Morphological stable spirobifluorene/oxadiazole hybrids as bipolar host materials for efficient green and red electrophosphorescence.
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 degrees C and 136-210 degrees 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 pi-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 1-3 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.
Tao
Youtian
Y
Department of Chemistry, Hubei Key Lab on Organic and Polymeric Optoelectronic Materials, Wuhan University, Wuhan 430072, People's Republic of China.
Ao
Liang
L
Wang
Qiang
Q
Zhong
Cheng
C
Yang
Chuluo
C
Qin
Jingui
J
Ma
Dongge
D
D004563:Electrochemistry; D005449:Fluorenes / Q000737:chemistry*; D008163:Luminescent Measurements; D008956:Models, Chemical; D015394:Molecular Structure; D010069:Oxadiazoles / Q000737:chemistry*; D013050:Spectrometry, Fluorescence; D013141:Spiro Compounds / Q000737:chemistry*
D005449:Fluorenes; D010069:Oxadiazoles; D013141:Spiro Compounds