New n-Type Organic Semiconductors: Synthesis, Single Crystal Structures, Cyclic Voltammetry, Photophysics, Electron Transport, and Electroluminescence of a Series of Diphenylanthrazolines

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Abstract
The synthesis, properties, and electroluminescent device applications of a series of five new diphenylanthrazoline molecules 1a − 1e are reported. Compounds 1b, 1c, and 1d crystallized in the monoclinic system with the space groups P21/c, C2/c, and P21/c, respectively, revealing highly planar molecules. Diphenylanthrazolines 1a − 1e have a formal reduction potential in the range −1.39 to −1.58 V (versus SCE) and estimated electron affinities (LUMO levels) of 2.90−3.10 eV. Compounds 1a − 1e emit blue light with fluorescence quantum yields of 58−76% in dilute solution, whereas they emit yellow-green light as thin films. The diphenylanthrazoline molecules as the emissive layers in light-emitting diodes gave yellow light with a maximum brightness of 133 cd/m2 and an external quantum efficiency of up to 0.07% in ambient air. Bilayer light-emitting diodes using compounds 1a − 1e as the electron-transport layer and poly(2-methoxy-5-(2‘-ethyl-hexyloxy)-1,4-phenylene vinylene) as the emissive layer had a maximum external efficiency of 3.1% and 2.0 lm/W and a brightness of up to 965 cd/m2 in ambient air. These results represent enhancements of up to 50 times in external quantum efficiency and 17 times in brightness when using 1a − 1e as the electron-transport materials in polymer light-emitting diodes. These results demonstrate that the new diphenylanthrazolines are promising n-type semiconductors for organic electronics.