Bright green-to-yellow emitting Cu(i) complexes based on bis(2-pyridyl)phosphine oxides: synthesis, structure and effective thermally activated-delayed fluorescence

Abstract

A family of brightly luminescent dinuclear complexes of [Cu(μ-X)(N^N)] type (X = I or SCN) has been synthesized in 76-90% yields by the reaction of bis(2-pyridyl)phosphine oxides (N^N) with the corresponding Cu(i) salts. The X-ray diffraction study reveals that the CuI core of the [Cu(μ-I)(N^N)] complexes has either a butterfly- or rhomboid-shaped structure, while the eighth-membered [Cu()Cu] ring in the [Cu(SCN)(N^N)] complexes is nearly planar. In the solid state, these compounds exhibit a strong green-to-yellow emission (λ = 536-592 nm) with high PLQYs (up to 63%) and short lifetimes (1.9-10.0 μs). The combined photophysical and DFT study indicates that the ambient-temperature emission of the complexes obtained can be assigned to the thermally activated-delayed fluorescence (TADF) from the (M + X)LCT excited state, while at 77 K, phosphorescence from the(M + X)LCT state is likely observed.

Synthesis, Structure, and Photophysical Properties of Yellow-Green and Blue Photoluminescent Dinuclear and Octanuclear Copper(I) Iodide Complexes with a Disilanylene-Bridged Bispyridine Ligand

“…Although most Cu(I) complexes with chelating pyridine-based ligands showed weak emission from the MLLCT excited state with low quantum yield, dicopper complex 2 showed broad and non-structured yellow-green (519 nm) emission in the solid state in good photoluminescent intensity (Φ = 0.60, Figure 2) [54]. The luminescence wavelength and quantum yield of 2 are in a normal range of the dicopper(I) iodide complexes with a rhombic core, which rationalizes the initial molecular design [55,56]. Complex 3 also shows broad and nonstructured blue emission (478 nm, Φ = 0.04) in the solid state.…”

Oligophosphine-thiocyanate Copper(I) and Silver(I) Complexes and Their Borane Derivatives Showing Delayed Fluorescence

“…In all these complexes except 2 , the thiocyanate ligands are coordinated in a μ 2 ,κ 2 -mode and bridge two metal centers to give the MM metallacycles, which have been previously observed for the related copper(I) and silver(I) species. 38−44 A copper complex that is nearly identical to 5 , having a diphosphine ligand with o -tolyl substituents on one phosphorus center, has been structurally characterized earlier. 45 The diphosphine ligands complete the distorted tetrahedral geometry of each metal ion and are bound to the MM motifs in a trans -manner in centrosymmetric molecules of 1 and 4 – 6 .…”

“…In general, the values of bond lengths and angles determined for 1 – 6 (Table S2) are typical for this sort of complex and correlate well with the reported data. 38−44,46…”

TADF: Enabling luminescent copper(i) coordination compounds for light-emitting electrochemical cells

“…Most of these are neutral and are of interest for OLEDs; selected examples which have been tested in OLED configurations are shown in Scheme 3. 36,64–96…”