Blue-to-Green Fine-Tunable Narrowband Delayed Fluorescence in Peripherally Dendritic Modified Bis-Indolocarbazoles

Highly efficient narrowband organic luminophores offer immense potentials for organic light-emitting diodes (OLEDs) with high color purity of electroluminescence (EL). Appropriately controlling their structural relaxation and vibronic couplings between the excited and ground states enables the desired narrowband emissions. Herein, based on a design concept featuring dendritic modifications, we demonstrate the exquisite color tuning of narrowband emissions from deep blue to green in non-boron ubiquitous molecular systems. By attaching two or four arylamine-based dendritic units to the periphery of the indolo[3,2,1-jk]indolo[1',2',3':1,7]indolo[3,2-b]carbazole (BICz) core, BICz-1.5G, BICz-2G, and BICz-2GII were developed as deep-blue, sky-blue, and green narrowband emitters, respectively. Comprehensive photophysical and computational studies revealed that the dendritic modifications do not impair the inherent narrowband emission ability of BICz while enhancing its thermally activated delayed fluorescence properties. OLEDs incorporating BICz-1.5G and BICz-2GII demonstrated high-efficiency, high-color-purity blue and green EL, with maximum external quantum efficiencies as high as 24.0% and 28.5%, respectively, and CIE coordinates of (0.13, 0.10) and (0.21, 0.68). Our findings will contribute to expanding the search space for narrowband organic luminophores.