Single‐Molecule Architecture Engineering of n‐Type Host‐Fused Multi‐Resonance Emitters: Realizing Zero‐Radius Intramolecular Energy Transfer in Exciplex‐Based OLEDs

ABSTRACT The exciplex‐dopant in the emissive layer (EML) is employed in the organic light‐emitting diodes (OLEDs) to achieve high efficiency and operational stability. In particular, for efficient exciton energy transfer, the intermolecular distance between the host and dopant is a crucial factor. However, conventional exciplex‐dopant system emissive layers (EMLs) are composed of multiple components, such as mixed hosts and dopants, making it challenging to maintain efficient energy transfer in the manufacturing process. In this paper, blue fluorescent dopants (BFDs) fused with n‐type host molecules, DABNA‐Spiro‐2‐Trz and DABNA‐Spiro‐3‐Trz, were designed and synthesized. In the DABNA‐Spiro‐2‐Trz and DABNA‐Spiro‐3‐Trz molecules, the absence of intermolecular distance between the n‐type host and BFD unit enables the implementation of zero‐radius intramolecular energy transfer in the exciplex mechanism. As a result, due to the remarkable improvement in the efficiency and the intermolecular distance‐dependent Förster resonance energy transfer rate, a high efficiency of 15.24% was achieved. Additionally, by modifying the position of the triazine moiety within the molecule, it was possible to maintain a high blue color purity even in high‐doping environments. The concept of BFDs fused with n‐type host molecules departs from the conventional framework of distinguishing between hosts and dopants, presenting a new paradigm in molecular design.