Aggregation-Enhanced Emission and Thermally Activated Delayed Fluorescence of Derivatives of 9-Phenyl-9H-Carbazole: Effects of Methoxy and tert-Butyl Substituents

Derivatives of 9-phenyl-9H-carbazole were synthesized as efficient emitters exhibiting both thermally activated delayed fluorescence and aggregation-induced emission enhancement. Effects of methoxy and tert-butyl substituents at the different positions of carbazolyl groups on the properties of the emitters were studied. Depending on the substitutions, photoluminescence quantum yields (PLQY) of non-doped solid films of the compounds ranged from 17% to 53% which were much higher than those observed for the solutions in low-polarity solvent toluene. Compounds substituted at C-3 and C-6 positions of carbazole moiety by methoxy- and tert-butyl- groups showed the highest solid-state PLQY. Ionization potentials of the studied derivatives in solid-state were found to be in the short range of 5.75-5.89eV. Well-balanced hole and electron mobilities were detected for tert-butyl-substituted compound. They exceeded 10(-4)cm(2)(Vxs)(-1) at electric fields higher than 3x10(5)Vcm(-1). Two compounds with the highest solid-state PLQYs showed higher efficiencies in non-doped organic light-emitting diodes than in the doped devices. Maximum external quantum efficiency of 7.2% and brightness of 15000cdm(-2) were observed for the best device.