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2001
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2001
Conducting Polymers Incorporating Tungsten-Capped Calixarenes
Journal of the American Chemical Society,vol.123,p.7917–7918,2001 -
2001
Mass and Energy Transport in Conjugated Polymer Langmuir-Blodgett Films: Conductivity, Fluorescence, and UV-Vis Studies.
Macromolecules,vol.34,p.2315–2319,2001We have investigated a model thin film sensory system in which analytes diffuse into multilayers of a fluorescent conjugated polymer. The film thickness is precisely controlled by depositing discrete monolayers by the Langmuir-Blodgett technique. The effects of analyte mass transport and energy migration on the photophys. properties of the films were investigated by conducting UV-vis, fluorescence, and elec. cond. measurements. Thin films show different properties when compared to relatively thick films due to prevailing surface phenomena. The diffusion const. of the analyte through the films is estd. to be ∼7 × 10-14 cm2/s from an anal. of a phenomenol. model. A bilayer LB film exposed to the analyte implies higher sensitivity in fluorescence quenching compared to a soln. system due to a fast interpolymer energy migration in the condensed phase. However, as the no. of layers increases, the efficiency of fluorescence quenching decreases. The difference between a sensory system with emissive surface traps and one with bulk distributed quenching traps is discussed. [on SciFinder(R)] -
2001
Regiospecific Copolyanilines from Substituted Oligoanilines: Electrochemical Comparisons with Random Copolyanilines
Macromolecules,vol.34,p.812–816,2001Regiospecific substituted polyanilines were prepd. via electropolymn. of methoxy-substituted dimeric and trimeric oligoanilines. The oligoaniline monomers were synthesized utilizing Pd-catalyzed aryl amination cross-coupling chem. The single-crystal x-ray structure of one of the oligomers is presented. The oligoaniline monomers were electropolymd. in 1 M H2SO4, and the electrochem. behavior and potential-dependent in situ cond. of the regiospecific polyaniline films was compared to that of random copolymers obtained from solns. of aniline and o-anisidine of the same molar ratio. The regiospecific polyanilines exhibited higher cond., which may be attributed to a more cryst. and regular structure. Differences in the oxidn. potential of the polymers are obsd. depending on the degree of methoxy substitution. [on SciFinder(R)] -
2001
Control of conformational and interpolymer effects in conjugated polymers.
Nature,vol.411,p.1030–4,2001The role of conjugated polymers in emerging electronic, sensor and display technologies is rapidly expanding. In spite of extensive investigations, the intrinsic spectroscopic properties of conjugated polymers in precise conformational and spatial arrangements have remained elusive. The difficulties of obtaining such information are endemic to polymers, which often resist assembly into single crystals or organized structures owing to entropic and polydispersity considerations. Here we show that the conformation of individual polymers and interpolymer interactions in conjugated polymers can be controlled through the use of designed surfactant poly(p-phenylene-ethynylene) Langmuir films. We show that by mechanically inducing reversible conformational changes of these Langmuir monolayers, we can obtain the precise interrelationship of the intrinsic optical properties of a conjugated polymer and a single chain’s conformation and/or interpolymer interactions. This method for controlling the structure of conjugated polymers and establishing their intrinsic spectroscopic properties should permit a more comprehensive understanding of fluorescent conjugated materials. -
2001
Conjugated Polymers Containing 2,3-Dialkoxybenzene and Iptycene Building Blocks
Organic Letters,vol.3,p.3471–3474,2001[structure: see text]. New poly(phenylene ethynylene)s (PPEs) and poly(phenylene vinylene)s (PPVs) that are highly emissive in solution and thin films were prepared utilizing palladium-catalyzed cross-coupling between new 1,4-diiodo-2,3-dialkoxybenzene- and iptycene-containing monomers. The absorption and emission spectra of the resulting polymers consistently showed a significant blue shift relative to the corresponding polymer analogues containing 2,5-dialkoxyphenylenes.[on SciFinder (R)] -
2001
Polymers containing iptycenes.
Polymeric Materials Science and Engineering,vol.84,p.304–305,2001Recent research on producing polyiptycenes (polymers contg. triptycene units in the backbone) is discussed. The highly rigid structure of these polymers provides large degrees of free vol. and a host of novel properties. [on SciFinder(R)] -
2000
Ion-Specific Aggregation in Conjugated Polymers: Highly Sensitive and Selective Fluorescent Ion Chemosensors
Angewandte Chemie, International Edition,vol.39,p.3868–3872,2000A new transduction mechanism based on the aggregation of conjugated sensory polymers induced by K+ ions is reported; this new system displays enhanced sensitivity because of energy migration processes and has a high selectivity for K+ over Na+ ions. The poly(p-phenylene ethynylene)s were synthesized by the Sonogashira-Hagihara coupling reaction. [on SciFinder(R)] -
2000
A highly conductive macrocycle-linked metallophthalocyanine polymer.
Angewandte Chemie, International Edition,vol.39,p.2897–2900,2000A highly electroactive polythiophene-metallophthalocyanine hybrid material was prepd. which exhibits cond. more than three orders of magnitude higher than that of know macrocycle-connected polymers. The triptycene-contg. phthalocyanine macrocycle monomers have electrochem. polymerizable thiophene moieties on alternating subunits which give nearly linear polymer backbone with the metal center in direct electronic communication with the conjugated polymer backbone. The electrochem. polymn. proceeds through oxidative coupling of pendant thiophenes. The cyclic voltammogram of the Ni complex polymer displays prominent features in the reductive region at -1.35 and -1.75 V assignable to the Ni redox and ligand-centered processes, resp. The polymer shows both metal-centered electroactivity and high cond. and the Ni redox wave does not contribute to the cond. [on SciFinder(R)] -
2000
Three-strand conducting ladder polymers: two-step electropolymerization of metallorotaxanes.
Angewandte Chemie, International Edition,vol.39,p.608–612,2000Rotaxane recognition and assembly methods were used to produce new architectures based on a metallorotaxane (Cu, Zn) monomer bearing two independently electropolymerizable groups in the threading unit and the macrocycle host. The controlled assembly and polymn. of the metallorotaxane monomers leads to three-stranded ladder polymers, wherein one of the conjugated chains is sandwiched between two other chains. In this structure the internal polymer behaves as a partially isolated mol. wire when the outer strands are in an insulating state. Neglecting minor effects arising from conformational issues (there are two enantiomeric conformations) the polymer formed from the threading unit is twice as long as the polymer contg. the macrocycle. When the outer polymer chains are insulating, the electroactivity of Cu or Zn ions can assist in interchain transport. [on SciFinder(R)] -
2000A review with 359 refs. is given on conjugated polymers with synthetic receptors and functional groups, biol. sensors, conjugated polymers with entrapped materials to aid in specificity, and unmodified conjugated polymers as sensors. [on SciFinder(R)]
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2000
Electrocatalytic Conducting Polymers: Oxygen Reduction by a Polythiophene-Cobalt Salen Hybrid.
Chemistry of Materials,vol.12,p.872–874,2000Highly conducting polythiophene-cobalt salen hybrid material catalyzed the redn. of O2. Rotating ring-disk measurements suggested a selective four-electron redn. process took place to produce H2O as the sole product. [on SciFinder(R)] -
2000
Molecular photonic and electronic circuitry for ultra-sensitive chemical sensors
Current opinion in chemical biology,vol.4,p.715–720,2000Molecular wires have progressed from an intellectual curiosity to become the basis for chemical sensors with unprecedented sensitivity. Particularly exciting opportunities are those that make use of biological superstructures to effect conduction through assemblies of molecular wires.[on SciFinder (R)] -
2000
An improved synthesis of poly(p-phenylenebutadiynylene)s.
Journal of Polymer Science, Part A: Polymer Chemistry,vol.38,p.4669–4676,2000A new methodol. is described for the synthesis of poly(p-phenylenebutadiynylene)s based on the Pd/Cu-catalyzed, benzoquinone-mediated homocoupling of terminal acetylenes. Homopolymers synthesized from the 2,5-dialkoxy-1,4-diethynylbenzene monomers 1,4-bis(decyloxy)-2,5-diethynylbenzene and 1,4-bis(hexadecyloxy)-2,5-diethynylbenzene were largely insol., with the sol. portion from the polymn. of 1,4-bis(hexadecyloxy)-2,5-diethynylbenzene exhibiting a no.-av. mol. wt. of 14,000. Completely sol. polymers were obtained from these precursors by the random copolymn. of these monomers. The materials exhibited no.-av. mol. wts. ranging from 67,000 to over 150,000. The UV-visible and emission spectra of these polymers were examd. and found to be very similar to those of structurally analogous poly(p-phenyleneethynylene)s and smaller poly(p-phenylenebutadiynylene)s reported by Kijima et al. [on SciFinder(R)] -
2000
Signal Amplification of a \”Turn-On\” Sensor: Harvesting the Light Captured by a Conjugated Polymer.
Journal of the American Chemical Society,vol.122,p.12389–12390,2000A chemosensor design is presented which substantially amplifies the output of a pH-sensitive fluorophore using energy harvested from a conjugated polymer. The construction of thin films was accomplished via layer-by-layer deposition of a new water-sol., cationic poly(p-phenylene ethynylene) (PPE) and an anionic polyacrylate. [on SciFinder(R)] -
2000
A Conducting Poly(cyclophane) and Its Poly([2]-catenane).
Journal of the American Chemical Society,vol.122,p.9300–9301,2000Cyclization of 1,4-Bis[2-(2-(2-(2-toluene-p-sulfonylethoxy) ethoxy) ethoxy) ethoxy]benzene with 1,4-diiodo-2,5-dihydroxybenzene, followed by coupling with (3,4-ethylenedioxy)-thiophene produced 1,4-Bis((3,4-ethylenedioxy)thiophene)-7,10,13,16,19,26,29,32,35,38-decaoxa[13.13]paracyclophane (I) a highly fluorescent electropolymerizable monomer and electron donor. Addn. of Paraquat to I in CH3CN resulted in formation of a deep-green colored soln. with a charge-transfer absorption band at $łambda$ = 589 nm ($ε$ = 204 M-1cm-1), indicative of the highly electron-donating nature of the thiophene-phenylene-thiophene arom. scaffold. The tetrakis-hexafluorophosphate I-[2]-catenane complex (II) was prepd. by reaction of I with NH4PF6 and 1,4-bis(bromomethyl)benzene. The deep-green complex II exhibits a charge-transfer absorption at $łambda$ = 626 nm ($ε$ = 1230 M-1 cm-1), which is red-shifted relative to that of Paraquat:I complex indicating greater intimacy between donor and acceptor in the [2]-catenane. The crystal structure of II indicates an interlocked $π$-stacked geometry with inner bipyridinium moieties within the cyclophane cavity and outer bipyridinium on the periphery of the cavity. Electrochem. polymn. of I and II proceeds via two propagating sites at the 5-position of 3,4-ethylenedioxythiophene and affords conducting polymers. Oxidn. and redn. potentials for poly-II are identical to those of II monomer suggesting that the neutral polymer backbone has the same electronic influence as the thiophene-phenylene-thiophene in II. For both poly-I and poly-II, the multiple redn. peaks obsd. are indicative of the energetic inequality between the inner- and outer-bipyridinium groups. The cond. of poly-II rapidly reaches a max. of 0.2 S/cm at 0.12 V vs. Fc/Fc+, which decays quickly thereafter. In contrast, the cond. profile for poly-I shows that oxidn. of the backbone occurs over a broad range of potentials without decay. The absorption spectra of both conducting polymers are similar; in the neutral (insulating) form, the $łambda$max for poly-I was 527 nm (2.35 eV) and poly-II 542 nm (2.29 eV). When oxidatively doped, both displayed a longer wavelength band at 767-796 nm (1.62-1.56 eV), indicative of new states formed within the band gap upon reaching a conductive state. Further lower energy absorptions occur at higher oxidn. potentials leading to an absorption at >1100 nm (>1.13 eV) owing to the formation of free carriers. The films differ in that poly-II requires higher oxidn. potentials to reach its conductive state than does poly-I. [on SciFinder(R)] -
2000
A Poly(p-phenyleneethynylene) with a Highly Emissive Aggregated Phase.
Journal of the American Chemical Society,vol.122,p.8565–8566,2000A cyclophane-based poly(p-phenyleneethynylene) was prepd. and showed to undergo unusual solid-state aggregation to give highly emissive materials. This aggregation was demonstrated to be controllable via the method of film prepn. (Langmuir vs. spin-casting) with facile de-aggregation possible by the introduction of specific analytes or annealing. The subsequent decrease in the fluorescence intensities of spin-cast films after chem.-thermal modifications (due to chain alignment) has potential applications in sensor technologies. [on SciFinder(R)] -
2000
Two-Dimensional Conjugated Polymer Assemblies: Interchain Spacing for Control of Photophysics.
Journal of the American Chemical Society,vol.122,p.5885–5886,2000The relation between cofacial interpolymer distance and solid-state photophysics of random hydrophilic (Me, iso-Pr, isopentyl)- and hexadecyloxy hydrophobic-substituted poly(p-phenylene ethynylene)s was studied. The side chain bulk influences the packing of the polymers at the air-water interface, by providing greater polymer-polymer spacing. Interchain distance has a strong influence on the spectral properties of PPEs. Thin films were prepd. on glass substrates by drop casting, by spin casting, and by using the Langmuir-Schaefer (LS) method. Normalized UV-vis and PL spectra of the isopropyl-substituted PPV films spin cast, drop, and soln. are similar, illustrating the lack of order in the spin cast film relative to the LS film. However, the drop cast film has a PL max. at 463 nm arising from non-aggregated polymer chains, along with three other red-shifted peaks at 494, 512, and 553 nm which may arise from multiple aggregated states, indicating that the drop cast film is intermediate between the LS (fully aggregated case) and the spin cast (least aggregated state). [on SciFinder(R)] -
2000
Exciton coupling and dipolar correlations in a columnar liquid crystal: photophysics of a bent-rod hexacatenar mesogen.
Journal of the American Chemical Society,vol.122,p.2474–2479,2000A novel bent-rod hexacatenar liq. crystal is reported that displays a hexagonal columnar (Colh) phase. The organization of conjugated hexacatenar mesogens in the columnar phase is of interest for their anisotropic electronic properties. The emissive nature of the mesogens varies over the temp. range of the Colh phase and the spectral shifts were analyzed in terms of an exciton-coupling model. The variation of the emission band in this phase is consistent with varying degrees of rotational disorder between the mesogens. The bent-rod shape and highly dipolar nature of the liq. crystal core (mesogen) promotes (as suggested by computation, x-ray diffraction, and photophys. studies) a high degree of antiparallel intermol. correlations between nearest neighbors. The antiparallel organization is novel and differs from structures previously identified in other polycatenars. These studies illustrate the utility of the exciton-coupling model to probe the nature and degree of intermol. correlations in highly dipolar liq. crystals. [on SciFinder(R)] -
2000
Columnar phases of achiral vanadyl liquid crystalline complexes.
Liquid Crystals,vol.27,p.509–521,2000Two liq. cryst. vanadyl complexes were studied by frequency domain dielec. spectroscopy over the range 10 mHz to 13 MHz. The materials exhibit two or three columnar phases denoted Colro, Colrd, and Colhd that were identified by x-ray diffraction. In the higher temp. Colrd phase, a relaxation process in the kHz range is obsd. that is attributed to the reorientation about the mol. short axis. A pronounced dielec. relaxation process shows up in the low temp. Colro phase at hertz and sub-hertz frequencies. This slow relaxation is assigned to reorientation of the mol. dipoles within the polar linear chains, which are aligned along the column’s axis. Triangular wave switching studies at low frequency reveal processes inside the Colro phase which are most probably due to ionic/charges relaxations but a ferroelec. switching for an achiral discotic system cannot be ruled out completely. Below the Colro phase there is an orientationally disordered cryst. Crx phase with disordered side chain dipoles. A dielec. relaxation process connected with the intramol. relaxation of the alkoxy side chains, similar to the $beta$-process of polymers, was found in the lower temp. Crx phase. [on SciFinder(R)]
