Molecular topology tuning of bipolar host materials composed of fluorene-bridged benzimidazole and carbazole for highly efficient electrophosphorescence.
Chemistry
; 19(32): 10563-72, 2013 Aug 05.
Article
em En
| MEDLINE
| ID: mdl-23788214
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 Câ
connectivity between phenylbenzimidazole and the fluorene bridge exhibited extended πâ
conjugation; therefore, a low triplet energy of 2.52â
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 (2.72â
eV) of CzFNBI imparted by the Nâ
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 %, 36.3â
cd A(-1) , 28.3â
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 12â
V, and a high color-rendering index of 91.6.
Texto completo:
1
Coleções:
01-internacional
Base de dados:
MEDLINE
Idioma:
En
Revista:
Chemistry
Assunto da revista:
QUIMICA
Ano de publicação:
2013
Tipo de documento:
Article
País de afiliação:
Taiwan