Dual Thermally Activated Delayed Fluorescence from a Single Carbazole Derivative with Multiple Charge Transfer Pathways

Two carbazole derivatives BPA-BNC and 4BPABNC are designed and synthesized to explore the probable dualemission behavior and mechanisms. BPA-BNC contains two arylamino donors and one B-N multi-resonance (MR) segment at 3,6,9-positions of a single carbazole, while 4BPABNC has two extraarylamine donors at 1,8-positions in addition to the above substituent groups. Two compounds in polar solvents show a clear dual emission peaked at near 490 and 540 nmwith high photoluminescence quantum yields of up to 98 %, short delayed lifetimesand extremely small single-triplet splitting energies. The dual emissions originate fromthe MR and through-bond charge transfer transitions, which are supported by theoretical calculation and experimental data. The solution-processed devices based on BPA-BNC and 4BPABNC also exhibit dual emissions and achieve the maximum external quantum efficiencies(EQEs) of 13.1 %and 12.7 %, whereas the model MR molecule provides an EQE of 7.3 % under the same device architecture.