Hole-transporting materials based on diarylfluorene compounds containing different substituents: DFT simulation, spectroscopic characterization and applications in organic light emitting diodes

Abstract Three diarylfluorene derivatives with phenyl, biphenyl, and naphthyl fragments were synthesized and characterized as electroactive materials of high thermal stability, which can form amorphous layers with glass transition temperatures of 31–74 °C. Systematic analysis of diarylfluorene compounds in the framework of the molecular charge redistribution processes according to quantum chemistry simulations allows concluding that a partially broken π-conjugated system of the core is related to the rotation motion of substituents which effectively modified the π-conjugated properties of fluorene core. The low-molar-mass derivatives, previously tested as hole transporting (HT) materials, were used in bilayer electroluminescent organic light emitting diodes with Alq3 as the emitter. The device with the HT layer of 2,7-di(1-naphthyl)-9,9-diethylfluorene exhibited the best overall performance as turn-on voltage of 4.6 V; maximum photometric efficiency of 2.8 cd A−1; maximum brightness about 7760 cd m−2.