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Browsing by Author "Jakka, K"

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    Enhancing the thermal and spectral stabilities of polyfluorene-based bluelight-emitting materials by incorporating pendent spiro-cycloalkyl groups
    (2004-05-20)
    Wu, FI
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    Dodda, R
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    Jakka, K
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    Huang, JH
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    Hsu, CS
    We have synthesized polyfluorene-based copolymers containing spiro-cycloalkyl groups functionalized on the C-9 position of alternate fluorene units using the Suzuki coupling reaction. The presence of the rigid spiro-cycloalkyl pendent groups not only hinders the close packing and intermolecular interactions between polymer chains, but also preserves the molecular rigidity of the polymer, leading to polyfluorenes with high glass transition temperatures and improved thermal and spectral stabilities. The results of photoluminescence measurements of the isothermally heated spiro-polyfluorene thin films (150degreesC for 20h) show that the commonly observed aggregate/excimer formation is suppressed effectively in these polymers. Blue electroluminescence was demonstrated in a double-layer LED device using the spiro-derivatized polyfluorene as the emitting layer. (C) 2004 Elsevier Ltd. All rights reserved.
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    Synthesis and characterization of spiro(adamantane-2,9 '-fluorene)-based triaryldiamines: thermally stable hole-transporting materials
    (2004-06-03)
    Chen, CH
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    Shen, WJ
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    Jakka, K
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    Shu, CF
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    應用化學系
    New triaryldiamines. Adm-TPD and Adm-NPD, which contain a spiro(adamantane-2,9-fluorene) core, have been synthesized and characterized. We believe that because of the presence of the rigid spiro-fluorene core, these triaryldiamines exhibit higher glass transition temperatures and have a less tendency to crystallize relative to their biphenyl analogs. Additionally, electrochemical studies showed that the planarity of the fluorene core leads to lower ionization potentials and greater degrees of pi conjugation between the two amino groups. AFM measurements demonstrated that high-quality amorphous films of Adm-NPD with good morphological stability were prepared by vapor deposition. Electroluminescent devices using Adm-NPD as a hole-transporting layer-i.e., having the configuration ITO/Adm-NPD/Alq(3)/LiF/Al-emit a bright green light that is characteristic of Alq(3). (C) 2003 Elsevier B.V. All rights reserved.