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  • 1990-1994  (23)
  • 1980-1984  (11)
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  • 1
    Electronic Resource
    Electronic Resource
    A photoluminescence study of poly(phenylene vinylene) derivatives: The effect of intrinsic persistence length (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 101 (1994), S. 1673-1678 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We report the results of light scattering, absorption, excitation, and emission spectroscopy of three polyphenylene vinylene (PPV) derivatives; poly[2-methoxy, 5-(2'-ethyl-hexyloxy-p-phenylene- vinylene] (MEH-PPV), poly[2-butoxy, 5-(2'-ethyl-hexyloxy-p-phenylene-vinylene] (BEH-PPV), and poly[2-dicholestanoxy-p-phenylene-vinylene] (BCHA-PPV) in solution with p-xylene. We find that increasing the size of the solubilizing side chains increases the intrinsic persistence length of the polyphenylene vinylene backbone and that this change in stiffness has dramatic effects on the photoluminescence of polyphenylene vinylene. We have determined the luminescence quantum efficiencies of the polyphenylene vinylene derivatives relative to a known standard, Rhodamine 6G, and find that the photoluminescence can be greatly enhanced by increasing the intrinsic stiffness of the polymer backbone. The stiffest polymer, poly[2-dicholestanoxy-p-phenylene-vinylene] (BCHA-PPV), has a quantum efficiency of 0.66±0.05. The quantum efficiency decreases to 0.22±0.05 for poly[2-butoxy, 5-(2'-ethyl-hexyloxy-p-phenylene-vinylene] (BEH-PPV) and 0.20±0.05 for poly[2-methoxy, 5-(2'-ethyl-hexyloxy-p-phenylene-vinylene] (MEH-PPV), the most coiled derivative. Excitation profiles of the three derivatives also show an increase in nonradiative decay at high energies when the polymer assumes a more coiled comformation. Thus, the quantum yields are dependent on pump energy.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.468438
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Theoretical investigation of gas-phase torsion potentials along conjugated polymer backbones: polyacetylene, polydiacetylene, and polythiophene (1990)
    s.l. : American Chemical Society
    Macromolecules 23 (1990), S. 1150-1156 
    Details
    ISSN: 1520-5835
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ma00206a038
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    X-ray structural studies of poly(3-alkylthiophenes): an example of an inverse comb (1992)
    s.l. : American Chemical Society
    Macromolecules 25 (1992), S. 4364-4372 
    Details
    ISSN: 1520-5835
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ma00043a019
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    Paper (German National Licenses)
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  • 4
    Electronic Resource
    Electronic Resource
    Electroluminescence and electrical transport in poly(3-octylthiophene) diodes (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 72 (1992), S. 564-568 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report visible light emission from diodes made from poly(3-octylthiophene). Use of a soluble derivative of polythiophene allows fabrication of the light emitting diodes by casting the polymer film from solution with no subsequent processing or heat treatment required. The devices emit dim red-orange light with relatively low external quantum efficiencies, below 2.5×10−5 photons per electron at room temperature. Electrical characterization reveals diode behavior with rectification ratios greater than 102. The temperature dependence indicates that tunneling phenomena dominate the charge injection.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.351834
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  • 5
    Electronic Resource
    Electronic Resource
    Light-emitting diodes from partially conjugated poly(p-phenylene vinylene) (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 5177-5180 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report the effect of conversion conditions on the device characteristics of poly(p-phenylene vinylene) (PPV) light-emitting diodes. Both electroluminescence and photoluminescence intensities decrease with increasing degree of conversion. Partial conjugation enhances the electroluminescence intensity and gives an efficiency (with Ca as electron-injecting contact) as high as 0.75% photons per electron, about two orders of magnitude more efficient than from similar devices prepared from fully converted PPV. The results of constant current stress measurements suggest that the partially conjugated PPV diode is relatively stable at room temperature.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.353794
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    Paper (German National Licenses)
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  • 6
    Electronic Resource
    Electronic Resource
    Time-resolved photoluminescence from poly[2-methoxy, 5-(2'-ethyl-hexyloxy)-p-phenylene-vinylene]: Solutions, gels, films, and blends (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 98 (1993), S. 6504-6509 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present the results of time-resolved luminescence studies of poly[2-methoxy, 5-(2'-ethyl-hexyloxy)-p-phenylene-vinylene] (MEH-PPV), as a pure film, in solution, in a gel formed by a network of ultrahigh molecular weight polyethylene (UHMW-PE), and in a blend with UHMW-PE. The luminescence has a characteristic lifetime of 200–300 ps at room temperature, increasing to 500–700 ps when the materials are cooled to 80 K; the decay time is approximately the same for all the physical forms of the material (solution, film, gel, blend). The relatively short lifetimes, compared to intrinsic values calculated from absorption and emission spectra, and the observed temperature dependence indicate that the luminescence decay is quenched by nonradiative processes. The time decay of the photoluminescence deviates from a single exponential for most forms of the MEH-PPV. Best fits to stretched exponential and double exponential expressions are presented. Steady state photoluminescence spectra and integrated luminescence vs pump intensity data are presented in order to establish which of the possible mechanisms are most important.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.464790
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    Paper (German National Licenses)
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  • 7
    Electronic Resource
    Electronic Resource
    Soluble conjugated polymers with degenerate ground state derivatives of poly(1,6-heptadiyne) (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 99 (1993), S. 590-596 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We report the results of initial measurements on two derivatives of poly(1,6-heptadiyne): a di-ketone (PHDK) and a di-ester (PHDE). Both polymers have the degenerate ground state of poly(1,6-heptadiyne); both are soluble in common organic solvents. Electron spin resonance (ESR) measurements on pristine samples place an upper limit of 10−4 spins per monomer for both polymers. At low doping levels, we observe a single doping-induced absorption band at an energy of approximately half the π−π* gap, Eg/2; the doping-induced spectral features were fully reversible. In situ ESR and absorption measurements during doping show that charge is stored predominantly in spinless charge carriers. Because of the inequivalent carbons on the conjugated backbone, the results are discussed in terms of the (A=B)n polymer. Both PHDK and PHDE are relatively stable in air; the strength of the π−π* absorption band is nearly constant over a period of a week in air, decreasing to 80% of the initial value.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.465785
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    Paper (German National Licenses)
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  • 8
    Electronic Resource
    Electronic Resource
    Fine tuning of the band gap in conjugated polymers via control of block copolymer sequences (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 97 (1992), S. 2750-2758 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present the results of the Austin-Model 1 (AM1) geometry optimizations and valence effective Hamiltonian (VEH) band-structure calculations aimed at determining the evolution of the geometric structure and electronic properties (ionization potentials, electron affinities, band gaps) as a function of unit cell content in two sets of regular block copolymers. The first set consists of poly(p-phenylene vinylene)/poly(2,5-dimethoxy-1, 4-phenylene vinylene) copolymers, the second set of poly(p-phenylene)/polyacetylene copolymers. In the latter case, the band gap can be tuned over the whole visible range, depending on the extent of the block copolymer sequences. Special attention is paid to the possible occurrence of localization phenomena.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.463065
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    Paper (German National Licenses)
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  • 9
    Electronic Resource
    Electronic Resource
    Absorption spectroscopy of nonlinear excitations in polyaniline (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 98 (1993), S. 2664-2669 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present near steady state photoinduced absorption spectra of two forms of polyaniline. Both the emeraldine base (nondegenerate ground state) and pernigraniline (degenerate ground state) exhibit long lived photoinduced nonlinear excitations with transient absorptions within the π→π* gap. In the case of the emeraldine base, two well-resolved photoinduced absorption bands are observed with maxima at 0.9 and 1.47 eV, accompanied by a bleaching of the 2 eV absorption edge. The different relaxation rates of the two bands indicate that they arise from two independent photoinduced nonlinear excitations. The results are discussed in terms of intrachain and interchain excitations. The possibility of deep traps on defect sites in pernigraniline is suggested.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.464147
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    Paper (German National Licenses)
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  • 10
    Electronic Resource
    Electronic Resource
    Visible light emission from semiconducting polymer diodes (1991)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 58 (1991), S. 1982-1984 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report visible light emission from Shottky diodes made from semiconducting polymers, confirming the discovery by the Cambridge group [Nature 347, 539 (1990)]. Our results demonstrate that light-emitting diodes can be fabricated by casting the polymer film from solution with no subsequent processing or heat treatment required. Electrical characterization reveals diode behavior with rectification ratios greater than 104. We propose that tunneling of electrons from the recitifying metal contact into the gap states of the positive polaron majority carriers dominates current flow and provides the mechanism for light emission.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.105039
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