A Series of Fused Carbazole/Carbonyl Based Blue to Yellow‐Green Thermally Activated Delayed Fluorescence Materials for Efficient Organic Light‐Emitting Diodes

Abstract The exploitation of novel fused carbazole/carbonyl emitters is essential to broaden the application of thermally activated delayed fluorescence (TADF) materials for organic light‐emitting diodes (OLEDs). Here, with the aid of the addition and cyclization of the cyano group with the ortho‐carbazole, fused carbazole/carbonyl based TADF emitters are effectively synthesized via this new synthetic strategy. The attachment of ancillary donors including carbazole, diphenylamine, and phenolazine to the fused carbazole/carbonyl skeletons further tunes their emissions from blue to yellow‐green. Particularly, pure‐blue OLEDs incorporating the peripheral carbazole attached emitter exhibit a maximum external quantum efficiency (EQE max ) of 22.3%, with a small full width at half maximum (FWHM) of 48 nm. In addition, the peripheral phenolazine attached yellow‐green emitter shows extremely small singlet−triplet state energy gap (Δ E ST ) of 0.01 eV, high photoluminescence quantum efficiency of 82.5%, short delayed fluorescence lifetime of 6.2 µs and good OLED performances with an EQE max of 21.7%, an FWHM of 68 nm and low efficiency roll‐off. These results demonstrate that the new synthetic strategy for fused carbazole/carbonyl molecules provide a valuable reference for the design of high‐efficient TADF emitters.