Copper(I) TADF exciplexes via Metal-Perturbed Through-Space charge transfer for efficient OLEDs

Abstract

Organo-copper(I) emitters are promising cost-effective candidates as triplet-harvesting dopants in organic light-emitting diodes (OLEDs). To date, the mainstream design of Cu(I) emitters depends on ligand engineering to modify intramolecular charge transfer and thus modulate the related optoelectronic properties. However, little is known on luminescent Cu(I) systems based on intermolecular charge transfer. For the first time, the proof-of-concept Cu(I) exciplexes were developed employing a triazine-containing molecule DMIC-TRZ as an acceptor and several Cu(I)-based carbene-metal-amide (CMA) complexes as donors. The formation of these exciplexes is strongly associated with d-orbital participation of Cu atom on the highest occupied molecular orbital of CMA complexes to match with the acceptor DMIC-TRZ. These Cu(I) exciplexes not only displayed donor-dependent emission colors spanning from sky blue to red but also exhibited distinct thermally activated delayed fluorescence (TADF) via copper(I)-perturbed through-space charge transfer (TSCT). The OLEDs adopting the Cu(I) exciplexes as emitters delivered good external quantum efficiency (EQE) of up to 10.9%. Furthermore, the use of these Cu(I) exciplexes as hosts for multi-resonance TADF emitters delivered narrowband electroluminescence with high EQEs of up to 24.9%, superior to the reference OLEDs based on the common host.