The archetype ionic transition‐metal complexes (iTMCs) [Ir(ppy)2(bpy)][PF6] and [Ir(ppy)2(phen)][PF6], where Hppy = 2‐phenylpyridine, bpy = 2,2′‐bipyridine, and phen = 1,10‐phenanthroline, are used as the primary active components in light‐emitting electrochemical cells (LECs). Solution and solid‐state photophysical properties are reported for both complexes and are interpreted with the help of density functional theory calculations. LEC devices based on these archetype complexes exhibit long turn‐on times (70 and 160 h, respectively) and low external quantum efficiencies (∼2%) when the complex is used as a pure film. The long turn‐on times are attributed to the low mobility of the counterions. The performance of the devices dramatically improves when small amounts of ionic liquids (ILs) are added to the Ir‐iTMC: the turn‐on time improves drastically (from hours to minutes) and the device current and power efficiency increase by almost one order of magnitude. However, the improvement of the turn‐on time is unfortunately accompanied by a decrease in the stability of the device from 700 h to a few hours. After a careful study of the Ir‐iTMC:IL molar ratios, an optimum between turn‐on time and stability is found at a ratio of 4:1. The performance of the optimized devices using these rather simple complexes is among the best reported to date. This holds great promise for devices that use specially‐designed iTMCs and demonstrates the prospect for LECs as low‐cost light sources.

Light‐emitting electrochemical cells with lifetimes surpassing 3000 hours at an average luminance of 200 cd m−2 are obtained with an ionic iridium(III) complex conveniently designed to form a supramolecularly caged structure.

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Three new heteroleptic iridium complexes that combine two approaches, one leading to a high stability and the other yielding a high luminescence efficiency, are presented. All complexes contain a phenyl group at the 6‐position of the neutral bpy ligand, which holds an additional, increasingly bulky substituent on the 4‐position. The phenyl group allows for intramolecular π–π stacking, which renders the complex more stable and yields long‐living light‐emitting electrochemical cells (LECs). The additional substituent increases the intersite distance between the cations in the film, reducing the quenching of the excitons, and should improve the efficiency of the LECs. Density functional theory calculations indicate that the three complexes have the desired π–π intramolecular interactions between the pendant phenyl ring of the bpy ligand and the phenyl ring of one of the ppy ligands in the ground and the excited states. The photoluminescence quantum efficiency of concentrated films of the complexes improves with the increasing size of the bulky groups indicating that the adopted strategy for improving the efficiency is successful. Indeed, LEC devices employing these complexes as the primary active component show shorter turn‐on times, higher efficiencies and luminances, and, surprisingly, also demonstrate longer device stabilities.

The complex [Ir(ppy) 2 (dpbpy)] [PF 6 ] (Hppy = 2-phenylpyridine, dpbpy = 6,6 0 -diphenyl-2,2 0 -bipyridine) has been prepared and evaluated as an electroluminescent component for light-emitting electrochemical cells (LECs); the complex exhibits two intramolecular face-to-face p-stacking interactions and long-lived LECs have been constructed; the device characteristics are not significantly improved in comparison to analogous LECs with 6-phenyl-2,2 0 -bipyridine.Light-emitting electrochemical cells (LECs) are a minimalist derivative of organic light-emitting devices (OLEDs) and in their simplest form consist of a film of an ionic transition metal complex placed between two electrodes. 1,2 LECs offer considerable technological advantages over OLEDs as they require a less reactive cathode material (Al instead of Ca or Mg) because the device is no longer dependent upon the work function of the electrode and hence do not require stringent protection from environmental oxygen or water. The disadvantage of LECs is the short operating lifetime, in the order of hours to days, compared to OLEDs. [3][4][5] We have recently reported the use of intra-and intermolecular face-to-face p-stacking for the stabilisation of the ground and excited state of electroluminescent iridium complexes and shown that this leads to exceptionally long-living LEC devices. 6,7 The long lifetimes of these devices establish LECs as a viable alternative to OLED technology. In [Ir(ppy)(pbpy)] + (Hppy = 2-phenylpyridine, pbpy = 6-phenyl-2,2 0 -bipyridine) the pendant phenyl group of the pbpy ligand forms a face-to-face p-stack with the metallated ring of a ppy ligand (3.2-3.5 Å ). This interaction minimises the expansion of the metal-ligand bonds in the excited state and precludes the attack by water and other nucleophiles resulting in the long observed lifetimes. We concluded that analogous complexes with 6,6 0 -diphenyl-2,2 0 -bipyridine would have an even greater stabilisation of the excited state as the two pendant phenyl groups would stack with different ppy ligands giving a very ''tight'' complex.The ligand 6,60 -diphenyl-2,2 0 -bipyridine, dpbpy, was obtained from the reaction of four equivalents of phenyllithium with 2,2 0 -bipyridine in THF followed by oxidation of the intermediate tetrahydro-species with MnO 2 according to the general procedure of Sauvage et al. ) and the complex is luminescent exhibiting an emission in MeCN solution with a maximum at 595 nm with a lifetime t = 0.6 ms and a quantum yield (PLQE) of 3%.We have determined the structure of [Ir(ppy) 2 (dpbpy)][PF 6 ]z and the [Ir(ppy) 2 (dpbpy)] + cation present in the lattice is shown in Fig. 1a. The Ir-N(ppy) (2.0504(17), 2.0341(17) Å ) and Ir-C(ppy) distances (2.0120 (18) . We stress here that the intramolecular p-stacking is a direct and inevitable consequence of the ligand structure and will be present in the solid state, solution and thin film phases. To summarise, as observed from the crystal structure, the use of the dpbpy ligand for optimising the

A new iridium(III) complex showing intramolecular interligand pi-stacking has been synthesized and used to improve the stability of single-component, solid-state light-emitting electrochemical cell (LEC) devices. The pi-stacking results in the formation of a very stable supramolecularly caged complex. LECs using this complex show extraordinary stabilities (estimated lifetime of 600 h) and luminance values (average luminance of 230 cd m-2) indicating the path toward stable ionic complexes for use in LECs reaching stabilities required for practical applications.

Light-emitting electrochemical cells (LECs) based on ionic transition-metal complexes (iTMCs) exhibiting high effi ciency, short turn-on time, and long stability have recently been presented. Furthermore, LECs emitting in the full range of the visible spectrum including white light have been reported. However, all these achievements were obtained individually, not simultaneously, using in each case a different iTMC. In this work, device stability is maintained by employing intrinsically stable ionic iridium complexes, while increasing the complex and the device quantum yields for exciton-to-photon conversion. This is done by sequentially modifying the archetype ionic iridium complex [Ir(ppy) 2 (bpy)][PF 6 ], where Hppy is 2-phenylpyridine and bpy is 2,2'-bipyridine, with methyl and phenyl groups on the bpy ligand. A full photophysical and theoretical description of a series of four complexes, including the archetype as a reference, is presented and their performance in LECs is characterized. Upon selecting suitable substituents, a twofold increase is obtained in the photoluminescence quantum yield in a solid fi lm. This is refl ected in a significant increase in the effi ciency over time curve for LECs using this complex.

A novel iridium(III) complex, [Ir(dmppz)(2)pbpy][PF(6)] (Hdmppz = 3,5-dimethyl-1-phenylpyrazole and pbpy = 6-phenyl-(2,2'-bipyridine)), is reported. The complex shows an intramolecular face-to-face pi-stacking between the phenyl ring of the dmppz ligand and the pendant phenyl of the pbpy ligand. This interaction provides a supramolecular cage formation that holds also in the excited states. Light-emitting electrochemical cells (LECs) using the novel complex show extraordinary lifetimes of approximately 2000 h. The high stability is favored by the presence of pendant methyl groups on the dmppz ligands that hinder the entrance of water molecules rendering the degradation of the complex more difficult.