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2005
Blue electroluminescence from oxadiazole grafted poly(phenylene-ethynylene)s.
Nano letters,vol.5,p.1597–601,2005Blue poly(phenylene-ethynylene) (PPE) electroluminescence is achieved in a single layer organic light emitting device. The polymeric system consists of an oxadiazole grafted PPE, which combines the necessary charge transport properties while maintaining the desirable efficient, narrow light-emitting properties of the PPE. Incorporation of a pentiptycene scaffold within the PPE structure prevents ground-state and excited-state interactions between the pendent oxadiazole units and the conjugated backbone. -
2005
Sensitivity gains in chemosensing by lasing action in organic polymers.
Nature,vol.434,p.876–9,2005Societal needs for greater security require dramatic improvements in the sensitivity of chemical and biological sensors. To meet this challenge, increasing emphasis in analytical science has been directed towards materials and devices having highly nonlinear characteristics; semiconducting organic polymers (SOPs), with their facile excited state (exciton) transport, are prime examples of amplifying materials. SOPs have also been recognized as promising lasing materials, although the susceptibility of these materials to optical damage has thus far limited applications. Here we report that attenuated lasing in optically pumped SOP thin films displays a sensitivity to vapours of explosives more than 30 times higher than is observed from spontaneous emission. Critical to this achievement was the development of a transducing polymer with high thin-film quantum yield, a high optical damage threshold in ambient atmosphere and a record low lasing threshold. Trace vapours of the explosives 2,4,6-trinitrotoluene (TNT) and 2,4-dinitrotoluene (DNT) introduce non-radiative deactivation pathways that compete with stimulated emission. We demonstrate that the induced cessation of the lasing action, and associated sensitivity enhancement, is most pronounced when films are pumped at intensities near their lasing threshold. The combined gains from amplifying materials and lasing promise to deliver sensors that can detect explosives with unparalleled sensitivity. -
2005
Conjugated polymers containing large soluble diethynyl iptycenes.
Organic letters,vol.7,p.4357–60,2005[structures: see text] An efficient synthesis of large iptycenes appended with alkoxy and ethynyl substituents is reported. The rigid shape-persistent iptycene scaffold prevents interactions between the polymer backbones and can be used to solubilize polymers containing less soluble but readily accessible comonomers to prepare functional, solution-processible poly(p-phenyleneethynylene) (PPE)-conjugated polymers. These polymers are highly emissive in thin films without significant excimer/exciplex formation as a result of the effective chain isolation enforced by the iptycene units. -
2005
A block copolymer nanotemplate for mechanically tunable polarized emission from a conjugated polymer
Polymer,vol.46,p.10113–10118,2005A polymer blend system consisting of polystyrene grafted onto poly(p-phenylene ethynylene) (PS-g-PPE) and poly(styrene-block-isoprene-block-styrene) triblock copolymer (SIS) yields highly polarized emission due to the unidirectional alignment of the PPE mols. During the roll casting, the triblock copolymer microphase separates and creates unidirectionally aligned PS cylindrical microdomains in the rubbery PI matrix. PPE, a fluorescent conjugated polymer, was grafted with polystyrene (PS) side chains that enabled sequestration and alignment of these rigid backbone emitter mols. into the PS microdomains of the SIS triblock copolymer. Deforming the thermoplastic elastomer in a direction perpendicular to the orientation direction of the cylinders causes rotation of the PS cylinders and the PPE emitter mols. and affords tunable polarized emission due to reorientation of the PPE contg. PS cylinders as well as film thinning from Poisson effect. [on SciFinder(R)] -
2004
Effect of Phase Retardation on Defect-Mode Lasing in Polymeric Cholesteric Liquid Crystals
Advanced Materials,vol.16,p.779–783,2004The authors studied the effects of an anisotropic nematic liq, crystal (NLC) defect layer introduced between polymeric cholesteric liq. crystals (PCLC) layers. It was found that the modulation of reflectance exceeds the 50 % limitation provided by simple CLC photonic bandgap (PBGs) due to the birefringence of the defect layer. Moreover, by adjusting the PBG region to be coincident with the fluorescent emission band for the guest polymer dye, sharp defect-mode lasing was obsd. successfully at the defect mode in the middle of PBG. From these results, it was demonstrated that the configuration of a PCLC with a polymer-dye-doped anisotropic defect layer is very attractive for lasing. [on SciFinder(R)] -
2004
Charge-specific interactions in segmented conducting polymers: an approach to selective ionoresistive responses.
Angewandte Chemie, International Edition,vol.43,p.3700–3703,2004 -
2004
Biotinylated poly(p-phenylene ethynylene): unexpected energy transfer results in the detection of biological analytes.
Chemical Communications,p.2798–9,2004Decreased spectral overlap between a donor biotinylated poly(p-phenylene ethynylene) and a chromophore-labeled streptavidin acceptor leads to better observed fluorescence resonance energy transfer. -
2004
Enhanced fluorescence quenching in receptor-containing conjugated polymers: a calix[4]arene-containing poly(phenylene ethynylene).
Chemical Communications,p.2744–5,2004A fluorescent poly(phenylene ethynylene) containing calix[4]arene-based receptor units has a sensitivity to quenching by the N-methylquinolinium ion that is over three times larger than that seen in a control polymer lacking calix[4]arenes. -
2004
Orientational ordering of short LC rods in an anisotropic liquid crystalline polymer glass.
Chemical Physics Letters,vol.389,p.198–203,2004The orientational phase diagram and ordering of guest liq. cryst. (LC) rods in a host liq. cryst. polymer (LCP) matrix quenched below the glass transition is detd. by field theory. Microscopic anisotropic interactions can align the LC rods to each other and also align LCP matrix side chains and the LC rods in the plane normal to the local LCP chain contour. The authors’ numerical anal. suggest ways to exploit host entropy, anisotropy of microscopic interactions and manipulate properties of LC rods for modern applications. The authors predict a nematic-nematic discontinuous orientational transition from a guest stabilized to a guest-host stabilized region and a reentrant transition from a guest stabilized nematic region to a host only stabilized regime. A detailed anal. of phase boundaries transitions and ordering is presented. [on SciFinder(R)] -
2004
Molecular Actuators—Designing Actuating Materials at the Molecular Level
IEEE Journal of Oceanic Engineering,vol.29,p.692–695,2004 -
2004
Advantages of Highly Ordered Polymer-Dyes for Lasing in Chiral Nematic Liquid Crystals
Japanese Journal of Applied Physics,vol.43,p.631–636,2004Lasing in dye-doped chiral nematic liq. crystals (N*LCs) was studied. To demonstrate the advantages of using a polymer dye, that is highly aligned along the local director of N*LCs, over com. small mol. dyes such as 4-(dicyanomethylene)-2-Me-6-(4-dimethylaminostryl)-4H-pyran (DCM), comparative studies of the fluorescence, lasing conditions and order parameters were made using polymer-dye doped N*LC and DCM-doped N*LC cells. Right- and polarized fluorescence spectra for both dyes were accurately simulated by taking account of their d. of modes and order parameters. The greater alignment afforded by the polymer dye in N*LCs provides ideal conditions for lasing. [on SciFinder(R)] -
2004
Detection of bacteria with carbohydrate-functionalized fluorescent polymers.
Journal of the American Chemical Society,vol.126,p.13343–6,2004Many pathogens that infect humans use cell surface carbohydrates as receptors to facilitate cell-cell adhesion. The hallmark of these interactions is their multivalency, or the simultaneous occurrence of multiple interactions. We have used a carbohydrate-functionalized fluorescent polymer, which displays many carbohydrate ligands on a single polymer chain, to allow for multivalent detection of pathogens. Incubation of a mannose-functionalized polymer with Escherichia coli yields brightly fluorescent aggregates of bacteria. These results show that carbohydrate-functionalized fluorescent polymers are a versatile detection method for bacteria. Future design of detectors for other pathogens only requires information on the carbohydrates bound by the organisms, which has been exhaustively reported in the literature. -
2004
Dynamic nuclear polarization with biradicals.
Journal of the American Chemical Society,vol.126,p.10844–5,2004Dynamic nuclear polarization (DNP) experiments in rotating solids have been performed for the first time using biradicals rather than monomeric paramagnetic centers as polarizing agents. Specifically, two TEMPO radicals were tethered with a poly(ethylene glycol) chain of variable length where the number of glycol units was 2, 3, or 4. NMR experiments show that the signal observed in DNP experiments is approximately inversely proportional to the length of the chain. Thus, the shorter chain with larger electron dipolar couplings yields larger enhancements. The size of the enhancement is a factor of 4 larger than obtained with the identical concentration of monomeric nitroxide radicals achieving a value of approximately 175 for the n = 2 chain. -
2004
Rotaxanated Conjugated Sensory Polymers.
Journal of the American Chemical Society,vol.126,p.8638–8639,2004The prepn. of two highly emissive conjugated polyacetylenes with tethered rotaxane repeat units are reported. Hydrogen bonding between acidic alcs. and the N-heteroarom. groups in the rotaxanes attenuates polymer fluorescence. In addn., the rotaxane groups create precise three-dimensional pockets for metal binding, which results in fluorescence quenching. Exposing thin films of Zn-doped polymers to alc. vapors reverses the quenching by up to 25%. [on SciFinder(R)] -
2004
Hyperconjugative and inductive perturbations in poly(p-phenylene vinylenes).
Journal of the American Chemical Society,vol.126,p.452–3,2004New polymers having high solid-state fluorescence quantum yields and the ability to tune their electron affinity without effecting their band gap using hyperconjugative interactions is reported. The novel three-dimensional poly(phenylene vinylenes) having [2.2.2] bicyclic ring systems shown were synthesized, and the different hyperconjugative perturbations provide differential fluorescence sensory quenching responses to electron-rich and electron-deficient analytes in solution and solid thin films. -
2004
Incorporation of Internal Free Volume: Synthesis and Characterization of Iptycene-Elaborated Poly(butadiene)s
Macromolecules,vol.37,p.3068–3070,2004Prepn. and characterization of 3 high mol. wt. iptycene-contg. polybutadienes as well as their starting monomers (derived from anthracene, tetracene, and 1,4-anthraquinone via initial Diels-Alder reactions followed by operations such as hydrogenation, dehydrohalogenation, and dehydration) are described. All monomers at least possessed a butadiene unit that was used for radical polymn. leading to polymers presenting an internal free vol. that could be utilized for the enhancement of miscibility and redn. of phase sepn. in polymer blends. [on SciFinder(R)] -
2004
Fluorescent Semiconducting Polymer Conjugates of Poly( N -isopropylacrylamide) for Thermal Precipitation Assays
Macromolecules,vol.37,p.716–724,2004New thermally responsive fluorescent polymers conjugated with poly(N-isopropylacrylamide) (polyNIPA) were synthesized. A nonionic water-sol. poly(phenyleneethynylene) (PPE) was end-capped with a di-tert-butylnitroxide deriv., and subsequent nitroxide-mediated radical polymn. of NIPA afforded PPE-polyNIPA block copolymers. These copolymers phase-sep. from aq. solns. upon heating, and the resultant ppts. are efficiently collected by filtration. The fluorescent spectra of the ppts. indicate the absence of strong assocns. between the PPE $π$-systems. Furthermore, the fluorescent intensities of the collected solids have a linear correlation with the polymer concns. in the solns. of origin. When copolymers are thermally copptd. with dye-labeled (rhodamine B) polyNIPA materials, the dye is localized to the PPE segments, inducing fluorescent resonance energy transfer from the PPE segment (donor) to the dye (acceptor). [on SciFinder(R)] -
2004
Synthesis and Characterization of Triphenylene-Dione Half-Disc Mesogens
Molecular Crystals and Liquid Crystals,vol.411,p.363–375,2004Novel half-disk mesogens of general structure 6,7,10,11-tetrakis(alkoxy)triphenylene-1,4-dione were synthesized and their phases characterized by polarized microscopy, DSC and x-ray diffraction. These compds. form hexagonal columnar mesophases upon heating, despite their half-disk mol. shapes. X-ray diffraction suggests that within the mesophases a dimeric mesogenic subunit exists, driven by dipolar forces, in which the mols. are oriented antiparallel to one another. Such a dimer is approx. disk-shaped, and may explain the formation of columnar phases by these half-disk mols. [on SciFinder(R)] -
2004
Chiral Supramolecular Materials from Columnar Liquid Crystals
Molecular Crystals and Liquid Crystals,vol.410,p.247–253,2004Several $\beta$-diketonate ligands were synthesized which have a chiral directing element and/or a polymerizable moiety. Octahedral iron complexes of these ligands were crosslinked in the columnar hexagonal phase using acyclic diene metathesis (ADMET) polymn. The resulting liq. crystal materials were chiral and retained the order of the mesophase. [on SciFinder(R)] -
2004
Polymer electronics for explosives detection.
NATO Science Series, II: Mathematics, Physics and Chemistry,vol.159,p.29–37,2004A review of the amplifying ability of semiconductive org. polymers in sensory schemes and its use for the detection of nitroarom. explosives. Semiconductive org. polymers serve as extremely efficient conduits for the transport of optically induced excitations and it is this transport property that allows for the high sensitivity of these materials to trinitrotoluene (TNT) and dinitrotoluene (DNT), the primary explosives used in landmines. Systematic mol. designs for the formation of improved sensitivity sensory materials are described. [on SciFinder(R)]
