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Please use this identifier to cite or link to this item: http://ntour.ntou.edu.tw:8080/ir/handle/987654321/41280

Title: Molecular Topology Tuning of Bipolar Host Materials Composed of Fluorene-bridged Benzimidazole and Carbazole for Highly Efficient Electrophosphorescence
Authors: Ming-Hung Cheng
Ken-Tsung Wong
Yang-Huei Chen
Wen-Yi Hung
Contributors: 國立臺灣海洋大學:光電科學研究所
Keywords: photochemistry
electrophosphorescence
bipolar hosts
luminescence
organic light-emitting devices
Date: 2013
Issue Date: 2017-02-13T08:43:17Z
Publisher: Chemistry-A European Journal
Abstract: Abstract: Two new molecules, CzFCBI and CzFNBI, have been tailor-made to serve as bipolar host materials to realize high-efficiency electrophosphorescent devices. The molecular design is configured with carbazole as the hole-transporting block and N-phenylbenzimidazole as the electron-transporting block hybridized through the saturated bridge center (C9) and meta-conjugation site (C3) of fluorene, respectively. With structural topology tuning of the connecting manner between N-phenylbenzimidazole and the fluorene core, the resulting physical properties can be subtly modulated. Bipolar host CzFCBI with a C connectivity between phenylbenzimidazole and the fluorene bridge exhibited extended π conjugation; therefore, a low triplet energy of 2.52 eV was observed, which is insufficient to confine blue phosphorescence. However, the monochromatic devices indicate that the matched energy-level alignment allows CzFCBI to outperform its N-connected counterpart CzFNBI while employing other long-wavelength-emitting phosphorescent guests. In contrast, the high triplet energy (2.72 eV) of CzFNBI imparted by the N connectivity ensures its utilization as a universal bipolar host for blue-to-red phosphors. With a common device configuration, CzFNBI has been utilized to achieve highly efficient and low-roll-off devices with external quantum efficiency as high as 14 % blue, 17.8 % green, 16.6 % yellowish-green, 19.5 % yellow, and 18.6 % red. In addition, by combining yellowish-green with a sky-blue emitter and a red emitter, a CzFNBI-hosted single-emitting-layer all-phosphor three-color-based white electrophosphorescent device was successfully achieved with high efficiencies (18.4 %, 36.3 cd A(-1) , 28.3 lm W(-1) ) and highly stable chromaticity (CIE x=0.43-0.46 and CIE y=0.43) at an applied voltage of 8 to 12 V, and a high color-rendering index of 91.6.
Relation: 19(32)
URI: http://ntour.ntou.edu.tw:8080/ir/handle/987654321/41280
Appears in Collections:[光電科學研究所] 期刊論文

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