Highly Efficient Cuprous Complexes with Thermally Activated Delayed Fluorescence for Solution-Processed Organic Light-Emitting Devices

Abstract

Two mononuclear cuprous complexes [Cu(PNNA)(POP)]BF4 (1) and [Cu(PNNA)(Xantphos)]BF4 (2) (PNNA = 9,9-dimethyl-10-(6-(3-phenyl-1H-pyrazol-1-yl)pyridin-3-yl)-9,10-dihydroacridine, POP = bis[2-(dipenylphosphino)phenyl]ether, Xantphos =4,5-bis(diphenylphosphino)-9,9-dimethylxanthene), with intense bluish-green luminescence based on a new diimine ligand were designed and synthesized. Their structural, electrochemical, and photophysical properties were characterized by single-crystal X-ray analysis, cyclic voltammetry, temperature dependence of spectroscopy, time-dependent emission spectroscopy, etc. The complexes exhibit high photoluminescence quantum yields in doped films (up to 74.6%) at room temperature. Thermally activated delayed fluorescence based on intraligand charge transfer was observed by grafting a strong electron-donor moiety, 9,9-dimethylacridan, on the diimine ligand, which is supported by the density functional theory calculations on two complexes. Highly efficient solution-processed OLEDs based on these two complexes were fabricated, among which the electroluminescent device using 2 as dopant shows a peak external quantum efficiency of 7.42%, a peak current efficiency of 20.24 cd/A, and a maximum brightness of 5579 cd/m(2).

Synthesis, Structures, and Photophysical Properties of Novel Four-Coordinate Cu(I) Complexes Supported by Chelating N-Heterocyclic Carbene Ligands

“…It is interesting that the Cu–C bond lengths show an opposite trend to Cu–N bond lengths. The average Cu–P bond lengths fall in the range 2.2505 −2.2712 Å, which are similar to those of reported four-coordinate Cu(I)complexes (Kuang et al, 2002; Gneuß et al, 2015; Liang et al, 2016; Brunner et al, 2017, 2019; Huang et al, 2017; Zhang et al, 2017; Alkan-Zambada et al, 2018; Keller et al, 2018). The dihedral angles between the imidazolylidene rings and pyrimidine rings in NHC ligands are 5.5(5) o , 15.5(4) o , 17.3(3) o , 5.1(4) o , and 9.2(6) o for [Cu(Pmim)(POP)](PF 6 ), [Cu(Cl-Pmim)(POP)](PF 6 ), [Cu(F-Pmim)(POP)](PF 6 ), [Cu(Me-Pmim)(POP)](PF 6 ) and [Cu(MeO-Pmim)(POP)](PF 6 ), respectively.…”

“…For example, the photoluminescence quantum yield (ϕ PL ) of [Cu(dbp)(POP)] + is hundreds-fold larger than those of [Cu(N ∧ N) 2 ] + , where POP = bis[2-(diphenylphosphino)phenyl]ether, dbp = 2,9-di- n -butyl-1,10-phenanthroline. In recent years, lots of luminescent heteroleptic Cu(I) complexes supported by chelating diphosphine ligands and diimine ligands (general formula [Cu(P ∧ P)(N ∧ N)] + ) have been successfully developed, and efficient EL devices based on this kind of Cu(I) complexes have been fabricated (Cheng et al, 2015; Osawa et al, 2015; Liang et al, 2016; Lin et al, 2017; Zhang et al, 2017; Alkan-Zambada et al, 2018; Keller et al, 2018; Liu et al, 2018; Brunner et al, 2019).…”

Syntheses, Crystal Structures and Photophysical Properties of Dinuclear Copper(I) Complexes Bearing Diphenylphosphino‐Substituted Benzimidazole Ligands

“…No emission from mCP and TCTA are observed, implying that energy transfer is sufficient from host material to Cu(I) dimers. The turn‐on voltages (V on ) of the devices are 5.2 V for A , 5.2 V for B , and 7.3 V for C (Table S10), which are comparable to those of previously report OLEDs based on Cu(I) complexes [23b,25b] . Notably, the maximum current efficiencies (CE max ) of A are 8.22 cd A −1 , which is higher than that of B (3.27 cd A −1 ), and C (3.97 cd A −1 ), respectively.…”

Eliminating nonradiative decay in Cu(I) emitters: >99% quantum efficiency and microsecond lifetime

“…4B), consistent with the high triplet energy of the UGH3 host (T 1 = 3.5 eV). Although the EQE values for greenand yellow-or orange-emitting Cu-based OLEDs have been reported to be >20% (42,43), the highest efficiencies previously reported for blueemitting (EL l max < 500 nm) Cu-based OLEDs are <6% (44,45). The low EQE max of the mCBP and mCP devices can be explained by a low triplet energy for the hosts (mCBP, T 1 = 2.8 eV; mCP, T 1 = 2.9 eV), which do not confine triplet excitons on the Cu emitter as efficiently as UGH3.…”