Starting from 1-iodo-4-methylbenzene, hexaphenylbenzene-based organic compounds 1, 2, 3, 4 and 5 were synthesized as electroluminescent materials via a five-step synthetic route. The structures of those compounds were confirmed through 1H, 13C-NMR and FT-IR spectrums. The fluorescence spectra of the compounds 1, 2 and 3 showed a stable blue light-emitting behavior in the solution state. Cyclic voltammetry(CV) studies revealed that compounds 1, 2 and 3 had high electrochemical stabilities and the CV data also showed that the HOMO energy levels for the molecules are close to the work functions of anode materials such as ITO, indicating a favorable hole transport property of the molecules. Using compounds 1, 2 and 3, three types of EL devices were fabricated, which consisted of ITO/HTL/EML/
ETL/Al:Li, ITO/HTL/EML/HBL/ETL/Al:Li and ITO/HTL/ETL/Al:Li, respectively. The type I devices using compounds as an EML gave green electroluminescence, the type II devices using compounds as an EML showed that compounds 1 and 2 were not suitable for light emitting layer, and the type III devices using compounds as a HTL showed hole transport property. Comparing with NPD, type III EL devices using compounds 1 and 3 showed good hole transport property.
The molecular structures of the compounds synthesized in this research are given as follows.