Heteroleptic [Cu(P^P)(N^N)][PF6] complexes, where N^N is 5,5'-dimethyl-2,2'-bipyridine (5,5'-Me2bpy), 4,5,6-trimethyl-2,2'-bipyridine (4,5,6-Me3bpy), 6-(tert-butyl)-2,2'-bipyridine (6-tBubpy) and 2-ethyl-1,10-phenanthroline (2-Etphen) and P^P is either bis(2-(diphenylphosphino)phenyl)ether (POP, PIN [oxydi(2,1-phenylene)]bis(diphenylphosphane)) or 4,5-bis(diphenylphosphino)-9,9-dimethylxanthene (xantphos, PIN (9,9-dimethyl-9H-xanthene-4,5-diyl)bis(diphenylphosphane)) have been synthesized and their NMR spectroscopic, mass spectrometric, structural, electrochemical and photophysical properties were investigated. The single-crystal structures of [Cu(POP)(5,5'-Me2bpy)][PF6], [Cu(xantphos)(5,5'-Me2bpy)][PF6], [Cu(POP)(6-tBubpy)][PF6], [Cu(POP)(4,5,6-Me3bpy)][PF6]·1.5Et2O, [Cu(xantphos)(4,5,6-Me3bpy)][PF6]·2.33CH2Cl2, [Cu(POP)(2-Etphen)][PF6] and [Cu(xantphos)(2-Etphen)][PF6] are described. While alkyl substituents in general exhibit electron-donating properties, variation in the nature and substitution-position of the alkyl group in the N^N chelate leads to different effects in the photophysical properties of the [Cu(P^P)(N^N)][PF6] complexes. In the solid state, the complexes are yellow to green emitters with emission maxima between 518 and 602 nm, and photoluminescence quantum yields (PLQYs) ranging from 1.1 to 58.8%. All complexes show thermally activated delayed fluorescence (TADF). The complexes were employed in the active layer of light-emitting electrochemical cells (LECs). The device performance properties are among the best reported for copper-based LECs, with maximum luminance values of up to 462 cd m-2 and device half-lifetimes of up to 98 hours.

A series of copper(I) complexes of the type [Cu(HN-xantphos)((NN)-N-<^>)][PF6] and [Cu(BnN-xantphos)((NN)-N-<^>)][PF6], in which (NN)-N-<^> = bpy, Mebpy, and Me(2)bpy, HN-xantphos = 4,6-bis(diphenylphosphanyl)-10H-phenoxazine and BnN-xantphos = 10-benzyl-4,6-bis(diphenylphosphanyl)-10H-phenoxazine is described. The single crystal structures of [Cu(HN-xantphos)(Mebpy)][PF6] and [Cu(BnN-xantphos)(Me(2)bpy)][PF6] confirm the presence of (NN)-N-<^> and (PP)-P-<^> chelating ligands with the copper(I) atoms in distorted coordination environments. Solution electrochemical and photophysical properties of the BnN-xantphos-containing compounds (for which the highest-occupied molecular orbital is located on the phenoxazine moiety) are reported. The first oxidation of [Cu(BnN-xantphos)((NN)-N-<^>)][PF6] occurs on the BnN-xantphos ligand. Time-dependent density functional theory (TD-DFT) calculations have been used to analyze the solution absorption spectra of the [Cu(BnN-xantphos)((NN)-N-<^>)][PF6] compounds. In the solid-state, the compounds show photoluminescence in the range 518-555 nm for [Cu(HN-xantphos)((NN)-N-<^>)][PF6] and 520-575 nm for [Cu(BnN-xantphos)((NN)-N-<^>)][PF6] with a blue-shift on going from bpy to Mebpy to Me(2)bpy. [Cu(BnN-xantphos)(Me(2)bpy)][PF6] exhibits a solid-state photoluminescence quantum yield of 55% with an excited state lifetime of 17.4 mu s. Bright light-emitting electrochemical cells are obtained using this complex, and it is shown that the electroluminescence quantum yield can be enhanced by using less conducting hole injection layers.

Using a density functional theory approach, we explore the emission properties of a family of bis-cyclometallated cationic iridium(iii) complexes of general formula [Ir(C^N)2(CN-tert-Bu)2]+ that have tert-butyl isocyanides as neutral auxiliary ligands. Taking the [Ir(ppy)2(CN-tert-Bu)2]+ complex (Hppy = 2-phenylpyridine) as a reference, the effect of replacing the pyridine ring in the cyclometallating ppy ligand by a five-membered azole ring has been examined. To this end, two series of complexes differing by the nature of the atom (either nitrogen or carbon) linking the azole to the phenyl ring of the cyclometallating ligand have been designed. Each series is composed of three molecules having an increasing number of nitrogen atoms (2 to 4) in the azole ring. The emission energies computed for the azole-containing [Ir(C^N)2(CN-tert-Bu)2]+ complexes show a generalized blue-shift compared to [Ir(ppy)2(CN-tert-Bu)2]+, in agreement with the experimental data available for two of the six complexes designed here. The electronic nature of the lowest-lying triplet (T1) is clearly established as a ligand-centred (3LC) state associated with the cyclometallating ligands, and cannot be described as a simple HOMO → LUMO promotion. Therefore, no clear trend based on the sole use of molecular orbital energies can be inferred to predict the emission properties. The significant oscillation in the emission quantum yield (ranging from 0.1% to 52%) experimentally reported is rationalized by the energy gap between the emitting T1 state and a non-radiative triplet state having metal-centred (3MC) d-d* nature. On the basis of such a model, two of the here proposed systems are expected to display significant emission quantum yields in the blue region of the visible spectra, which make them good candidates for electroluminescent applications.

The effects on photo-and electroluminescent properties of structurally modifying the bisphosphane in [Cu(N^N)(P^P)]+complexes (N^N = bpy, 6-Mebpy, 6,6′-Me2bpy) are described.

The synthesis and characterization of five [Cu(P^P)(N^N)][PF6] complexes in which P^P = 2,7-bis(tert-butyl)-4,5-bis(diphenylphosphino)-9,9-dimethylxanthene (tBu2xantphos) or the chiral 4,5-bis(mesitylphenylphosphino)-9,9-dimethylxanthene (xantphosMes2) and N^N = 2,2'-bipyridine (bpy), 6-methyl-2,2'-bipyridine (6-Mebpy) or 6,6'-dimethyl-2,2'-bipyridine (6,6'-Me2bpy) are reported. Single crystal structures of four of the compounds confirm that the copper(i) centre is in a distorted tetrahedral environment. In [Cu(xantphosMes2)(6-Mebpy)][PF6], the 6-Mebpy unit is disordered over two equally populated orientations and this disorder parallels a combination of two dynamic processes which we propose for [Cu(xantphosMes2)(N^N)]+ cations in solution. Density functional theory (DFT) calculations reveal that the energy difference between the two conformers observed in the solid-state structure of [Cu(xantphosMes2)(6-Mebpy)][PF6] differ in energy by only 0.28 kcal mol-1. Upon excitation into the MLCT region (λexc = 365 nm), the [Cu(P^P)(N^N)][PF6] compounds are yellow to orange emitters. Increasing the number of Me groups in the bpy unit shifts the emission to higher energies, and moves the Cu+/Cu2+ oxidation to higher potentials. Photoluminescence quantum yields (PLQYs) of the compounds are low in solution, but in the solid state PLQYs of up to 59% (for [Cu(tBu2xantphos)(6,6'-Me2bpy)]+) are observed. Increased excited-state lifetimes at low temperature are consistent with the complexes exhibiting thermally activated delayed fluorescence (TADF). This is supported by the small energy difference calculated between the lowest-energy singlet and triplet excited states (0.17-0.25 eV). The compounds were tested in simple bilayer light-emitting electrochemical cells (LECs). The optoelectronic performances of complexes containing xantphosMes2 were generally lower with respect to those with tBu2xantphos, which led to bright and efficient devices. The best performing LECs were obtained for the complex [Cu(tBu2xantphos)(6,6'-Me2bpy)][PF6] due to the increased steric hindrance at the N^N ligand, resulting in higher PLQY.

Invited for this month's cover are the research groups of Professors Catherine Housecroft and Edwin Constable from the University of Basel, Switzerland and Professor Enrique Ortí and Dr. Henk Bolink from the University of Valencia, Spain. These groups have a longstanding collaboration to investigate molecular electronic devices, in particular light‐emitting electrochemical cells (LECs) and organic light‐emitting diodes (OLEDs). The featured article highlights the development of LECs with copper(I)‐based emitters for devices consisting of Earth‐abundant materials. Read the full text of the article at 10.1002/cplu.201700501 .

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

LECs with [Ir(tppy)2(btzpy)][PF6] (tppy = 2-(3-(tert-butyl)phenyl)pyridine, btzpy = 2-(pyridine-2-yl)benzo[d]thiazole) in the active layer exhibit pure red emission and are very stable over 5 days of continuous operation.

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.

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)(2)bpy, 6-CF(3)bpy, 5,5-(CF3)(2)bpy, 4,4-(CF3)(2)bpy, 6,6-Me-2-4,4-(CF3)(2)bpy)) 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)(2)bpy}][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)(2)bpy}][PF6] has the highest photoluminescence quantum yield (PLQY; 50.3%) with an emission lifetime of 12s. Compared to 298K solution behavior, excited-state lifetimes became longer in frozen Me-THF (77K; 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 (0.12-0.20eV) permits TADF. Light-emitting electrochemical cells (LECs) with [Cu(POP)+(6-CF(3)bpy)][PF6], [Cu(xantphos)(6-CF(3)bpy)][PF6], or [Cu(xantphos){6,6-Me-2-4,4-(CF3)(2)bpy}][PF6] emit yellow electroluminescence. The LEC with [Cu(xantphos){6,6-Me-2-4,4-(CF3)(2)bpy}][PF6] had the fastest turn-on time (8min), and the LEC with the longest lifetime (t(1/2) = 31 h) contained [Cu(xantphos)(6-CF(3)bpy)][PF6]; these LECs reached maximum luminances of 131 and 109cdm(-2), respectively.

A theoretical density functional theory study has been performed on a family of cationic iridium(III) complexes of the form [Ir((CN)-N-boolean AND)(2)(dtBubpy)](+) (dtBubpy = 4,4'-di-tert-butyl-2,2'-bipyridine), that incorporate 2-phenylpyridine (1, 2) and 1-phenylpyrazole (3, 4) cyclometallating (CN)-N-boolean AND ligands functionalized with SF5 groups. The goal is to investigate the effect that the inclusion of SF5 groups in meta (1, 3) and para position (2, 4) with respect to the Ir-C bond has on the electronic nature of the emitting triplet state and the emission wavelength. The attachment of the electron-withdrawing groups induces the stabilization of the molecular orbitals localized on the (CN)-N-boolean AND ligands and, in particular, of the highest-occupied molecular orbital (HOMO). This stabilization enlarges the energy gap between the HOMO and the lowest-unoccupied molecular orbital (LUMO), and shifts to higher energies the metal-to-ligand charge transfer (MLCT) triplet described by the HOMO -> LUMO excitation. As a consequence, a triplet state of ligand-centered (LC) nature becomes the lowest-energy triplet excited state for all the four complexes. For complexes 1 and 2, the state is centered on the (CN)-N-boolean AND ligands ((LCC boolean AND N)-L-3) and the introduction of the SF5 groups in para causes a greater effect than their insertion in meta. Substitution of the pyridine ring by a pyrazole ring in complexes 3 and 4 destabilizes the (LCc boolean AND N)-L-3 states and the lowest-energy triplet involves the diimine (NN)-N-boolean AND ligand ((LCN boolean AND N)-L-3). Theoretical calculations therefore predict that the electronic nature of the lowest-lying triplet drastically changes in passing from the unsubstituted complex ((MLCT)-M-3) to complexes 1 and 2 ((LCC boolean AND N)-L-3) and to complexes 3 and 4 ((LCN boolean AND N)-L-3). These changes help to rationalize the aspect of the emission spectra and the shift to the blue of the emission wavelength. The appearance of low energy (LC)-L-3 triplets centered on the ancillary ligand, whose energy is hardly affected by changes in the (CN)-N-boolean AND ligands structure, constitutes a limit to blue-shift the phosphorescence emission in this kind of complexes. (C) 2017 Elsevier Ltd. All rights reserved.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

AbstractInvited for this month's cover are the research groups of Professors Catherine Housecroft and Edwin Constable from the University of Basel, Switzerland and Professor Enrique Ortí and Dr. Henk Bolink from the University of Valencia, Spain. These groups have a longstanding collaboration to investigate molecular electronic devices, in particular light‐emitting electrochemical cells (LECs) and organic light‐emitting diodes (OLEDs). The featured article highlights the development of LECs with copper(I)‐based emitters for devices consisting of Earth‐abundant materials. Read the full text of the article at 10.1002/cplu.201700501.

The synthesis and characterization of a series of new cyclometalated iridium(III) complexes [Ir(ppy)2(N∧N)][PF6] in which Hppy = 2-phenylpyridine and N∧N is (pyridin-2-yl)benzo[d]thiazole (L1), 2-(4-(tert-butyl)pyridin-2-yl)benzo[d]thiazole (L2), 2-(6-phenylpyridin-2-yl)benzo[d]thiazole (L3), 2-(4-(tert-butyl)-6-phenylpyridin-2-yl)benzo[d]thiazole (L4), 2,6-bis(benzo[d]thiazol-2-yl)pyridine (L5), 2-(pyridin-2-yl)benzo[d]oxazole (L6), or 2,2'-dibenzo[d]thiazole (L7) are reported. The single crystal structures of [Ir(ppy)2(L1)][PF6]·1.5CH2Cl2, [Ir(ppy)2(L6)][PF6]·CH2Cl2, and [Ir(ppy)2(L7)][PF6] have been determined. The new complexes are efficient red emitters and have been used in the active layers in light-emitting electrochemical cells (LECs). The effects of modifications of the 2-(pyridin-2-yl)benzo[d]thiazole ligand on the photoluminescence and LEC performance have been examined. Extremely stable red-emitting LECs are obtained, and when [Ir(ppy)2(L1)][PF6], [Ir(ppy)2(L2)][PF6], or [Ir(ppy)2(L3)][PF6] are used in the active layer, device lifetimes greater than 1000, 6000, and 4000 h, respectively, are observed.

A series of bis-cyclometalated iridium(III) complexes of general formula [Ir(ppy)2(N∧N)][PF6] (ppy- = 2-phenylpyridinate; N∧N = 2-(1H-imidazol-2-yl)pyridine (1), 2-(2-pyridyl)benzimidazole (2), 1-methyl-2-pyridin-2-yl-1H-benzimidazole (3), 2-(4'-thiazolyl)benzimidazole (4), 1-methyl-2-(4'-thiazolyl)benzimidazole (5)) is reported, and their use as electroluminescent materials in light-emitting electrochemical cell (LEC) devices is investigated. [2][PF6] and [3][PF6] are orange emitters with intense unstructured emission around 590 nm in acetonitrile solution. [1][PF6], [4][PF6], and [5][PF6] are green weak emitters with structured emission bands peaking around 500 nm. The different photophysical properties are due to the effect that the chemical structure of the ancillary ligand has on the nature of the emitting triplet state. Whereas the benzimidazole unit stabilizes the LUMO and gives rise to a 3MLCT/3LLCT emitting triplet in [2][PF6] and [3][PF6], the presence of the thiazolyl ring produces the opposite effect in [4][PF6] and [5][PF6] and the emitting state has a predominant 3LC character. Complexes with 3MLCT/3LLCT emitting triplets give rise to LEC devices with luminance values 1 order higher than those of complexes with 3LC emitting states. Protecting the imidazole N-H bond with a methyl group, as in complexes [3][PF6] and [5][PF6], shows that the emissive properties become more stable. [3][PF6] leads to outstanding LECs with simultaneously high luminance (904 cd m-2), efficiency (9.15 cd A-1), and stability (lifetime over 2500 h).

Water has a great tendency to associate through hydrogen bonding with water molecules or other hydrogen bond donor or acceptor groups. Here the case of a water molecule encapsulated in the interior of a metallocage receptor is presented. The association of four copper(II) ions and two aza-macrocyclic receptors in which two 1H-pyrazole units are connected by cadaverine diamines leads to the inclusion of a water molecule into the cage, as proved by X-ray analysis and infrared spectroscopy. The included water molecule shows no hydrogen bonding with any component of the cage presenting only a weak hydrogen bond with an oxygen atom of a perchlorate counter-anion. The IR stretching vibrations predicted by DFT calculations agree with the experimental results.