Highly efficient and stable thermally activated delayed fluorescent palladium(II) complexes for organic light-emitting diodes
Jiangong Yang, Xingyu Feng, Nengquan Li, Jiayu Li, Xiu‐Fang Song, Ming‐De Li, Ganglong Cui, Jingling Zhang, Chenglin Jiang, Chuluo Yang, Kai Li
Abstract
Transition metal complexes exhibiting thermally activated delayed fluorescence (TADF) remain underdeveloped for organic light-emitting diodes (OLEDs). Here, we describe a design of TADF Pd(II) complexes featuring metal-perturbed intraligand charge-transfer excited states. Two orange- and red-emitting complexes with efficiencies of 82 and 89% and lifetimes of 2.19 and 0.97 μs have been developed. Combined transient spectroscopic and theoretical studies on one complex reveal a metal-perturbed fast intersystem crossing process. OLEDs using the Pd(II) complexes show maximum external quantum efficiencies of 27.5 to 31.4% and small roll-offs down to 1% at 1000 cd m −2 . Moreover, the Pd(II) complexes show exceptional operational stability with LT 95 values over 220 hours at 1000 cd m −2 , benefiting from the use of strong σ-donating ligands and the presence of multiple intramolecular noncovalent interactions beside their short emission lifetimes. This study demonstrates a promising approach for developing efficient and robust luminescent complexes without using the third-row transition metals.