Efficient Blue Photo- and Electroluminescence from CF3-Decorated Cu(I) Complexes.

Luminescent organometallic complexes of earth-abundant copper(I) have long been studied in organic light-emitting diodes (OLED). Particularly, Cu(I)-based carbene-metal-amide (CMA) complexes have recently emerged as promising organometallic emitters. However, blue-emitting Cu(I) CMA complexes have been rarely reported. Here we constructed two blue-emitting Cu(I) CMA emitters, MAC*-Cu-CF3Cz and MAC*-Cu-2CF3Cz, by introducing one or two CF3 substitutes into carbazole ligands. Both complexes exhibited high thermal stability and blue emission colors. Moreover, two complexes exhibited different emission origins rooting from different donor ligands: a distinct thermally activated delayed fluorescence (TADF) from ligand-to-ligand charge transfer excited states for MAC*-Cu-CF3Cz or a dominant phosphorescence nature from local triplet excited state of the carbazole ligand for MAC*-Cu-2CF3Cz. Inspiringly, MAC*-Cu-CF3Cz had high photoluminescence quantum yields of up to 94 % and short emission lifetimes of down to 1.2 µs in doped films, accompanied by relatively high radiative rates in the 105 s-1 order. The resultant vacuum-deposited OLEDs based on MAC*-Cu-CF3Cz delivered pure-blue electroluminescence at 462 nm together with a high external quantum efficiency of 13.0 %.

Aggregation-Dependent Circularly Polarized Luminescence and Thermally Activated Delayed Fluorescence from Chiral Carbene-CuI -Amide Enantiomers.

The field of luminescent carbene-metal-amide (CMA) complexes and chiroptical-active materials has been blossoming in recent years, although chiroptical-active CMA complexes have not been reported so far. For the first time, a pair of chiral CuI -based CMA enantiomers, (R,R)-PSIPr*-Cu-DMAC and (S,S)-PSIPr*-Cu-DMAC, have been developed by using chiral phenyl-substituted N-heterocyclic carbenes as acceptor ligands in the CMA motif. The CuI -based CMA enantiomers exhibited aggregation-induced circularly polarized luminescence with a large luminescence dissymmetry factor of up to +0.027, the first reported for CMA complexes. This success originates from the limited ligand-ligand rotation freedom and asymmetrical packing pattern (helical structure) of the CMA enantiomers in the crystals. Moreover, these CuI enantiomers displayed inspiring aggregation-dependent thermally activated delayed fluorescence properties. These findings bring new insights into the optical properties of chiral CMA complexes from the perspective of aggregation states.