15H-Diindolo[2,3-b1′,2′,3′-lm]carbazole: A novel rigid donor for highly efficient thermally activated delayed fluorescence emitters

In this contribution, we report a novel rigid 15H-diindolo[2,3-b:1′,2′,3′-lm]carbazole (DICz) donor for designing efficient thermally activated delayed fluorescence emitters named 2-(15H-diindolo[2,3-b:1′,2′,3′-lm]carbazol-15-yl)-5-(4,6-diphenyl-1,3,5-triazin-2)benzonitrile (DICzCNTrz) and unravelled its effects on the physicochemical and electroluminescence properties by comparing it with the control molecule, 2-(9H-carbazol-9-yl)-5-(4,6-diphenyl-1,3,5-triazin-2-yl)benzonitrile (CzCNTrz) featuring a carbazole donor. The photophysical properties revealed that the DICzCNTrz showed small singlet-triplet energy splitting, short delayed fluorescence exciton lifetime and high photoluminescence quantum yield when compared to CzCNTrz. The organic light emitting diode fabricated using the DICzCNTrz-based emitter exhibited superior performance with EQE of 21.4% and reduced efficiency roll-off at high brightness when compared to the device with the CzCNTrz-based emitter, which showed maximum EQE of 13.9%.