with the highest ionization potentials displayed high sensitivity for the detection of electron-donating aromatic compounds. The effects of sterics, chemical structure, and electronic properties on the polymers’ sensory responses were investigated by fluorescence quenching experiments in both solution and solid thin films. In addition, we report that in some cases the excited-state charge-transfer complexes (exciplexes) of the PPEs with analytes were observed. These latter effects provide promising opportunities for the formation of sensitive and selective chemical sensors. -
2005
Conjugation enhancement of intramolecular exciton migration in poly(p-phenylene ethynylene)s.
Journal of the American Chemical Society,vol.127,p.10083–8,2005Efficient energy migration in conjugated polymers is critical to their performance in photovoltaic, display, and sensor devices. The ability to precisely control the polymer conformation is a key issue for the experimental investigations and deeper understanding of the nature of this process. We make use of specially designed iptycene-containing poly(p-phenylene ethynylene)s that display chain-extended conformations when dissolved in nematic liquid crystalline solvents. In these solutions, the polymers show a substantial enhancement in the intrachain exciton migration rate, which is attributed to their increased conjugation length and better alignment. The organizational enhancement of the energy transfer efficiency, as determined by site-selective emission from lower energy traps at the polymer termini, is accompanied by a significant increase of the fluorescence quantum yield. The liquid crystalline phase is a necessary requirement for these phenomena to occur, and when the temperature was increased above the nematic-isotropic transition, we observed a dramatic reduction of the energy transfer efficiency and fluorescence quantum yield. The ability to improve the exciton migration efficiency through precise control of the polymer structure with liquid crystalline solutions demonstrates the importance of a polymer’s conformation for energy transfer, and provides a way to improve the energy transporting performance of conjugated polymers. -
2005
Effect of thick anisotropic NLC layer on lasing in polymeric cholesteric liquid crystals.
Journal of the Korean Physical Society,vol.46,p.S265–S268,2005We have studied the lasing characteristics from a dye-doped nematic liq. crystal layer sandwiched by two polymeric cholesteric liq. crystal films as photonic band gap materials. The nematic layer possessing birefringence brings about the following remarkable optical characteristics: (1) reflectance in the photonic band-gap (PEG) region exceeds 50 %, due to the retardation effect, being unpredictable from a single CLC film; (2) efficient lasing occurs at the notch of PEG; (3) the lasing emissions contain both right- and left-circular polarizations. In this study, we demonstrate that a 100-$μ$m-thick nematic liq. crystal layer system shows several dips, resulting in multi-mode lasing actions just at the dips within PBG. [on SciFinder(R)] -
2005
Sensory Responses in Solution vs Solid State: A Fluorescence Quenching Study of Poly(iptycenebutadiynylene)s
Macromolecules,vol.38,p.9377–9384,2005A new series of poly(p-phenylenebutadiynylene)s has been synthesized with unique polymer structural features. In these systems each of the p-phenylene units in the conjugated backbone is the core of a rigid three-dimensional iptycene scaffold. The fluorescence quenching properties of these polymers in response to a series of electron-deficient arom. compds. have been investigated in both soln. and the solid state. It was found that in soln. these polymers displayed higher quenching sensitivity toward studied quenchers compared to a more open-structure iptycene-contg. poly(p-phenyleneethynylene). The quenching behaviors of the conjugated polymer were shown to be strongly influenced by the configuration of the incorporated iptycences. The thin films investigations revealed differences in both the fluorescence quenching and the recovery processes. Distinct behaviors indicated that the fluorescence quenching in the solid state is dictated by different factors than those in soln. Our results further suggest that poly(p-phenylenebutadiynylene)s contg. large iptycene scaffolds that introduce porosity have the ability to efficiently sequester the quencher mols. within thin films as these materials display slow fluorescence recoveries. [on SciFinder(R)] -
2005
Synthesis and Properties of Poly(phenylene ethynylene)s with Pendant Hexafluoro-2-propanol Groups
Macromolecules,vol.38,p.9091–9094,2005Several poly(phenylene-ethynylene)s with pendant hexafluoro-2-propanol (HFIP) groups have been synthesized and characterized in terms of their soln. and thin-film optical properties. The incorporation of strongly hydrogen-bond-donating HFIP groups into conjugated polymers is shown to greatly enhance their fluorescence response upon exposure to the vapors of several hydrogen-bond-accepting analytes such as pyridine and 2,4-dichloropyrimidine. The enhanced sensitivity of these conjugated polymer-based chemosensors is the result of stronger analyte/polymer binding interactions and more facile photoinduced charge-transfer reactions with hydrogen-bonded analytes. [on SciFinder(R)] -
2005
Layer-by-Layer Poly(phenylene ethynylene) Films on Silica Microspheres for Enhanced Sensory Amplification
Macromolecules,vol.38,p.9287–9290,2005Alternating polyelectrolyte “layer-by-layer” deposition was used to create emissive thin films of a weakly anionic, nonaggregating poly(phenylene ethynylene) on silica microspheres. The resulting particles are smooth and emit fluorescence solely from the outside polymer-coated surface. Suspensions of the coated microspheres show similar fluorescence properties to polymers in soln., but with enhanced sensitivity (up to 200-fold) to nitroarom. quenchers. These enhancements are attributed to a combination of surface and electronic effects. [on SciFinder(R)] -
2005
Highly Conductive Poly(phenylene thienylene)s: m -Phenylene Linkages Are Not Always Bad
Macromolecules,vol.38,p.4569–4576,2005Two isomeric polymers, which contain meta- or para-phenylene linkages between conducting segments, were synthesized and compared by electrochem. methods. The nonconjugated poly(1,5-diacetoxy-m-phenylene tetrathienylene) (PMPT-OAc) showed similar electroactivity to the para-isomer, poly(2,5-diacetoxy-p-phenylene tetrathienylene) (PPPT-OAc), in the cyclic voltammetry and in-situ cond. measurements. Spectroelectrochem. showed a similar buildup of sub-band-gap electronic transitions. Deacetylation of the polymers was performed successfully by reaction with hydrazine, producing PMPT-OH and PPPT-OH. Both phenol-substituted polymers exhibited greater electroactivity than the acetoxy-substituted polymers. In addn., the phenol substituents were found to lower the “turn-on” potential in the cond.-potential profile for PMPT-OH, but not for PPPT-OH. An alkoxy-substituted PMPT-OMe shows electroactivity similar to that of PMPT-OAc in the cyclic voltammetry, in-situ cond., and spectroelectrochem. [on SciFinder(R)] -
2005
Facile Control of Chiral Packing in Poly( p -phenylenevinylene) Spin-Cast Films
Macromolecules,vol.38,p.4054–4057,2005CD spectroscopy was used to demonstrate that a film spin-cast from a polymer having a polyphenylenevinylene backbone and enantiomerically pure chiral side chains can be fabricated from different solvents to have correspondingly different chiral architectures with opposite handedness. [on SciFinder(R)] -
2005
Synthesis and Optical Properties of Simple Amine-Containing Conjugated Polymers
Macromolecules,vol.38,p.2716–2721,2005Conjugated polymers (CPs) contg. amino groups have been synthesized, and their optical properties in both soln. and thin film have been studied. New monomers required for the synthesis of these polymers have been readily prepd. via efficient synthetic routes. These monomers have been successfully polymd. with a variety of comonomers. The spectral positions of the absorption and emission spectra correlate with the degree of electron d. on the polymer chain. Polymers contg. N-alkylcarbazole units display similar optical properties in soln. to most CPs. Polymers with dialkylamino groups, however, display very different optical properties, including broadened absorbance and emission spectra, larger Stokes shifts, and longer excited state lifetimes. These results are consistent with a significant difference between the mol. geometries of the absorbing and emitting states. The solid state emission of most of the polymers is sufficient to warrant them for consideration as fluorescent sensing materials. [on SciFinder(R)]
