Four highly efficient cuprous complexes and their applications in solution-processed organic light-emitting diodes

Abstract

Four mononuclear cationic Cu(I) complexes featuring functional C-linked pyrazolyl pyridine diimine ligands have been synthesized and characterized. Under UV 365 nm at room temperature, these complexes emit similar orange light in solution and green light in thin film, which could be attributed to the limited charge and steric influence of these methyl or trifluoromethyl substituted phenyl appendages at the pyrazol ring.Moreover, multilayer organic light-emitting diodes (OLEDs) based on these Cu(I) complexes had different performance efficiencies. The device with complex 1 as the light emitting material had the highest current efficiency of 17.8 cd A À1 and an external quantum efficiency (EQE) of 6.4%, while the device with complex 2 which shows the highest photoluminescence quantum yields gave the poorest device efficiency with a current efficiency of 13 cd A À1 and an EQE of 4.7%.

Synthesis, Structure, and Characterization of Emissive Neutral Dinuclear CuI Complexes with a Tetraphosphane Bridging Ligand

“…These non‐bonding intramolecular distances of Cu ··· Cu are much longer than those in the binuclear copper complexes with halide anions as bridging ligands, [(L)Cu(µ‐X) 2 Cu(L)] (L = bidentate chelating ligands of P and N). [3j], [3k], …”

“…Cuprous emissive complexes have been investigated intensively since 1980, and have become an important class of luminescent materials . Except for a few examples of three‐coordinated emissive Cu I complexes, the majority of Cu I luminescent complexes have a distorted tetrahedral geometry around the Cu I atoms defined by two diimine ligands ([Cu(NN) 2 + ]) or a diimine ligand and a diphosphane ligand ([Cu(NN)(PP) + ]) . Compared with the homoleptic [Cu(NN) 2 + ] complexes, mixed‐ligand complexes [Cu(NN)(PP) + ] with phosphane ligands exhibit improved emissions owing to the electron‐withdrawing effect of the P ligands .…”

Cu(I) complexes – Thermally activated delayed fluorescence. Photophysical approach and material design

“…This did not only lead to a much deeper understanding of photophysical and chemical properties of the Cu(I) compounds, but led also to the development of an enormous number of new materials with strongly improved properties, for example, with respect to an application as OLED emitters. [5,[27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43] Moreover, material design strategies could be developed for engineering of highly efficient emitters and even new emission mechanisms could be proposed [44,45].…”

TADF Material Design: Photophysical Background and Case Studies Focusing on CuIand AgIComplexes

“…This became particularly apparent for classes of compounds that may be applied as emitters in organic light emitting diodes (OLEDs) or in light emitting electrochemical cells (LEEC) . These scientific investigations led to a much deeper understanding of photophysical principles and of the compound's properties resulting in the development of an enormous number of new materials in part with drastically improved properties for OLED applications . Improvements were also stimulated in the fields of related functional materials based on metal complexes for sensing of oxygen or temperature or for photocatalysis …”

“…Hence, as a rule of thumb, efficient thermal activation with fast up‐ISC or reverse ISC (=RISC) is not expected to occur for Δ E (S 1 –T 1 ) distinctly above 10 3 cm −1 (≈130 meV). Indeed, such energy separations can be realized with environmentally friendly and low‐cost Cu I and Ag I[104, 106–109] complexes as well as with purely organic molecules …”