Aggregation-induced phosphorescent emission (AIPE) of iridium(III) complexes

A novel aggregation-induced phosphorescent emission (AIPE) was observed for iridium(III) complexes. This interesting phenomenon was attributed to the intermolecular packing, resulting in a switch from the non-emissive 3LX excited state to the emissive 3MLLCT transition, which is confirmed by X-ray diffraction studies as well as theoretical calculations.     

Highly efficient phosphorescent iridium (III) diazine complexes for OLEDs: Different photophysical property between iridium (III) pyrazine complex and iridium (III) pyrimidine complex

The synthesis and luminescence of four new iridium (III) diazine complexes (1-4) were investigated. HOMO and LUMO energy levels of the complexes were estimated according to the electrochemical performance and the UV-Vis absorption spectra, showing the pyrimidine complexes have a larger increase for the LUMO than the HOMO orbital in comparison with the pyrazine complexes. Several high-efficiency yellow and green OLEDs based on phosphorescent iridium (III) diazine complexes were obtained. The devices emitting yellow light based on 1 with turn-on voltage of 4.1 V exhibited an external quantum efficiency of 13.2% (power efficiency 20.3 lm/W), a maximum current efficiency of 37.3 cd/A. The electroluminescent performance for the green iridium pyrimidine complex of 3 is comparable to that of the iridium pyridine complex (PPY)₂Ir(acac) (PPY = 2-phenylpyridine), which is among the best reported.     

Acid-induced degradation of phosphorescent dopants for OLEDs and its application to the synthesis of tris-heteroleptic iridium(III) bis-cyclometalated complexes

Investigations of blue phosphorescent organic light emitting diodes (OLEDs) based on [Ir(2-(2,4-difluorophenyl)pyridine)(2)(picolinate)] (FIrPic) have pointed to the cleavage of the picolinate as a possible reason for device instability. We reproduced the loss of picolinate and acetylacetonate ancillary ligands in solution by the addition of Br?nsted or Lewis acids. When hydrochloric acid is added to a solution of a [Ir(C^N)(2)(X^O)] complex (C^N = 2-phenylpyridine (ppy) or 2-(2,4-difluorophenyl)pyridine (diFppy) and X^O = picolinate (pic) or acetylacetonate (acac)), the cleavage of the ancillary ligand results in the direct formation of the chloro-bridged iridium(III) dimer [{Ir(C^N)(2)(μ-Cl)}(2)]. When triflic acid or boron trifluoride are used, a source of chloride (here tetrabutylammonium chloride) is added to obtain the same chloro-bridged iridium(III) dimer. Then, we advantageously used this degradation reaction for the efficient synthesis of tris-heteroleptic cyclometalated iridium(III) complexes [Ir(C^N(1))(C^N(2))(L)], a family of cyclometalated complexes otherwise challenging to prepare. We used an iridium(I) complex, [{Ir(COD)(μ-Cl)}(2)], and a stoichiometric amount of two different C^N ligands (C^N(1) = ppy; C^N(2) = diFppy) as starting materials for the swift preparation of the chloro-bridged iridium(III) dimers. After reacting the mixture with acetylacetonate and subsequent purification, the tris-heteroleptic complex [Ir(ppy)(diFppy)(acac)] could be isolated with good yield from the crude containing as well the bis-heteroleptic complexes [Ir(ppy)(2)(acac)] and [Ir(diFppy)(2)(acac)]. Reaction of the tris-heteroleptic acac complex with hydrochloric acid gives pure heteroleptic chloro-bridged iridium dimer [{Ir(ppy)(diFppy)(μ-Cl)}(2)], which can be used as starting material for the preparation of a new tris-heteroleptic iridium(III) complex based on these two C^N ligands. Finally, we use DFT/LR-TDDFT to rationalize the impact of the two different C^N ligands on the observed photophysical and electrochemical properties.     

Synthesis of a highly phosphorescent emitting iridium(III) complex and its application in OLEDs

A rigid ligand benzo[de]benzo[4,5]imidazo[2,1-α]isoquinolin-7-one (biio) was designed and conveniently synthesized, and the corresponding bis-cyclometalated iridium complex (biio)₂Ir(acac) (acac = acetylacetone) was prepared. The light emitting and electrochemical properties of this complex were studied. The complex has the characters of simply synthetic procedure and strong phosphorescence. The electroluminescent device using this complex as dopant was fabricated. The device had the structure of ITO/NPB (40 nm)/Ir complex:CBP (7%, 30 nm)/BCP (15 nm)/Alq₃ (30 nm)/LiF (1 nm)/Al (100 nm). The maximum emission of the device was at 496 nm. The maximum brightness of the device can reach 79640 cd m⁻² with an external quantum efficiency of 12.1% and a maximum current efficiency of 31.7 cd A⁻¹.     

Highly phosphorescent perfect green emitting iridium(iii) complex for application in OLEDs

A novel iridium complex, [bis-(2-phenylpyridine)(2-carboxy-4-dimethylaminopyridine)iridium(iii)] (N984), was synthesized and characterized using spectroscopic and electrochemical methods; a solution processable OLED device incorporating the N984 complex displays electroluminescence spectra with a narrow bandwidth of 70 nm at half of its intensity, with colour coordinates of x = 0.322; y = 0.529 that are very close to those suggested by the PAL standard for a green emitter.     

A theoretical study: Green phosphorescent iridium(III) complexes with low-efficiency roll-off

A series of heterocyclic Ir(III) complexes used in organic light-emitting diode (OLED) materials with low-efficiency roll-off performance have been studied theoretically. Their electronic structures, spectral properties, and their application value in OLEDs are discussed. The geometries, electronic structures, lowest-lying singlet absorptions, and triplet emissions of (dmdppr-dmp)₂Ir(dibm), and the theoretically designed models of (dmdppr-dmp)₂Ir(acac), (dmdppr-dmp)₂Ir(tpip), (dmdppr-Fdmp)₂Ir(dibm), (dmdppr-Fdmp)₂Ir(acac), and (dmdppr-Fdmp)₂Ir(tpip) were investigated with density-functional-theory-based approaches, where dibm denotes 2,6-dimethy-3,5-heptanedionato-κ₂-O,O′, acac denotes acetylacetonate, and tpip denotes tetraphenylimido-diphosphinate.     

Polymerizable cationic iridium(III) complexes exhibiting color tunable light emission and their corresponding conducting metallopolymers

Cyclometalated iridium(III) complexes have been synthesized for use in a variety of photophysical applications, including polymer light emitting diodes (PLEDs). A series of new complexes with one electrochemically polymerizable ligand and two phenylpyridine(ppy)-based ligands have been prepared: [Ir(ppy)₂L][PF₆](1), [Ir(F-mppy)₂L][PF₆](2), and [Ir(Br-mppy)₂L][PF₆](3), where L = 3,8-bis(2,2′-bithien-5-yl)-1,10-phenanthroline. The ancillary ppy ligands can be easily varied synthetically to tune emission color of the monomer from blue–green to red. The solid state structure of complex 1 has been obtained by single crystal X-ray crystallography. Conducting polymer materials have been prepared by electropolymerization of monomers and were characterized through XPS analysis and spectroscopic studies.     

Creation of cationic iridium(III) complexes with aggregation-induced phosphorescent emission (AIPE) properties by increasing rotation groups on carbazole peripheries

Three cationic iridium complexes containing 4,7-bis(3,6-di-tert-butyl-9H-carbazol-9-yl)-1,10-phenanthroline (L(1)) and 4,7-bis(3',6'-di-tert-butyl-6-(3,6-di-tert-butyl-9H-carbazol-9-yl)-3,9'-bi(9H-carbazol)-9-yl)-1,10-phenanthroline (L(2)) as the ancillary ligands, namely, [Ir(ppy)(2)(L(1))]PF(6) (1), [Ir(ppy)(2)(L(2))]PF(6) (2) and [Ir(oxd)(2)(L(2))]PF(6) (3) (ppy is 2-phenylpyridine, oxd is 2,5-diphenyl-1,3,4-oxadiazole), have been designed and prepared. With more intramolecular rotational units on the ancillary ligand (L(2)), 2 and 3 possess a unique aggregation-induced phosphorescent emission (AIPE) property. This phenomenon was unprecedentedly observed in the cationic iridium(III) complexes. In order to investigate the underlying mechanism of this AIPE behavior, their photophysical, temperature-dependent aggregation properties as well as theoretical calculations, were performed. The results suggest that restricted intramolecular rotation is responsible for the AIPE of cationic complexes. Moreover, photoluminescent quantum yields in the neat film, thermal stabilities and off/on luminescence switching of 2 were investigated, revealing its potential application as a candidate for LECs and organic vapor sensing.     

Physicochemical studies of green phosphorescent light-emitting materials from cyclometalated heteroleptic iridium(III) complexes

A series of novel imidazole ligands were synthesized and characterized. Phosphorescence studies of series of heteroleptic cyclometalated iridium(III) complexes reveal that these complexes possess dominantly (3)MLCT and (3)π-π* excited states and the solvent shifts of these complexes are interpreted by Richardt-Dimroth and Marcus solvent functions. The results consistent with prior assignments on the absorption band to a metal-to-ligand charge transfer excited state associated with chelating ligand. Emission kinetic studies exploited that the radiative transition (k(r)), increases with increasing λ(em) and linear correlation exists between ln(k(nr)) and energy gap. Electronic transition theory is applied to study the effect of E(g) and ΔQ(e) on non-radiative transition (k(nr)). With a larger ΔQ(e), favouring vibrational overlap and leading to a larger value for k(nr).     

Comment on 'aggregation-induced phosphorescent emission (AIPE) of iridium(III) complexes': origin of the enhanced phosphorescence

An investigation of the photophysics of Ir(iii) complexes with controlled ligand structures and our quantum chemical calculations attest that the most probable explanation for the reported 'aggregation-induced phosphorescent emission', which was originally claimed to be related to an intermolecular excimer, is restricted intramolecular motion.     

Synthesis and phosphorescent properties of two novel iridium (Ⅲ) complexes bearing bulky tert-butyl substituents

The synthesis and phosphorescence properties of two novel Ir(Ⅲ)complexes bearing tert-butyl substituents,bis(4-tert-butyl-2- phenylbenzothiozolato-N,C~(2′))iridium(Ⅲ)(acetylacetonate)[(tbt)_2Ir(acac)]and bis(4-tert-butyl-1-phenyl-1H-benzimidazolato- N,C~(2′))iridium(Ⅲ)(acetylacetonate)[(tpbi)_2Ir(acac)],are reported,their molecular structures are confirmed by~1H NMR,ESI-MS and elementary analysis.Photoluminescence(PL)studies revealed that they can emit strong green and orange phosphorescence in high quantum yields.Compared to their prototypes lacking of tert-butyl substituents,the two novel iridium(Ⅲ)complexes both have shorter lifetimes and improved or nearly similar PL quantum efficiencies,implying that the exciton quenching is inhibited effectively when molecular steric hindrance increases.The two chelates have great potential to be used as electrophosphorescent materials.     

Synthetically tailored excited states: phosphorescent, cyclometalated iridium(III) complexes and their applications

Phosphorescent iridium(III) complexes are being widely explored for their utility in diverse photophysical applications. The performance of these materials in such roles depends heavily on their excited-state properties, which can be tuned through ligand and substituent effects. This concept article focuses on methods for synthetically tailoring the properties of bis-cyclometalated iridium(III) materials, and explores the factors governing the nature of their lowest excited state.     

Aggregation induced colour change for phosphorescent iridium(III) complex-based anionic surfactants

We describe a new class of water soluble metallosurfactant molecules based on luminescent neutral iridium(III) complexes. The compounds possess an alkyl chain terminated with a negatively charged group, a sulphate. Due to their amphiphilic nature they assemble in aggregates in water and their photophysical properties, as well as the morphological characterization of the assemblies are presented. In particular, UV-Vis absorption, steady-state and time-resolved emission spectroscopy, dynamic light scattering and scanning electron microscopy techniques have been employed towards the analysis of the assemblies in different media. Comparison with the single components shows that the aggregates have very different photophysical properties. Importantly, the change in colour upon self-assembly is a remarkable feature which could be used for the design of probes which can change properties in different environments.     

Electrochemiluminescence of cyclometalated iridium (III) complexes

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Bright electrochemiluminescence of iridium(III) complexes

Electrochemiluminescence (ECL) of four bright iridium(III) complexes containing aryltriazole cyclometallated ligands is reported. The ECL mechanisms, spectra and high efficiencies via annihilation and coreactant paths have been investigated.     

Proximity effects on the phosphorescent properties of dinuclear salicylaldiminato cyclometalated iridium(III) complexes linked with polymethylene spacers

Transition Metal Chemistry - The synthesis, structure and photophysical properties of dinuclear bis(phenylpyridine)(salicylaldiminato)Ir(III) complexes bearing polymethylene linkers are described...     

Ruthenium(III) and iridium(III) complexes with nicotine

A new chloride-dimethylsulfoxide-ruthenium(III) complex with nicotine trans-[Ru^IIICl₄(DMSO)[H-(Nicotine)]] (1) and three related iridium(III) complexes; [H-(Nicotine)]trans-[Ir^IIICl₄(DMSO)₂] (2), trans-[Ir^IIICl₄(DMSO)[H-(Nicotine)]] (3) and mer-[Ir^IIICl₃(DMSO)(Nicotine)₂] (4) have been synthesized and characterized by spectroscopic techniques and by single crystal X-ray diffraction (1, 2, and 4). Protonated nicotine at pyrrolidine nitrogen is present in complexes 1 and 3 while two neutral nicotine ligands are observed in 4. In these three inner-sphere complexes coordination occurs through the pyridine nitrogen. Moreover, in the outer-sphere complex 2, an electrostatic interaction is observed between a cationic protonated nicotine at the pyrrolidine nitrogen and the anionic trans-[Ir^IIICl₄(DMSO)₂]^¯ complex.