Copper-based LECs with a maximum efficacy of 3.0 cd A−1 (luminance = 145 cd m−2) or with lifetimes >80 h have been achieved.

Light-emitting electrochemical cells (LECs) containing [Cu(POP)(N^N)][PF6] (POP = bis(2-diphenylphosphinophenyl)ether, N^N = 6-methyl- or 6,6'-dimethyl-2,2'-bipyridine) exhibit luminance and efficiency surpassing previous copper(I)-containing LECs.

Herein, [Cu(P^P)(N^N)][PF6] complexes (P^P=bis[2‐(diphenylphosphino)phenyl]ether (POP) or 4,5‐bis(diphenylphosphino)‐9,9‐dimethylxanthene (xantphos); N^N=CF3‐substituted 2,2′‐bipyridines (6,6′‐(CF3)2bpy, 6‐CF3bpy, 5,5′‐(CF3)2bpy, 4,4′‐(CF3)2bpy, 6,6′‐Me2‐4,4′‐(CF3)2bpy)) are reported. The effects of CF3 substitution on their structure as well as their electrochemical and photophysical properties are also presented. The HOMO–LUMO gap was tuned by the N^N ligand; the largest redshift in the metal‐to‐ligand charge transfer (MLCT) band was for [Cu(P^P){5,5′‐(CF3)2bpy}][PF6]. In solution, the compounds are weak yellow to red emitters. The emission properties depend on the substitution pattern, but this cannot be explained by simple electronic arguments. Among powders, [Cu(xantphos){4,4′‐(CF3)2bpy}][PF6] has the highest photoluminescence quantum yield (PLQY; 50.3 %) with an emission lifetime of 12 μs. Compared to 298 K solution behavior, excited‐state lifetimes became longer in frozen Me‐THF (77 K; THF=tetrahydrofuran), thus indicating thermally activated delayed fluorescence (TADF). Time‐dependent (TD)‐DFT calculations show that the energy gap between the lowest‐energy singlet and triplet excited states (0.12–0.20 eV) permits TADF. Light‐emitting electrochemical cells (LECs) with [Cu(POP)+(6‐CF3bpy)][PF6], [Cu(xantphos)(6‐CF3bpy)][PF6], or [Cu(xantphos){6,6′‐Me2‐4,4′‐(CF3)2bpy}][PF6] emit yellow electroluminescence. The LEC with [Cu(xantphos){6,6′‐Me2‐4,4′‐(CF3)2bpy}][PF6] had the fastest turn‐on time (8 min), and the LEC with the longest lifetime (t1/2=31 h) contained [Cu(xantphos)(6‐CF3bpy)][PF6]; these LECs reached maximum luminances of 131 and 109 cd m−2, respectively.

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In a new oxidative route, Ag(+)[Al(OR(F))(4)](-) (R(F)=C(CF(3))(3)) and metallic indium were sonicated in aromatic solvents, such as fluorobenzene (PhF), to give a precipitate of silver metal and highly soluble [In(PhF)(n)](+) salts (n=2, 3) with the weakly coordinating [Al(OR(F))(4)](-) anion in quantitative yield. The In(+) salt and the known analogous Ga(+)[Al(OR(F))(4)](-) were used to synthesize a series of homoleptic PR(3) phosphane complexes [M(PR(3))(n)](+), that is, the weakly PPh(3)-bridged [(Ph(3)P)(3)In-(PPh(3))-In(PPh(3))(3)](2+) that essentially contains two independent [In(PPh(3))(3)](+) cations or, with increasing bulk of the phosphane, the carbene-analogous [M(PtBu(3))(2)](+) (M=Ga, In) cations. The M(I)-P distances are 27 to 29 pm longer for indium, and thus considerably longer than the difference between their tabulated radii (18 pm). The structure, formation, and frontier orbitals of these complexes were investigated by calculations at the BP86/SV(P), B3LYP/def2-TZVPP, MP2/def2-TZVPP, and SCS-MP2/def2-TZVPP levels.

Ga,In insights: A general explanation for the unusual tilted coordination mode of undisturbed gallium(I) and indium(I) carbene complexes of the weakly coordinating anion [Al(ORF)4]− (RF=C(CF3)3) is given, which is based on the experimental structures. The results are supported by extensive DFT studies.

Heteroleptic [Cu(P^P)(N^N)][PF6] complexes, where N^N is a halo-substituted 2,2'-bipyridine (bpy) and P^P is either bis(2-(diphenylphosphino)phenyl)ether (POP) or 4,5-bis(diphenylphosphino)-9,9-dimethylxanthene (xantphos) have been synthesized and investigated. To stabilize the tetrahedral geometry of the copper(i) complexes, the steric demands of the bpy ligands have been increased by introducing 6- or 6,6'-halo-substituents in 6,6'-dichloro-2,2'-bipyridine (6,6'-Cl2bpy), 6-bromo-2,2'-bipyridine (6-Brbpy) and 6,6'-dibromo-2,2'-bipyridine (6,6'-Br2bpy). The solid-state structures of [Cu(POP)(6,6'-Cl2bpy)][PF6], [Cu(xantphos)(6,6'-Cl2bpy)][PF6]·CH2Cl2, [Cu(POP)(6-Brbpy)][PF6] and [Cu(xantphos)(6-Brbpy)][PF6]·0.7Et2O obtained from single crystal X-ray diffraction are described including the pressure dependence of the structure of [Cu(POP)(6-Brbpy)][PF6]. The copper(i) complexes with either POP or xantphos and 6,6'-Cl2bpy, 6-Brbpy and 6,6'-Br2bpy are orange-to-red emitters in solution and yellow-to-orange emitters in the solid state, and their electrochemical and photophysical properties have been evaluated with the help of density functional theory (DFT) calculations. The emission properties are strongly influenced by the substitution pattern that largely affects the geometry of the emitting triplet state. [Cu(POP)(6,6'-Cl2bpy)][PF6] and [Cu(xantphos)(6,6'-Cl2bpy)][PF6] show photoluminescence quantum yields of 15 and 17%, respectively, in the solid state, and these compounds were tested as luminophores in light-emitting electrochemical cells (LECs). The devices exhibit orange electroluminescence and very short turn-on times (<5 to 12 s). Maximum luminance values of 121 and 259 cd m-2 for [Cu(POP)(6,6'-Cl2bpy)][PF6] and [Cu(xantphos)(6,6'-Cl2bpy)][PF6], respectively, were achieved at an average current density of 100 A m-2. External quantum efficiencies of 1.2% were recorded for both complexes.

Bright and stable LECs with [Cu(P^P)(N^N)][PF6] complexes containing 6-alkoxy- or 6-phenyloxy-2,2′-bipyridine ligands.