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  • 1
    Online Resource
    Online Resource
    On the angular dependence of the optical polarization anisotropy in ladder-type polymers
    AIP Publishing ; 2008
    In:  The Journal of Chemical Physics Vol. 128, No. 4 ( 2008-01-28)
    Details
    In: The Journal of Chemical Physics, AIP Publishing, Vol. 128, No. 4 ( 2008-01-28)
    Abstract: Two ladder-type polymers have been examined using polarized optical absorption and fluorescence spectroscopy in solution and solid state. The fluorescence anisotropy excitation spectra of ladder-type methyl-substituted poly(para-phenylene) and poly(naphthylene-phenylene) follow their absorption profiles, contrary to the typical behavior in other conjugated polymers, which show excitation wavelength dependent anisotropy until the onset of the typical red edge effect. Using Raman microscopy and linear dichroism of aligned stretched polyethylene films containing the ladder polymer, it has been found that the orientation of the absorption transition dipole moment is dependent on the conjugation length. The transition dipole of the shorter conjugation lengths of the distribution is localized approximately 7° off axis, and that of the longer conjugation lengths is delocalized along the chain.
    Type of Medium: Online Resource
    ISSN: 0021-9606 , 1089-7690
    URL: Article
    DOI: 10.1063/1.2822273
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2008
    detail.hit.zdb_id: 3113-6
    detail.hit.zdb_id: 1473050-9
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  • 2
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    Online Resource
    Inkjet printed polymer light-emitting devices fabricated by thermal embedding of semiconducting polymer nanospheres in an inert matrix
    AIP Publishing ; 2008
    In:  Applied Physics Letters Vol. 92, No. 18 ( 2008-05-05)
    Details
    In: Applied Physics Letters, AIP Publishing, Vol. 92, No. 18 ( 2008-05-05)
    Abstract: An aqueous dispersion of semiconducting polymer nanospheres was used to fabricate polymer light-emitting devices by inkjet printing in an easy-to-apply process with a minimum feature size of 20μm. To form the devices, the electroluminescent material was printed on a nonemitting polystyrene matrix layer and embedded by thermal annealing. The process allows the printing of light-emitting thin-film devices without extensive optimization of film homogeneity and thickness of the active layer. Optical micrographs of printed device arrays, electroluminescence emission spectra, and I∕V characteristics of printed ITO/PEDOT:PSS/PS/SPN/Al devices are presented.
    Type of Medium: Online Resource
    ISSN: 0003-6951 , 1077-3118
    URL: Article
    DOI: 10.1063/1.2921780
    RVK:
    UA 1000
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2008
    detail.hit.zdb_id: 211245-0
    detail.hit.zdb_id: 1469436-0
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  • 3
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    Online Resource
    Triplet-triplet annihilation in a poly(fluorene)-derivative
    AIP Publishing ; 2001
    In:  The Journal of Chemical Physics Vol. 115, No. 21 ( 2001-12-01), p. 10007-10013
    Details
    In: The Journal of Chemical Physics, AIP Publishing, Vol. 115, No. 21 ( 2001-12-01), p. 10007-10013
    Abstract: We report on measurements of phosphorescence (Ph) and delayed fluorescence (DF) in poly(2,7-(9,9-bis(2-ethylhexyl)fluorene)) (PF2/6) present as dilute solid solution, as well as in bulk films. From combined experimental investigations of the time and intensity dependence of DF and Ph, as well as the temperature dependence of DF, we are able to show that DF in PF2/6, both in solution and film, is dominated by triplet-triplet annihilation (TTA). As a consequence of the intrachain diffusion and, hence, relaxation of triplets, the kinetics of the bimolecular reaction show a turnover from dispersive to nondispersive regime as borne out by the DF decay. This is in accord with theoretical predictions of TTA in disordered solids. From the transition to equilibrium kinetics, we are able to estimate the width of the density of states of triplets to 40 meV in good agreement with the width of the inhomogeneous broadenend S0←T1 transition of PF2/6.
    Type of Medium: Online Resource
    ISSN: 0021-9606 , 1089-7690
    URL: Article
    DOI: 10.1063/1.1415446
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2001
    detail.hit.zdb_id: 3113-6
    detail.hit.zdb_id: 1473050-9
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  • 4
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    Online Resource
    Intrachain exciton quenching analysis in conjugated polymers by two-photon spectroscopy
    AIP Publishing ; 2002
    In:  The Journal of Chemical Physics Vol. 116, No. 8 ( 2002-02-22), p. 3449-3454
    Details
    In: The Journal of Chemical Physics, AIP Publishing, Vol. 116, No. 8 ( 2002-02-22), p. 3449-3454
    Abstract: Intrachain exciton quenching in ladder-type polyparaphenylene has been quantified for the first time. Two-phonon absorption and subsequent upconverted photoluminescence of ladder-type polyparaphenylene and polyfluorene has been measured and analyzed with a new theoretical framework for the two-photon absorption saturation. This microscopic analysis determines the number of singlet excitons as a function of the excitation intensity, which is compared to the photoluminescence intensity. The absorption saturation alone perfectly describes the photoluminescence saturation in polyfluorene, whereas in ladder-type polyparaphenylene, exciton–exciton quenching occurs. By measuring in solution, the formation of stacked polymer chains is prevented. Therefore, the quenching is due to intrachain interaction.
    Type of Medium: Online Resource
    ISSN: 0021-9606 , 1089-7690
    URL: Article
    DOI: 10.1063/1.1445108
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2002
    detail.hit.zdb_id: 3113-6
    detail.hit.zdb_id: 1473050-9
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  • 5
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    Online Resource
    Xerographic study on a ladder-type poly(para-phenylene)
    AIP Publishing ; 2000
    In:  The Journal of Chemical Physics Vol. 112, No. 9 ( 2000-03-01), p. 4305-4309
    Details
    In: The Journal of Chemical Physics, AIP Publishing, Vol. 112, No. 9 ( 2000-03-01), p. 4305-4309
    Abstract: Photogeneration of charge carriers in a methyl-substituted ladder-poly(para-phenylene) (LPPP) has been investigated by xerographic experiments. The quantum efficiency of charge carrier generation was calculated by evaluating the photoinduced discharge curves (PIDCs) and found to be independent of both excitation wavelength and temperature. The results can be described by a modified Braun theory with a simple exponential distribution of radii of thermalized electrons. LPPP shows a very high primary quantum efficiency of 80%, a low residual potential, and a small dark decay. Thus, LPPP represents a promising material to build single component single-layer photoreceptors.
    Type of Medium: Online Resource
    ISSN: 0021-9606 , 1089-7690
    URL: Article
    DOI: 10.1063/1.480976
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2000
    detail.hit.zdb_id: 3113-6
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  • 6
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    Online Resource
    Long lived photoexcitation dynamics in a dendronically substituted poly(fluorene)
    AIP Publishing ; 2003
    In:  The Journal of Chemical Physics Vol. 119, No. 13 ( 2003-10-01), p. 6904-6910
    Details
    In: The Journal of Chemical Physics, AIP Publishing, Vol. 119, No. 13 ( 2003-10-01), p. 6904-6910
    Abstract: Polyfluorenes are possibly the most attractive class of conjugated polymers for blue polymer light emitting devices. Derivatives with dendron side chains have been found to significantly improve the color stability of the devices. Using a quasi-cw photoinduced absorption technique we present a qualitative and quantitative analysis of lifetimes and deactivation mechanisms for the triplet excited states in a dendronically substituted derivative. The triplet lifetimes increase by one order of magnitude in the dendronic derivative compared to those in a standard poly(dialkylfluorene), which has been characterized for comparison. The temperature dependence of triplet lifetimes is interpreted in terms of migration assisted deactivation of triplet excitations. We conclude that the dendrons inhibit the Dexter-transfers of triplet excitations between the polymer chains and so strongly hinder triplet migration.
    Type of Medium: Online Resource
    ISSN: 0021-9606 , 1089-7690
    URL: Article
    DOI: 10.1063/1.1603723
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2003
    detail.hit.zdb_id: 3113-6
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  • 7
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    Online Resource
    Energy and charge transfer in blends of dendronized perylenes with polyfluorene
    AIP Publishing ; 2008
    In:  The Journal of Chemical Physics Vol. 129, No. 11 ( 2008-09-21)
    Details
    In: The Journal of Chemical Physics, AIP Publishing, Vol. 129, No. 11 ( 2008-09-21)
    Abstract: Two generations of polyphenylene dendrimers with a perylene diimide core are compared with a nondendronized tetraphenoxyperylene diimide model compound regarding their application in organic light-emitting diodes (OLEDs). Single layer devices with blends of the first and second generation dendrimers in polyfluorene are investigated as active layers in OLEDs, and the effect of dendronization on the emission color and electroluminescence intensity is studied. In photoluminescence, higher degrees of dendronization lead to a reduction in Förster transfer from the polyfluorene host to the perylene, resulting in a larger contribution of the blue host emission in the photoluminescence spectra. In electroluminescence, the dopants appear to act as active traps for electrons, resulting in a predominant generation of excitons on the dye. This gives rise to a remarkably stronger contribution of red emission in electroluminescence than in photoluminescence where energy is exchanged exclusively via Förster transfer. The pronounced color change from red to blue with higher degrees of dendronization and larger driving voltages is explained by the competition of the recombination of free electrons with holes and trapping of electrons by the emitting guest.
    Type of Medium: Online Resource
    ISSN: 0021-9606 , 1089-7690
    URL: Article
    DOI: 10.1063/1.2976769
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2008
    detail.hit.zdb_id: 3113-6
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  • 8
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    Cryptand based solid-state electrolytes in polymer light-emitting devices
    AIP Publishing ; 2007
    In:  Applied Physics Letters Vol. 91, No. 13 ( 2007-09-24)
    Details
    In: Applied Physics Letters, AIP Publishing, Vol. 91, No. 13 ( 2007-09-24)
    Abstract: In order to gain improved insight into the fundamental mode of operation of light-emitting electrochemical cells (LECs), LECs were prepared from a solid-state electrolyte, consisting of the cryptand (Kryptofix® 222, [2.2.2] cryptand) and lithium triflate, and a blue emitting low-Stokes-shift poly(para-phenylene). The devices reveal LEC-like characteristics, however, their evolution appear on a longer time scale, which is a consequence of reduced cation conductivity of the [2.2.2] cryptands compared to commonly used ion conductors and decelerated electrochemical n doping near the cathode. It is possible to study the location and direction of the emission zone shift during device operation.
    Type of Medium: Online Resource
    ISSN: 0003-6951 , 1077-3118
    URL: Article
    DOI: 10.1063/1.2773756
    RVK:
    UA 1000
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2007
    detail.hit.zdb_id: 211245-0
    detail.hit.zdb_id: 1469436-0
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  • 9
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    Direct observation of state-filling at hybrid tin oxide/organic interfaces
    AIP Publishing ; 2019
    In:  Applied Physics Letters Vol. 114, No. 18 ( 2019-05-06)
    Details
    In: Applied Physics Letters, AIP Publishing, Vol. 114, No. 18 ( 2019-05-06)
    Abstract: Electroluminescence (EL) spectra of hybrid charge transfer states at metal oxide/organic type-II heterojunctions exhibit bias-induced spectral shifts. The reasons for this phenomenon have been discussed controversially and arguments for either electric field-induced effects or the filling of trap states at the oxide surface have been put forward. Here, we combine the results of EL and photovoltaic measurements to eliminate the unavoidable effect of the series resistance of inorganic and organic components on the total voltage drop across the hybrid device. For SnOx combined with the conjugated polymer [ladder type poly-(para-phenylene)], we find a one-to-one correspondence between the blueshift of the EL peak and the increase of the quasi-Fermi level splitting at the hybrid heterojunction, which we unambiguously assign to state filling. Our data are resembled best by a model considering the combination of an exponential density of states with a doped semiconductor.
    Type of Medium: Online Resource
    ISSN: 0003-6951 , 1077-3118
    URL: Article
    DOI: 10.1063/1.5082704
    RVK:
    UA 1000
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2019
    detail.hit.zdb_id: 211245-0
    detail.hit.zdb_id: 1469436-0
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  • 10
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    Online Resource
    Enhanced feedback in organic photonic-crystal lasers
    AIP Publishing ; 2005
    In:  Applied Physics Letters Vol. 87, No. 15 ( 2005-10-10)
    Details
    In: Applied Physics Letters, AIP Publishing, Vol. 87, No. 15 ( 2005-10-10)
    Abstract: The mode coupling of organic lasers is greatly enhanced by a photonic crystal that consists of a thin layer of titanium dioxide (TiO2) with a rectangular lattice of holes. The use of TiO2 increases the index contrast in the photonic crystal as well as the confinement in the waveguide, which results in larger feedback given to the lasing modes. This in turn leads to lower thresholds and much smaller devices. Vertically emitting laser devices have been fabricated according to optimized parameters, and the spectral features measured are in excellent agreement with simulations. The devices feature a three to five times lower threshold than devices whose feedback structure is etched directly into the fused silica substrate.
    Type of Medium: Online Resource
    ISSN: 0003-6951 , 1077-3118
    URL: Article
    DOI: 10.1063/1.2103396
    RVK:
    UA 1000
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2005
    detail.hit.zdb_id: 211245-0
    detail.hit.zdb_id: 1469436-0
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