σ-Hammett parameter: a strategy to enhance both photo- and electro-luminescence features of heteroleptic copper(i) complexes

This work studies the effect of the σ-Hammett parameter (σp) – i.e., the σ-donation effect caused by substitution at the para position of a bipyridine ligand (4,4′-R2bipy, where R is MeO, Me, H, NO2) – on both the photo- and electro-luminescence features of a series of heteroleptic copper(I) complexes – i.e., [Cu(N^N)(P^P)]+ where N^N and P^P ligands are R2bipy and Xantphos, respectively. By virtue of a comprehensive photophysical, theoretical, and thin-film lighting device – i.e., light-emitting electrochemical cells (LECs) – investigation, we note a clear relationship between the σp and the photo- and electro-luminescence parameters, such as photoluminescence quantum yields, excited-state…

Near-UV to red-emitting charged bis-cyclometallated iridium(iii) complexes for light-emitting electrochemical cells

Herein we report a series of charged iridium complexes emitting from near-UV to red using carbene-based N^C: ancillary ligands. Synthesis, photophysical and electrochemical properties of this series are described in detail together with X-ray crystal structures. Density Functional Theory calculations show that the emission originates from the cyclometallated main ligand, in contrast to commonly designed charged complexes using bidentate N^N ancillary ligands, where the emission originates from the ancillary N^N ligand. The radiative process of this series of compounds is characterized by relatively low photoluminescence quantum yields in solution that is ascribed to non-radiative deactivati…

Inside Front Cover: Long-Living Light-Emitting Electrochemical Cells - Control through Supramolecular Interactions (Adv. Mater. 20/2008)

Efficient blue emitting organic light emitting diodes based on fluorescent solution processable cyclic phosphazenes

Solution processable blue fluorescent dendrimers based on cyclic phosphazene (CP) cores incorporating amino-pyrene moieties have been prepared and used as emissive layers in organic light emitting diodes (OLEDs). These dendrimers have high glass transition temperatures, are monodisperse, have high purity via common chromatographic techniques, and form defect-free amorphous films via spin/dip coating. The solution processable blue light emitting OLEDs reach current efficiencies of 3.9 cd/A at brightness levels near 1000 cd/m2. Depending on the molecular bridge used to attach the fluorescent dendron to the inorganic core, the emission wavelength changes from 470 to 545 nm, corresponding to bl…

Lowest triplet excited states of a novel heteroleptic iridium(III) complex and their role in the emission colour

Abstract The [Ir(ppy-F 2 ) 2 Me 4 phen] +1 complex, where ppy-F 2 is 2-(2′,4′-fluorophenyl)pyridine and Me 4 phen is 3,4,7,8-tetramethyl-1,10-phenanthroline, has been theoretically investigated by means of DFT calculations. The molecular and electronic properties calculated for [Ir(ppy-F 2 ) 2 Me 4 phen] +1 are compared with those obtained for the simpler [Ir(ppy)(bpy)] +1 complex. The introduction of fluorine substituents in the ppy ligands and the use of phenanthroline instead of 2,2′-bipyridine as the diimine ligand increase the HOMO–LUMO energy gap and blue-shift the emission colour. The phenanthroline ligand causes the appearance of two nearly-degenerate LUMO orbitals of different symm…

ChemInform Abstract: Luminescent Ionic Transition Metal Complexes for Light-Emitting Electrochemical Cells

Higher efficiency in the end-use of energy requires substantial progress in lighting concepts. All the technologies under development are based on solid-state electroluminescent materials and belong to the general area of solid-state lighting (SSL). The two main technologies being developed in SSL are light-emitting diodes (LEDs) and organic light-emitting diodes (OLEDs), but in recent years, light-emitting electrochemical cells (LECs) have emerged as an alternative option. The luminescent materials in LECs are either luminescent polymers together with ionic salts or ionic species, such as ionic transition-metal complexes (iTMCs). Cyclometalated complexes of IrIII are by far the most utiliz…

Dumbbell-Shaped Dinuclear Iridium Complexes and Their Application to Light-Emitting Electrochemical Cells

A novel family of dumbbell- shaped dinuclear complexes in which an oligophenyleneethynylene spacer is linked to two heteroleptic iridiumA complexes is presented. The synthesis, as well as the electrochemical and pho- tophysical characterization of the new complexes, is reported. The experimen- tal results are interpreted with the help of density functional theory calcula- tions. From these studies we conclude that the lowest triplet excited state cor- responds to a 3 p-p* state located on the conjugated spacer. The presence of this state below the 3 MLCT/ 3 LLCT emitting states of the end-capping Ir III complexes explains the low quantum yields observed for the dinuclear com- plexes (one or…

Efficient and Long-Living Light-Emitting Electrochemical Cells

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…

A Supramolecularly-Caged Ionic Iridium(III) Complex Yielding Bright and Very Stable Solid-State Light-Emitting Electrochemical Cells

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.

Lumineszierende ionische Übergangsmetallkomplexe für leuchtende elektrochemische Zellen

Durch die Umsetzung neuer Beleuchtungskonzepte konnte die Verwertung von Energie deutlich effizienter gestaltet werden. Alle derzeit entwickelten Technologien beruhen auf elektrolumineszierenden Festkorpern und lassen sich allgemein als Festkorperbeleuchtung (solid-state lighting, SSL) einstufen. Die beiden wichtigsten Zweige der SSL-Technologie sind Leuchtdioden (LEDs) und organische Leuchtdioden (OLEDs), doch seit kurzem bilden auch leuchtende elektrochemische Zellen (LECs) eine Alternative, die als aktive Materialien entweder lumineszierende Polymere in Kombination mit ionischen Salzen oder lumineszierende ionische Spezies wie ionische Ubergangsmetallkomplexe (iTMCs) enthalten. Cyclometa…

Deep-Red-Emitting Electrochemical Cells Based on Heteroleptic Bis-chelated Ruthenium(II) Complexes

Two ruthenium(II)-based complexes were prepared that show intense deep-red light emission at room temperature. Solid-state electroluminescent devices were prepared using one of the ruthenium complexes as the only active component. These devices emit deep-red light at low voltages and exhibit extraordinary stabilities, demonstrating their potential for low-cost deep-red light sources.

Improved stability of solid state light emitting electrochemical cells consisting of ruthenium and iridium complexes

ABSTRACTTwo charged organometallic complexes containing bulky hydrophobic ligands based on ruthenium (II) and iridium (III) were synthesized and their performance in solid state light emitting electrochemical cells is described. The complexes were chosen as due to their large ligands a diminished susceptibility towards the formation of destructive complexes during device operation is expected. The LEC device performances reveal the longest living devices reported so far under dc bias. Quantum chemical calculations confirm that the major effect of the bulky diphenylphenanthroline ligands is of steric origin and not related with changes in the molecular electronic structure of the complexes.

Light-emitting electrochemical cells based on a supramolecularly-caged phenanthroline-based iridium complex.

The complex [Ir(ppy)(2)(pphen)][PF(6)] (Hppy = 2-phenylpyridine, pphen = 2-phenyl-1,10-phenanthroline) has been prepared and evaluated as an electroluminescent component for light-emitting electrochemical cells (LECs). Like in analogous LECs using bpy-based iridium(III) complexes a significant enhancement of the device stability is observed.

Impact of the synergistic collaboration of oligothiophene bridges and ruthenium complexes on the optical properties of dumbbell-shaped compounds.

The linear and non-linear optical properties of a family of dumbbell-shaped dinuclear complexes, in which an oligothiophene chain with various numbers of rings (1, 3, and 6) acts as a bridge between two homoleptic tris(2,2'-bipyridine)ruthenium(II) complexes, have been fully investigated by using a range of spectroscopic techniques (absorption and luminescence, transient absorption, Raman, and non-linear absorption), together with density functional theory calculations. Our results shed light on the impact of the synergistic collaboration between the electronic structures of the two chemical moieties on the optical properties of these materials. Experiments on the linear optical properties …

Red-light-emitting electrochemical cell using a polypyridyl iridium(III) polymer.

A deep-red phosphorescent ionic iridium(III) complex is prepared and incorporated into a polymer. Both the complex (1) and the polymer (2) were used as the single active material in solid-state light-emitting electrochemical cells (LECs). The devices built up using 1 and 2 emit in the deep-red region of the visible spectrum with CIE coordinates x = 0.710; y = 0.283 and x = 0.691; y = 0.289, respectively, making them one of the deepest-red emitting LECs reported. It is the first example of a polymeric LEC incorporating an ionic iridium complex, which exhibits increased stabilities compared with the device based on the small molecular weight complex.

Origin of the large spectral shift in electroluminescence in a blue light emitting cationic iridium(III) complex

A new, but archetypal compound [ Ir( ppy- F-2) (2)Me(4)phen] PF6, where ppy- F2 is 2-(2',4'- fluorophenyl) pyridine and Me(4)phen is 3,4,7,8- tetramethyl- 1,10- phenanthroline, was synthesized and used to prepare a solid-state light-emitting electrochemical cell (LEEC). This complex emits blue light with a maximum at 476 nm when photoexcited in a thin film, with a photoluminescence quantum yield of 52%. It yields an efficient single-component solid-state electroluminescence device with a current efficiency reaching 5.5 cd A(-1) and a maximum power efficiency of 5.8 Lm Watt(-1). However, the electroluminescence spectrum is shifted with respect to the photoluminescence spectrum by 80 nm resul…

Copper(i) complexes for sustainable light-emitting electrochemical cells

Four prototype heteroleptic copper(I) complexes [Cu(bpy)(pop)][PF6] (bpy = 2,2′-bipyridine, pop = bis(2-(diphenylphosphino)phenyl)ether), [Cu(phen)(pop)][PF6] (phen = 1,10-phenanthroline), [Cu(bpy)(pdpb)][PF6] (pdpb = 1,2-bis(diphenylphosphino)benzene) and [Cu(phen)(pdpb)][PF6] are presented. The synthesis, X-ray structures, solution and solid-state photophysical studies, and the performance in light-emitting electrochemical cells (LECs) of these complexes are described. Their photophysical properties are interpreted with the help of density functional theory (DFT) calculations. The photophysical studies in solution and in the solid-state indicate that these copper(I) complexes show good lu…

Recent advances in light-emitting electrochemical cells

Light-emitting electrochemical cells (LECs) are solution-processable thin-film electroluminescent devices consisting of a luminescent material in an ionic environment. The simplest type of LEC is based on only one material, ionic transition-metal complexes (iTMCs). These materials are of interest for different scientific fields such as chemistry, physics, and technology as selected chemical modifications of iTMCs resulted in crucial breakthroughs for the performance of LECs. This short review highlights the different strategies used to design these compounds with the aim to enhance the performances of LECs.

Improving the Turn-On Time of Light-Emitting Electrochemical Cells without Sacrificing their Stability

The luminance, efficiency, and turn-on time of ionic iridium complex-based light-emitting electrochemical cells can be improved by inserting an ionic liquid with high intrinsic conductivity. This results in a device in which the decrease in turn-on time is achieved while maintaining the stability.

Photoluminescent Cu(i) vs. Ag(i) complexes: slowing down emission in Cu(i) complexes by pentacoordinate low-lying excited states.

This work describes the synthesis, and structural, spectroscopic, and theoretical studies of a mononuclear silver(i) complex with the formula [Ag(Xantphos)(4,4'-(MeO)2-2,2'-bipy)]BF4·DCM (1·BF4) [Xantphos: 4,5-bis(diphenylphosphino)-9,9'-dimethylxanthene]. We provide meaningful insights into the enhancement of the photoluminescence features of this silver(i) complex compared to its copper(i) analogue.

Near-Quantitative Internal Quantum Efficiency in a Light-Emitting Electrochemical Cell

A green-light-emitting iridium(III) complex was prepared that has a photoluminescence quantum yield in a thin-film configuration of almost unity. When used in a simple solid-state single-layer light-emitting electrochemical cell, it yielded an external quantum efficiency of nearly 15% and a power efficiency of 38 Lm/W. We argue that these high external efficiencies are only possible if near-quantitative internal electron-to-photon conversion occurs. This shows that the limiting factor for the efficiency of these devices is the photoluminescence quantum yield in a solid film configuration. The observed efficiencies show the prospect of these simple electroluminescent devices for lighting and…

Tuning the Self-Assembly of Rectangular Amphiphilic Cruciforms

The self-assembly of a series of nonionic amphiphilic cruciforms based on the 1,2,4,5-tetrakis(phenylethynyl)benzene (TPEB) skeleton, in which the peripheral substituents have been modified to modulate the morphology of the supramolecular structures, is reported. The presence of linear paraffinic and hydrophilic chains in TPEBs 1 and 2 gives rise to two-dimensional structures of high aspect ratio. In contrast, the incorporation of dendronized hydrophilic chains results in the formation of twisted ribbons in amphiphile 3 and impedes the organized self-assembly of TPEB 4. Theoretical calculations show that the self-assembly of these amphiphiles might be initiated with the formation of π-stack…

Efficient deep-red light-emitting electrochemical cells based on a perylenediimide-iridium-complex dyad

A two-layer light-emitting electrochemical cell device based on a new perylenediimide-iridium-complex dyad is presented emitting in the deep-red region with high external quantum efficiencies (3.27%). Costa Riquelme, Ruben Dario, Ruben.Costa@uv.es ; Orti Guillen, Enrique, Enrique.Orti@uv.es ; Bolink, Henk, Henk.Bolink@uv.es ; Gierschner, Johannes, Johannes.Gierschner@uv.es

Deciphering the Electroluminescence Behavior of Silver(I)‐Complexes in Light‐Emitting Electrochemical Cells: Limitations and Solutions toward Highly Stable Devices

Long-Living Light-Emitting Electrochemical Cells - Control through Supramolecular Interactions

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.

Zn(II)-coordination and fluorescence studies of a new polyazamacrocycle incorporating 1H-pyrazole and naphthalene units.

The synthesis and Zn(2+) coordination properties of a new macrocycle (L1) obtained by dipodal (2 + 2) condensation of the polyamine 3-(naphthalen-2-ylmethyl)pentane-1,5-diamine with 1H-pyrazole-3,5-dicarbaldehyde are reported. pH-metric studies show that L1 bears five measurable protonation steps in the 2.0-11.0 pH range. Fluorescence emission studies indicate that the removal of the first proton from the H(5)L1(5+) species leads to a significant decrease in the emission due to a photoinduced electron transfer process. Addition of Zn(2+) promotes a boat-like conformation that approaches both fluorophores and facilitates the formation of an excimer which reaches its highest emission for a 1 …

Stable and Efficient Solid-State Light-Emitting Electrochemical Cells Based on a Series of Hydrophobic Iridium Complexes

Light-emitting electrochemical cells (LECs) based on ionic transition-metal complexes (iTMCs) exhibiting high efficiency, 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)…

Long-Living Emitting Electrochemical Cells Based on Supramolecular π-π Interactions

AbstractThe complex [Ir(ppy)2(dpbpy)][PF6] (Hppy = 2-phenylpyridine, dpbpy = 6,6'-diphenyl-2,2'-bipyridine) has been prepared and evaluated as an electroluminescent component for light-emitting electrochemical cells (LECs). The complex exhibits two intramolecular face-to-face π-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'-bipyridine with only one π-stacking interaction.

Archetype Cationic Iridium Complexes and Their Use in Solid-State Light-Emitting Electrochemical Cells

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 counter…

Two are not always better than one: ligand optimisation for long-living light-emitting electrochemical cells

The complex [Ir(ppy)2(dpbpy)][PF6] (Hppy = 2-phenylpyridine, dpbpy = 6,6'-diphenyl-2,2'-bipyridine) has been prepared and evaluated as an electroluminescent component for light-emitting electrochemical cells (LECs); the complex exhibits two intramolecular face-to-face π-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'-bipyridine. Costa Riquelme, Ruben Dario, Ruben.Costa@uv.es ; Orti Guillen, Enrique, Enrique.Orti@uv.es ; Bolink, Henk, Henk.Bolink@uv.es

Simple, Fast, Bright, and Stable Light Sources

In this work we show that solution-processed light-emitting electrochemical cells (LECs) based on only an ionic iridium complex and a small amount of ionic liquid exhibit exceptionally good performances when applying a pulsed current: sub-second turn-on times and almost constant high luminances (>600 cd m(-2) ) and power efficiencies over the first 600 h. This demonstrates the potential of LECs for applications in solid-state signage and lighting.

Intramolecular pi-stacking in a phenylpyrazole-based iridium complex and its use in light-emitting electrochemical cells.

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 d…

Solid-State Lighting: Simple, Fast, Bright, and Stable Light Sources (Adv. Mater. 7/2012)

Single Molecule Solid State Light Emitting Electrochemical Cells with Lifetimes Superior to 3000 Hours

Do the Intramolecular π Interactions Improve the Stability of Ionic, Pyridine-Carbene-Based Iridium(III) Complexes?

Throughout the last years one of the most intensive research topics in light-emitting electrochemical cells (LECs) focused on the design of blue-emitting, ionic iridium(III) complexes. To this end, the most recent strategy is the use of carbene-based ancillary ligands. Although blue LECs have been successfully fabricated, the stability has been noted as the main drawback. To overcome this problem, Zhang et al. have recently explored the use of π interactions to enhance the strength of pyridine-carbene-based complexes. The authors suggested that the use of intramolecular π–π stacking interactions by means of pendant phenyl rings to improve the stability of LECs is not as effective as in devi…

Luminescent Ionic Transition-Metal Complexes for Light-Emitting Electrochemical Cells

Higher efficiency in the end-use of energy requires substantial progress in lighting concepts. All the technologies under development are based on solid-state electroluminescent materials and belong to the general area of solid-state lighting (SSL). The two main technologies being developed in SSL are light-emitting diodes (LEDs) and organic light-emitting diodes (OLEDs), but in recent years, light-emitting electrochemical cells (LECs) have emerged as an alternative option. The luminescent materials in LECs are either luminescent polymers together with ionic salts or ionic species, such as ionic transition-metal complexes (iTMCs). Cyclometalated complexes of Ir(III) are by far the most util…

CCDC 1897433: Experimental Crystal Structure Determination

Related Article: José M. Carbonell-Vilar, Elisa Fresta, Donatella Armentano, Rubén D. Costa, Marta Viciano-Chumillas, Joan Cano|2019|Dalton Trans.|48|9765|doi:10.1039/C9DT00772E

CCDC 871500: Experimental Crystal Structure Determination

Related Article: Edwin C. Constable, Markus Neuburger, Pirmin Rösel, Gabriel E. Schneider, Jennifer A. Zampese, Catherine E. Housecroft, Filippo Monti, Nicola Armaroli, Rubén D. Costa, and Enrique Ortí|2013|Inorg.Chem.|52|885|doi:10.1021/ic302026f

CCDC 1897434: Experimental Crystal Structure Determination

Related Article: Elisa Fresta, José M. Carbonell‐Vilar, Jiayin Yu, Donatella Armentano, Joan Cano, Marta Viciano‐Chumillas, Rubén D. Costa|2019|Adv.Funct.Mater.||1901797|doi:10.1002/adfm.201901797

CCDC 871501: Experimental Crystal Structure Determination

Related Article: Edwin C. Constable, Markus Neuburger, Pirmin Rösel, Gabriel E. Schneider, Jennifer A. Zampese, Catherine E. Housecroft, Filippo Monti, Nicola Armaroli, Rubén D. Costa, and Enrique Ortí|2013|Inorg.Chem.|52|885|doi:10.1021/ic302026f

CCDC 1522134: Experimental Crystal Structure Determination

Related Article: Michael D. Weber, Marta Viciano-Chumillas, Donatella Armentano, Joan Cano, Rubén D. Costa|2017|Dalton Trans.|46|6312|doi:10.1039/C7DT00810D

CCDC 1522132: Experimental Crystal Structure Determination

Related Article: Michael D. Weber, Marta Viciano-Chumillas, Donatella Armentano, Joan Cano, Rubén D. Costa|2017|Dalton Trans.|46|6312|doi:10.1039/C7DT00810D

CCDC 1522135: Experimental Crystal Structure Determination

Related Article: Michael D. Weber, Marta Viciano-Chumillas, Donatella Armentano, Joan Cano, Rubén D. Costa|2017|Dalton Trans.|46|6312|doi:10.1039/C7DT00810D

CCDC 1897435: Experimental Crystal Structure Determination

Related Article: Elisa Fresta, José M. Carbonell‐Vilar, Jiayin Yu, Donatella Armentano, Joan Cano, Marta Viciano‐Chumillas, Rubén D. Costa|2019|Adv.Funct.Mater.||1901797|doi:10.1002/adfm.201901797

CCDC 1522133: Experimental Crystal Structure Determination

Related Article: Michael D. Weber, Marta Viciano-Chumillas, Donatella Armentano, Joan Cano, Rubén D. Costa|2017|Dalton Trans.|46|6312|doi:10.1039/C7DT00810D

CCDC 871502: Experimental Crystal Structure Determination

Related Article: Edwin C. Constable, Markus Neuburger, Pirmin Rösel, Gabriel E. Schneider, Jennifer A. Zampese, Catherine E. Housecroft, Filippo Monti, Nicola Armaroli, Rubén D. Costa, and Enrique Ortí|2013|Inorg.Chem.|52|885|doi:10.1021/ic302026f