Multi-substituted dibenzo[a, c]phenazine derivatives as solution-processable thermally activated delayed fluorescence materials for orange red organic light-emitting diodes

Highly efficient solution-processable emitters, especially long-wavelength (orange-to-red) emitters, are greatly desired to develop low-cost and low-energy-consumption organic light-emitting diodes (OLEDs). Here, a new series of luminescent dibenzo[a,c]phenazine derivatives with aromatic amine-substituted donor units, have been synthesized and reported as thermally activated delayed fluorescent (TADF) emitters. The combination of highly rigid molecular architecture and pretwisted charge transfer states endow these emitters with relatively high photoluminescence quantum yields (PLQYs) and small energy gap (Delta E-ST). By tuning the electron-donating capabilities of the donor as well as the amount of donor unit, the photophysical properties of these emitters in films can be systematically regulated, with emissions ranging from green to red. Multi-substituted construction strategy pledge a high moleculer-weight distribution to functionalize these emitters to form a uniform thin film via a solution process. Consequently, DBP-4MOTPA can afford a high orange-red TADF OLED by solution process with external quantum efficiencies of 10.2%, which is among the highest results of the reported solution-processed orange-red TADF OLEDs. Our results demonstrate that the marriage of regulating electron-donating capabilities and tuning the amount of donor unit is a rational strategy to design highly efficient long-wavelength TADF emitters.