Synthesis, Structure, Properties, and Application of a Carbazole-Based Diaza[7]helicene in a Deep-Blue-Emitting OLED

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 (Td=372.1?degrees C) and a high glass-transition temperature (Tg, up to 203.0?degrees 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 LEclairage (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.