Journal Article

Through‐space interaction enables simultaneous enhancements of kr and kRISC in highly efficient spiro‐acridine based thermally activated delayed fluorescence emitter with acridone acceptor

Wang, Jiahui, Mei, Yongqiang, Xu, Min, Wan, Huihui, Jin, Jing, Liu, Di, Xie, Lijuan, Li, Jiuyan

2025

Overview

Most of acridine based thermally activated delayed fluorescence (TADF) emitters are characterized by advantageous reverse intersystem crossing (RISC) rate (kRISCs) due to the perpendicular orientation of the acridine donor to the acceptor moiety, but suffer from a poor radiation rate (kr) typically in the order of 106 s−1. Herein, two sky blue TADF emitters 3,6‐DMAC‐AD‐Py and 3,6‐SFAC‐AD‐Py were developed by linking acridine (DMAC) and spiro‐fluorene‐acridine (SFAC) donors to 10‐(pyridin‐2‐yl)acridin‐9(10H)‐one (AD‐Py) acceptor. Larger SFAC and electron‐deficient pyridyl groups are deliberately incorporated in 3,6‐SFAC‐AD‐Py since the unique through‐space interaction between them is designed to drive the rotation of inner acridine ring in SFAC for enhancing frontier molecular orbitals overlap while keeping a decent TADF behavior. Thus, the kr of 3,6‐SFAC‐AD‐Py is increased to 1.5 × 107 s−1. Simultaneously, SFAC donors improve spin orbital coupling strength and reduce the energy gaps, generating kRISC of 1.8 × 106 s−1. This is the first acridine donor based TADF emitter realizing kr of 107 s−1 and kRISC of 106 s−1 by a through‐space interaction strategy. 3,6‐SFAC‐AD‐Py enables a highly efficient sky‐blue organic light‐emitting diode with a maximum external quantum efficiency (EQE) of 34.7% and Commission International de I'Eclairage coordinates of (0.19, 0.37). More importantly, the EQE still remained 27.6% and 16.9% at high brightness of 1000 and 10,000 cd m−2. Intramolecular through‐space interaction is designed for the first time in a thermally activated delayed fluorescence emitter to pull the appropriate rotation of the acridine donor to deviate from the perpendicular orientation, which solves the common problem of insufficient FMO overlap to simultaneously enhance the radiation transition and reverse intersystem crossing process and thus lead to a high EQE of 34.7% with quite slow efficiency roll‐off in blue organic light‐emitting diodes.

• Publisher: Wiley
• Subject: acridine donor / intramolecular through‐space interaction / low efficiency roll‐off / radiative rate constant / reverse intersystem crossing (RISC) / thermally activated delayed fluorescence (TADF)