Encapsulated TADF macrocycles for high-efficiency solution-processed and flexible organic light-emitting diodes.

Macrocyclic thermally activated delayed fluorescence (TADF) emitters have been demonstrated to realize high efficiency OLEDs, but the design concept was still confined to rigid π-conjugated structures. In this work, two macrocyclic TADF emitters, Cy-BNFu and CyEn-BNFu, with a flexible alkyl chain as a linker and bulky aromatic hydrocarbon wrapping units were designed and synthesized. The detailed photophysical analysis demonstrates that the flexible linker significantly enhances the solution-processibility and flexibility of the parent TADF core without sacrificing the radiative transition and high PLQY. Moreover, benefiting from sufficient encapsulation of both horizontal and vertical space, the macrocyclic CyEn-BNFu further isolated the TADF core and inhibited the aggregation caused quenching, which benefits the utilization of triplet excitons. As a result, the non-doped solution-processed OLEDs based on CyEn-BNFu exhibit high maximum external quantum efficiencies (EQE) up to 32.3%, which were 3 times higher than those of the devices based on the parent molecule. In particular, these macrocyclic TADF emitters ensure the fabrication of flexible OLEDs with higher brightness, color purity and bending resistance. This work opens a way to construct macrocyclic TADF emitters with a flexible alkyl chain linker and highlights the benefits of such encapsulated macrocycles for optimizing the performance of flexible solution-processed devices.