Novel hole transport materials based on N,N′-disubstituted-dihydrophenazine derivatives for electroluminescent diodes†
Abstract
A series of novel hole transport materials for organic light-emitting diodes (OLEDs) based on 9,14-diphenyl-9,14-dihydrodibenzo[a,c]phenazine were synthesized and characterized by 1H NMR and 13C NMR, mass spectrometry and single crystal structure analysis methodologies. The crystal structures of three selected molecules reveal large dihedral angles between different functional units. The electro-optical properties of the materials were examined by UV-vis absorption, photoluminescence spectroscopy and cyclic voltammetry. The HOMO of the materials were between 4.83–5.08 eV, indicating a good match between the HOMO of indium tin oxide (ITO) and the HOMO of light-emitting layer, which renders the promising candidates as hole transport materials for organic light-emitting devices. In terms of the device with the structure of ITO/HTM (60 nm)/Alq3 (50 nm)/LiF (1 nm)/Al (200 nm), the device b using N,N-diphenyl-4′-(14-phenyldibenzo[a,c]phenazin-9(14H)-yl)-[1,1′-biphenyl]-4-amine presented a maximum luminance of 17 437 cd m−2 at 10.7 V and kept a high current efficiency (the maximum current efficiency is 2.25 cd A−1) at a high current density (>500 mA cm−2), which illustrates the exploited material possesses good hole transport and stable properties.