Efficient Color-Tunable Copper(I) Complexes and Their Applications in Solution-Processed Organic Light-Emitting...

A series of dppnc- and neocuproine-based Cu^I complexes (dppnc=7,8-bis(diphenylphosphino)-7,8-dicarba-nido-undecaborate) are synthesized and the emission color of these Cu^I complexes can be tuned from green to deep red via rational modification of the neocuproine ligand structure. The molecular structures of the emissive Cu^I complexes, Cu(dppnc)-G (green emitting), Cu(dppnc)-Y (yellow emitting), and Cu(dppnc)-R (red emitting), are characterized and their electronic structures and related transition properties are elucidated by photo-physical and computational (density functional theory) studies. The calculation results suggest that thermally activated delayed fluorescence (TADF) is the emission mechanism for these Cu^I complexes. Efficient solution-processed green-, yellow-, and red-emitting OLEDs are fabricated based on the emissive complexes as the dopants. High external quantum efficiency (EQE) of 15.20 % and current efficiency of 48.15 cd A^-1 at 1000 cd m^-2 are achieved in the green-emitting device with Cu(dppnc)-G. A maximum EQE of 10.17 %, CIE coordinates of (0.61, 0.38) and a maximum electroluminescent peak of 631 nm are achieved in the red device based on Cu(dppnc)-R.