Strongly yellow photo- and electroluminescent palladium(ii) complexes via metal-assisted thermally activated delayed fluorescence

Abstract

Two luminescent palladium(II) complexes, namely PdBO and DPdBO, featuring metal-perturbed intraligand charge transfer (MPICT) excited states have been designed and synthesized. Single-crystal X-ray structures of both complexes indicate the presence of intramolecular multiple noncovalent interactions including metal⋯π, π⋯π and C–H⋯π interactions. Both complexes have good thermal stability with decomposition temperatures of 384 and 435 °C, presumably benefitting from the assistance of noncovalent interactions. Photophysical studies of both complexes reveal efficient yellow thermally activated delayed fluorescence (TADF) with photoluminescence quantum yields of 91% and 89%, respectively. Organic light-emitting diodes (OLEDs) based on PdBO show a maximum external quantum efficiency (EQE) of 19.5%. This work shows the facile design of TADF Pd(II) complexes based on the MPICT strategy which features a non-coordinating electron-acceptor moiety.