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Morphological Stable Spirobifluorene/Oxadiazole Hybrids as Bipolar Host Materials for Efficient Green and Red Electrophosphorescence
Author(s) -
Tao Youtian,
Ao Liang,
Wang Qiang,
Zhong Cheng,
Yang Chuluo,
Qin Jingui,
Ma Dongge
Publication year - 2010
Publication title -
chemistry – an asian journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.18
H-Index - 106
eISSN - 1861-471X
pISSN - 1861-4728
DOI - 10.1002/asia.200900433
Subject(s) - oxadiazole , homo/lumo , phosphorescence , moiety , oled , thermal stability , materials science , photochemistry , quantum efficiency , thermal decomposition , chemistry , molecular orbital , molecule , optoelectronics , stereochemistry , fluorescence , layer (electronics) , organic chemistry , nanotechnology , physics , quantum mechanics
A series of 9,9′‐spirobifluorene/oxadiazole hybrids with various linkages between two components, namely SBF‐ p ‐OXD ( 1 ), SBF‐ m ‐OXD ( 2 ), and SBF‐ o ‐OXD ( 3 ) are designed and synthesized through Suzuki cross‐coupling reactions. The incorporation of a rigid and bulky spirobifluorene moiety greatly improves their thermal and morphological stability, with T d (decomposition temperature) and T g (glass transition temperature) in the ranges of 401–480 °C and 136–210 °C, respectively. 2 and 3 with meta ‐ and ortho ‐linkage display higher triplet energy and blue‐shifted absorption and emission than their para‐ linked analogue 1 owing to the decreasing π‐conjugation between the two components. Their HOMO and LUMO energy levels depend on the linkage modes within the range of 5.57–5.64 eV and 2.33–2.49 eV, respectively. Multilayer deep red electrophosphorescent devices with 1 , 2 , 3 as hosts were fabricated and their EL efficiencies follow the order of 3 ( o )> 2 ( m )> 1 ( p ), which correlates with their triplet energy and the separation of HOMO and LUMO distributions at molecular orbitals. The maximum external quantum efficiencies of 11.7 % for green and 9.8 % for deep red phosphorescent organic light‐emitting diodes (OLEDs) are achieved by using 2 and 3 as host materials, respectively.