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This article explores the development of phosphorescent organometallic complexes, specifically platinum(II) complexes with phenylpyridine and N-heterocyclic carbene (NHC) ligands, for use in electroluminescent devices. The focus is on understanding the correlation between the electronic properties of the ligands and the photophysical properties of the emitters. The study finds that structural modifications of the ligands strongly influence the electronic and photophysical properties of the complexes. The complexes exhibit good to very good sky-blue phosphorescent emission and may have potential applications as photocatalysts. The article also provides a detailed account of the synthesis and characterization of several complex compounds. [Extracted from the article]

Orthoplatinated complexes [Pt(C^C*)(acac)] (1R), in which C^C* is orthoplatinated 3-R-1-phenyl-1H-benzo[d]imidazol-2-ylidene and R = Me and Ph, reacted with 1′-(diphenylphosphino)ferrocene-1-carboxylic acid (Hdpf) under protonation of the acetylacetonate ligand (acac) to produce the corresponding phosphinocarboxylate bischelate complexes [Pt(C^C*)(dpf-κ2O,P)] (2R) as single isomers with trans-P,C(carbene) geometry. The compounds were fully characterized by elemental analysis, spectroscopic methods, single-crystal X-ray diffraction analysis, and cyclic voltammetry. In addition, DFT calculations were used to determine differences in energy and the bonding situation between 2R and the hypothetical geometric isomers 3R with a trans-P,C(phenyl) arrangement. The experimental and theoretical results are consistent with the antisymbiosis effect observed in complexes of soft metal ions, namely with weakening of Pt–C bonds by strongly trans-influencing ligands. [ABSTRACT FROM AUTHOR]

Platinum(II) complexes with rigid and electron donating ligands are efficient phosphorescent emitters at room temperature. However, the excited‐state lifetimes of these complexes are, in general, relatively long. This problem, which can result in the degradation of the emitter, can be overcome by exploiting the natural tendency of platinum to form metallophilic interactions and aggregates. Herein, we report platinum(II) bimetallic complexes with 100 % quantum yield and at the same time exceptionally short radiative decay times, which in some cases are up to a hundredfold faster than the analogous monometallic complexes. [ABSTRACT FROM AUTHOR]

The structural motif of platinum(II) complexes bearing cyclometalating N‐heterocyclic carbene ligands can be used to design deep‐blue phosphors for application in organic light‐emitting diodes. However, the photophysical properties of the resulting molecules are also highly dependent on the auxiliary ligand. These often allow molecular deformations in the excited state which contribute to non‐radiative decay processes that diminish the attainable quantum yield. The use of bis(pyrazolyl)borate‐based auxiliary ligands enforces a high molecular rigidity due to their unique geometry. The steric crowding in the coordination sphere inhibits deformation processes and results in highly efficient deep‐blue platinum(II) emitters with CIE coordinates below (0.15; 0.15). [ABSTRACT FROM AUTHOR]

Platin(II)‐Komplexe mit cyclometallierten N‐heterocyclischen Carbenliganden können verwendet werden, um tiefblaue Emitter zur Anwendung in organischen Leuchtdioden zu entwickeln. Die photophysikalischen Eigenschaften der resultierenden Moleküle sind jedoch auch stark abhängig von dem eingesetzten Hilfsliganden. Im angeregten Zustand erlauben diese oft Moleküldeformationen, die zu strahlungslosen Relaxationsprozessen führen und damit die erreichbare Quantenausbeute schmälern. Die Verwendung von auf Bis(pyrazolyl)boraten basierenden Hilfsliganden erzwingt aufgrund ihrer tetraedrischen Geometrie eine hohe molekulare Rigidität. Der erhöhte sterische Anspruch der Liganden in der Koordinationssphäre hemmt Deformationsprozesse und führt zu hocheffizienten, tiefblauen Platin(II)‐Emittern mit CIE‐Koordinaten unterhalb von (0.15; 0.15). [ABSTRACT FROM AUTHOR]

Iridium(III) complexes with cyclometalating ligands can achieve excellent properties for use as phosphorescent emitters in organic light emitting diodes. A series of complexes with 2‐phenyl‐pyridine and bis(pyrazolyl)borate ligands was investigated with regard to this application. The sky‐blue to green emitters showed nearly unitary quantum yields and short excited state lifetimes. [ABSTRACT FROM AUTHOR]

Platinum(II) complexes with an N‐heterocyclic carbene and a cyclometalating phenyl ligand (C^C*) are excellent candidates as efficient blue triplet emitters for OLED applications. The electronic and photophysical properties of these complexes can be fine‐tuned with the objective to increase the quantum yields and lower the phosphorescence decay times. We found that platinum complexes with an imidazopyrazine C^C* ligand and bulky acetylacetonates are sky‐blue triplet emitters, characterised by an almost unitary quantum yield and short phosphorescence decay times. [ABSTRACT FROM AUTHOR]

Mesoionic carbene ligands based on 1,2,3‐triazole platforms can be used in cyclometalated platinum(II) complexes to achieve an efficient phosphorescence even at room temperature. In this report, 1,2,3‐triazolo[1,5‐a]pyridine‐3‐ylidenes are employed in such molecules along with β‐diketonates with varying steric demand. For full structural characterization, NMR spectroscopy and XRD experiments were employed. The photophysical properties were studied in solid poly(methyl methacrylate) (PMMA) matrices, as well as dichloromethane solutions. In PMMA, the synthesized complexes show quantum yields of 47–54 % with emission bands in the yellow region of the visible spectrum. Cyclic voltammetry measurements along with DFT calculations helped to assign the nature of the observed emissions. [ABSTRACT FROM AUTHOR]

Platinum(II) complexes with mesoionic C∧C *‐cyclometalating 1,2,3‐triazolylidene ligands are highly efficient phosphorescent emitters. Herein we report a series of this type bearing dibenzofuranyl‐substituted carbenes along with different β‐diketonate auxiliary ligands. They show luminescence in the green region of the visible spectrum and quantum yields of up to 78 % at room temperature. The proposed molecular structures were verified by NMR spectroscopy and X‐ray diffraction experiments which prove the formation of the mesoionic carbene. Additionally, DFT calculations and cyclic voltammetry measurements were used to rationalize the observed photophysical properties of the reported complexes. [ABSTRACT FROM AUTHOR]

Platinum(II) complexes [Pt(C^C*)(acac)], where C^C* = 3‐R‐1‐(phenyl‐κC2)‐1H‐benzimidazol‐2‐ylidene‐κC2 (R = Me, Ph) and acac = pentane‐2,4‐dionate, reacted with functionalized acetic acids YCH2CO2H (Y = NMe2, SMe and PPh2) with elimination of acetylacetone to produce the bis‐chelate complexes of the type [Pt(C^C*)(YCH2CO2)]. Whereas the Pt(II) precursor with the less bulky methyl substituent (R) gave rise to single products having trans‐C(NHC),Y geometry, its phenyl congener reacted less selectively, affording exclusively the product with trans‐S,C(Ph) configuration for Y = SMe and mixtures of cis and trans isomers for Y = NMe2 and PPh2. These observations were well reproduced by different DFT functionals at the double‐ξ level of theory, which suggested rather small energy differences between the geometric isomers. The photophysical measurements showed that complexes [Pt(C^C*)(YCH2CO2)] are emissive in the blue region (λem 460–490 nm) with photoluminescence quantum yields up to 36 % and emission lifetimes in the range of 3–5 µs. [ABSTRACT FROM AUTHOR]

We present the synthesis and characterization of cyclometalated ruthenium(II) NHC complexes with phenyl‐substituted imidazo[1,5‐a]pyridine C^C* ligands. The corresponding p‐cymene complexes can be reacted with bipyridine to form bisheteroleptic ruthenium(II) dyes. The compounds have been characterized by one‐ and two‐dimensional 1H/13C NMR spectroscopy, elemental analysis, cyclic voltammetry, infrared spectroscopy, as well as solid‐state structure (X‐ray) analysis. [ABSTRACT FROM AUTHOR]

We present a new class of tunable aryl alkyl ionic liquids (TAAILs) containing different palladate counter ions. Solid‐state structures for representative compounds have been obtained. Their properties are presented in comparison to those of newly synthesized and reported palladate ionic liquids with conventional counter ions. It was found that the aryl substitution pattern and the type of anion have a profound influence on the melting point. The speciation of the different anions in solution has been rationalized by DFT calculations. Customize, adapt, overcome: Ionic liquids containing a palladate anion are accessible in a very flexible synthetic procedure. The choice of aryl substituent, alkyl group, type of palladate counter ion and halide ligand can all be modified to allow for fine‐tuning of the properties of a wide range of new compounds. [ABSTRACT FROM AUTHOR]

We present a new class of dicationic palladium NHC complexes with two carbene ligands bearing different aryl substituents and a hemilabile pyrimidyl group. They can either be synthesized from the imidazolium salts via the silver transmetalation route to a halide-free palladium(ii) precursor or by direct deprotonation by palladium acetate. For four complexes we could determine their solid-state structures by X-ray diffraction experiments. Insight gained by NMR spectroscopy and DFT calculations revealed that in solution the two potentially bidentate ligands interchange between chelating and non-chelating coordination modes. The preference of these coordination modes is governed by the steric influence of the different ligands. The complexes were shown to be active catalysts for the hydroarylation of alkynes, and their performance was rationalized by DFT calculations. [ABSTRACT FROM AUTHOR]

The synthesis and characterization of the first bidentate C^C* cyclometalated platinum(II) complexes based on abnormal N‐heterocyclic carbenes (aNHC) is presented. The aNHC ligand precursors are prepared from benzonitriles and anilines to form 1,2,3‐trisubstituted imidazolium salts. The title compounds were synthesized by in situ generation of the silver carbene complex, followed by transmetalation to platinum and subsequent introduction of the β‐diketonate ligand. Structural characterization by 2D NMR experiments, as well as solid‐state structures unequivocally prove the abnormal binding mode of the aNHC ligands. Additionally, the photophysical properties of the platinum(II) complexes were examined and studied in detail by DFT calculations and cyclic voltammetry experiments. The title compounds proved to be strongly emissive at room temperature in the green to orange region of the visible spectrum, with emission efficiencies of up to 69 %. Photoluminescent platinum: The synthesis and characterization of the first platinum(II) complexes with C^C* cyclometalated aNHC ligands is reported. The abnormal binding mode was unequivocally confirmed by solid‐state structures and NMR experiments. Photoluminescence measurements, accompanied by DFT calculations and electrochemistry experiments, allowed insight into the emission characteristics of this class of compounds. [ABSTRACT FROM AUTHOR]

Abstract: Control of the excited state geometry by rational ligand design leads to a new class of phosphorescent emitters with extraordinary photophysical properties. Extension of the π‐system in the triplet state leading to a significant bathochromic shift of the emission was avoided by introduction of additional steric demand. We report the synthesis, characterization and photophysical properties of novel platinum(II) complexes bearing C^C* cyclometalated mesoionic carbene (MIC) with different β‐diketonate ligands. The MIC ligand precursors were prepared from 1‐phenyl‐1,2,3‐triazole using arylation protocols, introducing phenyl or mesityl functionalities. A solid state structure confirming the NMR assignments is presented. The emission properties were investigated in detail at room temperature and 77 K and are supported by DFT calculations and cyclic voltammetry. All complexes, with emission maxima between 502–534 nm, emit with quantum efficiencies ranging from 70–84 % in PMMA films. [ABSTRACT FROM AUTHOR]

The synthesis and characterization of cyclometalated C^C* platinum(II) complexes with unique photophysical properties, aggregation induced enhancement of the quantum yields with a simultaneous decrease of phosphorescence lifetimes, is reported. Additionally, a change of emission color is induced by variation of the excitation wavelength. The aggregation behavior of these complexes is controlled by the steric demand of the substituents. The photophysical properties of these complexes are investigated through emission-excitation matrix analysis (EEM). The monomeric complexes are excellent room temperature phosphorescent blue emitters with emission maxima below 470 nm and quantum yields of up to 93 %. [ABSTRACT FROM AUTHOR]

The synthesis and characterization of eight unprecedented phosphorescent CC* cyclometalated mesoionic aryl-1,2,3-triazolylidene platinum(II) complexes with different b-diketonate ligands are reported. All compounds proved to be strongly emissive at room temperature in poly(methyl methacrylate) films with an emitter concentration of 2 wt%. The observed photoluminescence properties were strongly dependent on the substitution on the aryl system and the b-diketonate ligand. Compared to acetylacetonate, the b-diketonates with aromatic substituents (mesityl and duryl) were found to significantly enhance the quantum yield while simultaneously reducing the emission lifetimes. Characterization was carried out by standard techniques, as well as solid-state structure determination, which confirmed the binding mode of the carbene ligand. DFT calculations, carried out to predict the emission wavelength with maximum intensity, were in excellent agreement with the (later) obtained experimental data. [ABSTRACT FROM AUTHOR]

Frontispiece: Sky-Blue Triplet Emitters with Cyclometalated Imidazopyrazine-Based NHC-Ligands and Aromatic Bulky Acetylacetonates Keywords: blue triplet emitters; N-heterocyclic carbenes; OLEDs; phosphorescence; quantum yields Blue triplet emitters, N-heterocyclic carbenes, OLEDs, phosphorescence, quantum yields. [Extracted from the article]

We present a new class of dicationic palladium NHC complexes with two carbene ligands bearing different aryl substituents and a hemilabile pyrimidyl group. They can either be synthesized from the imidazolium salts via the silver transmetalation route to a halide-free palladium(ii) precursor or by direct deprotonation by palladium acetate. For four complexes we could determine their solid-state structures by X-ray diffraction experiments. Insight gained by NMR spectroscopy and DFT calculations revealed that in solution the two potentially bidentate ligands interchange between chelating and non-chelating coordination modes. The preference of these coordination modes is governed by the steric influence of the different ligands. The complexes were shown to be active catalysts for the hydroarylation of alkynes, and their performance was rationalized by DFT calculations.

The synthesis and characterization of cyclometalated C^C* platinum(II) complexes with unique photophysical properties, aggregation induced enhancement of the quantum yields with a simultaneous decrease of phosphorescence lifetimes, is reported. Additionally, a change of emission color is induced by variation of the excitation wavelength. The aggregation behavior of these complexes is controlled by the steric demand of the substituents. The photophysical properties of these complexes are investigated through emission-excitation matrix analysis (EEM). The monomeric complexes are excellent room temperature phosphorescent blue emitters with emission maxima below 470 nm and quantum yields of up to 93 %., (© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)