Unique Solid-State Emission Behavior of Aromatic Difluoroboronated ß-Diketones as an Emitter in Organic Light-Emitting Devices.

Aromatic difluoroboronated ß-diketone (BF2 DK) derivatives are a widely known class of luminescent organic materials that exhibit high photoluminescent quantum efficiency and unique aggregation-dependent fluorescence behavior. However, there have been only a few reports on their use in solid-state electronic devices, such as organic light-emitting devices (OLEDs). Herein, we investigated the solid-state properties and OLED performance of a series of π-extended BF2 DK derivatives that have previously been shown to exhibit intense fluorescence in the solution state. The BF2 DK derivatives formed exciplexes with a carbazole derivative and exhibited thermally activated delayed fluorescence (TADF) behavior to give orange electroluminescence with a peak external quantum efficiency of 10 % that apparently exceeds the theoretical efficiency limit of conventional fluorescent OLEDs (7.5 %), assuming a light out-coupling factor of 30 %.