3,3'-Bicarbazole structural derivatives as charge transporting materials for use in OLED devices

Abstract

In this study we report novel 3,3′-bicarbazole based charge transporting materials mainly designed for a use in systems containing phosphorescent iridium (III) complex emitters. A low-cost oxidative coupling reaction using FeCl3 was employed in the synthesis of 3,3′-bicarbazole compounds. Different derivatives of 3,3′-bicarbazole with 4-ethoxyphenyland ethyl- substituents at 9,9′- positions and (2,2-diphenylhydrazono)methyl- and 4-(dimethylamino)styryl- substituents at 6,6′- positions were synthesized. Obtained (2,2-diphenylhydrazono)methyl- derivatives exhibit glass transition temperatures that are sufficient for applications in electronic devices. Thin amorphous films of good optical quality can be produced from synthesized materials using spin-coating method. The effect of (2,2-diphenylhydrazono)methylsubstituents at 6,6′- and 4-ethoxyphenyl- substituents at 9,9′- positions on the charge transport properties of the 3,3′-bicarbazole derivatives was investigated. With the introduction of both electron acceptor and donor moieties to 3,3′-bicarbazole structure material electron and hole drift mobilities reach approximately 1·10-5 cm2/V·s. Molecule ionization (If) levels and electron affinity (EAf) levels in thin films were determined using photoelectric effect experiment. Depending on the nature of substituents at 6,6′- and 9,9′- positions If levels range from -5.19 to -5.13 eV and EAf levels are from -2.44 to -2.38 eV.