title: Synthesis, structure, properties, and application of a carbazole-based diaza[7]helicene in a deep-blue-emitting OLED.
abstract: A carbazole-based diaza[7]helicene, 2,12-dihexyl-2,12-diaza[7]helicene (1), was synthesized by a photochemical synthesis and its use as a deep-blue dopant emitter in an organic light-emitting diode (OLED) was examined. Compound 1 exhibited good solubility and excellent thermal stability with a high decomposition temperature (T(d)=372.1 °C) and a high glass-transition temperature (T(g), up to 203.0 °C). Single-crystal structural analysis of the crystalline clathrate (1)(2)⋅cyclohexane along with a theoretical investigation revealed a non-planar-fused structure of compound 1, which prevented the close-packing of molecules in the solid state and kept the molecule in a good amorphous state, which allowed the optimization of the properties of the OLED. A device with a structure of ITO/NPB (50 nm)/CBP:5 % 1 (30 nm)/BCP (20 nm)/Mg:Ag (100 nm)/Ag (50 nm) showed saturated blue light with Commission Internationale de L'Eclairage (CIE) coordinates of (0.15, 0.10); the maximum luminance efficiency and brightness were 0.22 cd A(-1) (0.09 Lm W(-1)) and 2365 cd m(-2), respectively. This new class of helicenes, based on carbazole frameworks, not only opens new possibilities for utilizing helicene derivatives in deep-blue-emitting OLEDs but may also have potential applications in many other fields, such as molecular recognition and organic nonlinear optical materials.
authors.affiliation: State Key Laboratory of Crystal Materials, Shandong University, Jinan, 250100, PR China.
authors.forename: Longqiang
authors.initials: L
authors.lastname: Shi
authors.forename: Zhi
authors.initials: Z
authors.lastname: Liu
authors.forename: Guifang
authors.initials: G
authors.lastname: Dong
authors.forename: Lian
authors.initials: L
authors.lastname: Duan
authors.forename: Yong
authors.initials: Y
authors.lastname: Qiu
authors.forename: Jiong
authors.initials: J
authors.lastname: Jia
authors.forename: Wei
authors.initials: W
authors.lastname: Guo
authors.forename: Dan
authors.initials: D
authors.lastname: Zhao
authors.forename: Deliang
authors.initials: D
authors.lastname: Cui
authors.forename: Xutang
authors.initials: X
authors.lastname: Tao