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.