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2006
Tunable columnar mesophases utilizing C2 symmetric aromatic donor-acceptor complexes.
Journal of the American Chemical Society,vol.128,p.7995–8002,2006Derivatives of relatively electron rich 1,5-dialkoxynaphthalene (Dan) donors and relatively electron deficient 1,4,5,8-naphthalenetetracarboxylic diimide (Ndi) acceptors have been exploited in the folding and self-assembly of a variety of complex molecular systems in solution. Here, we report the use of Dan and Ndi derivatives to direct assembly of extended columns with alternating face-centered stacked structure in the solid state. A variety of 1:1 Dan:Ndi mixtures produced mesophases that were found to be stable over temperature ranges extending up to 110 degrees C. Analysis of these mesophases indicates mixtures with soft/plastic crystal phases and a few mixtures with the thermodynamic properties of true liquid crystals, all composed of alternating donor-acceptor columns within. Importantly, a correspondence was found between the clearing and crystallization points of the mesophase mixtures and the melting/clearing points of the component Ndi and Dan units, respectively. This correspondence enables the predictable tuning of mesophase phase transition temperatures. The study of sterically hindered derivatives led to a set of mixtures in which a dramatic and sudden color change (deep red to yellow) was observed upon crystallization of the mesophase due to a phase separation of the component donor and acceptor units. -
2006A series of 2,5-thiophene-substituted 1′,2′,3′,4′,5′-pentamethylazaferrocene complexes were synthesized and electropolymerized to produce polymers with fully pi-conjugated backbones. The length and hence oxidation potential of the conjugated linker (the thiophene fragments) between the metal centers were varied to understand the influence of the metal-metal interactions on the overall electroactivity of the resulting polymer. These complexes were electrochemically polymerized, and the resulting polymers were characterized by cyclic voltammetry, in situ conductivity, and spectroelectrochemistry measurements. The iron-centered oxidations significantly increased the conductivity of the polymer. The results reveal that shorter conjugated linkers cause the onset of conductivity to occur at lower potentials. This effect implies that a superexchange mechanism is likely operative in the charge migration of these polymers.
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2006
Anthryl-Based Poly(phenylene ethynylene)s: Tuning Optical Properties with Diels−Alder Reactions
Macromolecules,vol.39,p.7854–7858,2006Sol. anthryl-based conjugated poly(phenylene ethynylene)s (PPEs) have been synthesized using palladium-catalyzed Sonogashira-Hagihara cross-coupling polymn. reactions. Mol. wts. up to 3.5 × 104 g•mol-1 were obtained, making them suitable for spectroscopic soln. characterizations and thin film processing. The selective reactivity of these polymers as multidienes has been successfully demonstrated with strong dienophiles. Diels-Alder reactions proceed cleanly to completion with unhindered dienophiles such as N-alkylated maleimide derivs. TGA anal. revealed thermal retro-Diels-Alder reactions at modest temps. around 210 °C. Compared with their parent polymers, the cycloadduct polymers exhibited dramatic hypsochromic shifts of their emission and absorption maxima up to 80 nm along with a considerable quantum yield enhancement. These original anthryl-based polymers appear attractive as reactive conjugated materials whose optical properties can easily be tuned with quant. Diels-Alder reactions. [on SciFinder(R)] -
2006
Highly Effective Water-Soluble Fluorescence Quenchers of Conjugated Polymer Thin Films in Aqueous Environments
Macromolecules,vol.39,p.7175–7177,2006This paper reports water-sol. viologen quenchers that bear hydrophobic substituents and describes their effectiveness as quenchers of emission from thin films of hydrophobic, water-insol. poly(p-phenylene ethynylene)s. [on SciFinder(R)] -
2006
Probing Biological Recognition Using Conjugated Polymers at the Air−Water Interface
Macromolecules,vol.39,p.6781–6783,2006The effect of linker length on biol. recognition at the air-water interface using energy transfer between a fluorescent conjugated polymer and dye-labeled protein. A longer linker provided greater binding of the protein as evidence by the dramatically increased energy transfer. This may be due to an increased hydrophilicity of the side chain, which allowed the biotin to better access the streptavidin located in the aq. subphase. Subtle changes in the polymer structure can thus have important consequences for analyte recognition. [on SciFinder(R)] -
2006Tropone-Contg. thiophene monomers were prepd. and electrochem. polymd. under ambient conditions to form polymers. The polymers with various concns. of TFA were studied by CV, UV-vis-NIR, and cond. In conclusion, the cond. of tropone-contg. polythiophene can be switched reversibly by a protonation/deprotonation process. The cond. switching mechanism of this polymer is alternative to that of conventional proton dopable polymers such as polyaniline. [on SciFinder(R)]
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2006
Conjugated Polymers with Geminal Trifluoromethyl Substituents Derived from Hexafluoroacetone
Macromolecules,vol.39,p.5753–5759,2006Convenient syntheses of 9,9-bis(trifluoromethyl)fluorene and 6,6,12,12-tetrakis(trifluoromethyl)indenofluorene are reported. The monomers were readily prepd. in two steps from simple halo-aroms. and hexafluoroacetone, which serves as the source of the geminal trifluoromethyl groups. Iodination yields polymerizable monomers that were used to prep. several conjugated polymers. The photophys. properties of these polymers are reported. The polymers demonstrate slightly blue-shifted UV-vis absorption and fluorescence emission spectra and high soln. and solid-state fluorescence quantum efficiency. Polymer photobleaching expts. reveal that poly(fluorene)s with geminal trifluoromethyl substituents demonstrate greater photooxidative stability than poly(9,9-dioctylfluorene). [on SciFinder(R)] -
2006
Sensory Polymers for Electron-Rich Analytes of Biological Interest
Macromolecules,vol.39,p.5177–5179,2006A report on a water-sol. photooxidizing amplifying fluorescent polymer (AFP) and its performance in photoinduced electron transfer (PET) based detection of amino acids, neurotransmitters, and proteins possessing electron-donating arom. moieties in aq. buffer is presented. This report has shown that a water-sol. photooxidizing AFP could serve as a PET-based sensor for amino acids, neurotransmitters and proteins with electron-donating arom. compds. in aq. media. The results show that the quenching efficiency is strongly dependent on electrostatic interaction of the anionic polymer and quencher as well as hydrophobic and electron-transfer interactions between the polymer chains and quencher. [on SciFinder(R)] -
2006
Synthesis and Characterization of Poly(isobenzofuran) Films by Chemical Vapor Deposition
Macromolecules,vol.39,p.4400–4410,2006This paper describes the synthesis and properties of poly(isobenzofuran) (PIBF) films prepd. by a thermal chem. vapor deposition (CVD) process. The synthesized precursor monomer, 1,2,3,4-tetrahydro-1,4-epoxynaphthalene, is pyrolyzed by flowing it through a tube furnace at temps. of 600-750°. A reactive intermediate, isobenzofuran (IBF) monomer, is produced by this pyrolysis and deposited onto a silicon substrate where it polymerizes to form a thin coating of poly(isobenzofuran) (PIBF) on the surface. The chem. structure and compn. of the PIBF films are supported by NMR spectroscopy, Fourier transform IR spectroscopy (FT-IR), and XPS. The wt.-av. mol. wt. of the PIBF films range from 5500 to 9400 by varying the deposition (stage), pyrolysis (furnace), and vaporization (source) temps. With the variation of deposition temp. (5, 10, 15, 20, 25°) and pyrolysis temp. (600, 650, 700, 750°), significant changes are obsd. in deposition (growth) rate, mol. wt., and morphol. while the chem. structure of the PIBF films remain the same as probed by FT-IR and XPS anal. On the other hand, variation of the vaporization temp. (40, 45, 50, 55, 60°) leads to significant changes in the chem. structure as well as in the deposition rate, mol. wt., film uniformity, and morphol. By exploring several operating conditions, we have obtained optimal conditions for deposition temp. (10°), pyrolysis temp. (750°), and vaporization temp. (60°) that provide good film properties as well as fast film growth. To investigate the possible role of cationic initiation in IBF polymn., PIBF films were deposited on several surfaces tailored with self-assembled monolayers (SAMs) of thiols that have functional groups of different acidities, including a carboxylic acid (-COOH), a phenol (-PhOH), an alc. (-OH), an amine (-NH2), and a Me group (-CH3). We obsd. the fastest growth of PIBF (k = 2.5 AA/s) on the carboxylic acid-terminated surfaces whereas the slowest growth was on the methyl-terminated surfaces (k = 0.02 AA/s). On the basis of the exptl. observations, we proposed a growth mechanism for the PIBF films by the CVD process. [on SciFinder(R)] -
2006A self-polymerizable AB-type monomer for Diels-Alder (D-A) polymn. was prepd., and its polymn. was carried out in the melt phase and at high pressure in soln. The former method generated only low-mol.-wt. polymer, but the latter one offered an efficient polymn. with increased mol. wt., due to the effect of high pressure on reactions with a neg. activation vol. A pyridinium p-toluenesulfonate-catalyzed dehydration reaction of the D-A polymer led to a novel arom. ladder polymer, poly(iptycene), which is sol. in common org. solvents and stable up to 350 °C. The NMR and UV-vis spectra of these polymers match the spectra of their corresponding model compds., the synthesis of which is also reported. [on SciFinder(R)]
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2006
Minimization of Internal Molecular Free Volume: A Mechanism for the Simultaneous Enhancement of Polymer Stiffness, Strength, and Ductility
Macromolecules,vol.39,p.3350–3358,2006The prepn. and mech./structural characteristics were studied of a polyester contg. 21% triptycene monomer, vs. a ref. polyester homolog wherein benzene replaces the triptycene residue. Solvent-cast films and tension heat-treated (THT) films were studied by tensile deformation and wide-angle x-ray scattering. The addn. of triptycene units increases the Tg and, contrary to what is typically obsd., also increases the ductility of film samples. In comparison to the solvent-cast non-triptycene polyester films, the triptycene polyester films displayed a nearly 3-fold increase in Young’s modulus, an approx. 3-fold increase in strength, and a more than 20-fold increase in strain to failure. THT films of the triptycene polyester exhibited a modulus more than 7 times that of the non-triptycene as-cast polyester and strength greater than 14 times higher for roughly the same strain to failure. This unusually beneficial mech. behavior is primarily attributed to the ability of individual triptycene units to express what was termed as internal mol. free vol. (IMFV). The triptycene polymers adopt favorable conformations that minimize the IMFV, and the resultant assembly introduces two mechanisms for the enhancement of tensile mech. properties: mol. threading and mol. interlocking. [on SciFinder(R)] -
2006
Masked Michael Acceptors in Poly(phenyleneethynylene)s for Facile Conjugation
Macromolecules,vol.39,p.2815–2818,2006Poly(phenyleneethynylene)s (PPEs) capable of reacting with thiol-contg. mols. have been designed and synthesized with no.-av. mol. wts. ranging from 8000 to 11,000. The PPEs contain pendent 3a,4,7,7a-tetrahydro-4,7-epoxy-1H-isoindole-1,3(2H)-dione groups available to participate in conjugate addn. and Diels-Alder chem. after being thermally activated. If the maleimide group is left unmasked during palladium-catalyzed cross-coupling polymn., it leads to side reactions and the prodn. only of short chain oligomers (Mn < 3000, DP ∼ 4). Reversible Diels-Alder reactions between the maleimides and furan were detd. to be a very effective method to produce a masked Michael acceptor that can be unveiled after polymn. under relatively mild thermal conditions. Cycloreversion to the maleimide has been monitored by thermogravimetric anal. (TGA), TGA-MS, IR, and NMR. A PPE contg. the masked maleimide unit has been modified with a thiolated carboxy-X-rhodamine (ROX) dye, and the resulting absorbance and fluorescence spectra as well as gel permeation chromatograms (GPC) are presented. [on SciFinder(R)] -
2006
Main-Chain Calixarene Polymers: Conformational Effects on Polymerization
Macromolecules,vol.39,p.2013–2015,2006We have synthesized high-mol.-wt. main-chain calixarene homopolymers via linkages on lower rims. We have found that the calixarene conformation has a profound influence on the polymn. Our synthetic methodol. can be applied to the polymns. of other sterically demanding and conformationally flexible monomers. Main-chain calixarene polymers linked through the lower rims present new opportunities to create efficient sepns., and materials for sensing and actuation, as a result of their dynamic receptor properties. [on SciFinder(R)] -
2006[reaction: see text] The syntheses of a series of fluorine- and alkyl/alkoxy-functionalized tetracenes are reported. These functional groups are found to improve the solubility in common organic solvents and tune molecular arrangement in solids. The crystal packing, electrochemical behavior, and UV-vis absorbance spectroscopy of these materials are discussed.
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2006
Polymerization of thiophene containing cyclobutadiene Co cyclopentadiene complexes
Synthetic Metals,vol.156,p.784–791,2006To understand the charge transport ability of metal coordinated cyclobutadiene, a series of cyclobutadiene cobalt cyclopentadiene (CbCoCp) complexes contg. electrochem. polymerizable 3,4-ethylenedioxythiophene units were synthesized. The complexes were electrochem. polymd. and the resulting polythiophenes were characterized by cyclic voltammetry, in situ cond. and UV-vis spectroelectrochem. Several different derivs. of the CbCoCp complexes and a model study suggested that if the oxidn. of the org. fragment was above CoI/II redox couple of the CbCoCp complex, detrimental side reactions occurred. Side reactions did not occur if the oxidn. potential of the org. fragment was below the oxidn. potential of the metal. [on SciFinder(R)] -
2005
Highly Efficient Blue Electroluminescence from Poly(phenylene ethynylene) via Energy Transfer from a Hole-Transport Matrix
Advanced Materials,vol.17,p.1981–1985,2005Blue poly(phenylene ethynylene) (PPE) electroluminescence (EL, see Figure) is obsd. in a hybrid org. light-emitting diode (OLED) with Commission Internationale de l’Eclairage coordinates of (x = 0.17; y = 0.20). Energy transfer from a hole-transport host to polystyrene-grafted PPEs is utilized to improve the poor LED characteristics of traditional PPE-based systems. [on SciFinder(R)] -
2005
Poly(arylene ethynylene)s in chemosensing and biosensing.
Advances in Polymer Science,vol.177,p.151–179,2005A review. Poly(arylene ethynylene)s (PArEs) have been used in recent years as effective transducers for a variety of sensing purposes ranging from org. mols. such as Me viologen and TNT to biol. analytes. Their superior sensitivity to minor perturbations is fundamentally governed by the energy transport properties resulting from the extended conjugation of the polymer backbone. An understanding of the underlying principles of energy transport allows the design of sensors with greater sensitivity and specificity. Pioneering work with Me viologen as an electron-transfer quencher demonstrated that connecting receptors in series amplifies the sensing response compared to that of individual receptors. Since then, factors such as the electronic and structural nature of the polymers and their assembly architecture have proven to be important in improving sensory response. In this review, the authors present an overview of works to date by various groups in the field of PArE chemosensors and biosensors. [on SciFinder(R)] -
2005
In vivo optical imaging of amyloid aggregates in brain: design of fluorescent markers.
Angewandte Chemie, International Edition,vol.44,p.5452–6,2005Routine diagnostics and studies of Alzheimer’s disease might benefit form the noninvasive optical imaging of amyloid-$beta$ plaques in the brain. A rational design strategy for in vivo amyloid-imaging agents that enter the brain and selectively stain amyloid plaques is presented (see picture), and properties of a promising lead biomarker candidate are reported. [on SciFinder(R)] -
2005
One-Dimensional Metals. Conjugated Polymers, Organic Crystals, Carbon Nanotubes. By Sigmar Roth and David Carroll.
Angewandte Chemie, International Edition,vol.44,p.2473–2473,2005 -
2005Poly(p-phenylenevinylene)s containing trifluoromethyl substituted aromatic rings (CF3-PPVs) exhibit high photooxidative stability to give robust materials suitable for demanding applications.
