Novel dendritic large molecules as solution-processable thermally activated delayed fluorescent emitters for simple structured non-doped organic light emitting diodes

Solution-processable thermally activated delayed fluorescence (TADF)-assisted materials have been identified as promising materials for future applications as organic light-emitting diodes (OLEDs) owing to their numerous advantageous such as easy fabrication, large area applications, low cost, and state-of-the-art performance. Herein, two new carbazole-dendronized TADF emitters, namely, TB2CZ-ACTRZ and TB14CZ-ACTRZ, were designed and synthesized. Two different-sized carbazole dendron wedges were utilized as the encapsulating groups for the TADF core via methylene groups. The influence of the encapsulated dendrons on the thermal, optical, electrochemical, and OLED device performances of both dendritic molecules was studied in detail. The photophysical studies of TB2CZ-ACTRZ and TB14CZ-ACTRZ disclosed their extremely small singlet-triplet energy gaps (Delta E-ST) of 79 and 134 meV, respectively. Consequently, the solution-processed non-doped OLEDs without any hole injection/transport layers featuring TB2CZ-ACTRZ and TB14CZ-ACTRZ as the TADF emitters demonstrated the maximum external quantum efficiencies (EQEs) of 9.5 and 8.1%, respectively, while the device fabricated with their simple emissive core ACTRZ had an EQE of only 1.2%. These results clearly demonstrated that the development of multifunctional TADF dendritic emitters is an extremely worthwhile objective for the realization of highly efficient solution-processable non-doped OLEDs with simple device architectures.