Blue light emission from cyclometallated iridium(III) cyano complexes: Syntheses, crystal structures, and photophysical properties

Nanocomposite Scintillators Loaded With Hafnium Oxide and Phosphorescent Host and Guest for Gamma Spectroscopy

Gamma sensitive plastic scintillators are of critical importance in the fields of nuclear nonproliferation, medical imaging, and high energy physics. However, there is often a trade-off between high light yield and high loading of high-Z components, both of which play an essential role in gamma ray detection. This work takes advantage of triplet exciton harvesting to increase gamma light yield by utilizing 1,3-di(9H-carbazol-9-yl)benzene and 9,9-dimethyl-9H-fluorene as triplet hosts to facilitate Dexter energy transfer to bis[2-(4,6-difluorophenyl)pyridinato-C2,N](picolinato)iridium(III) (FIrPic), a blue light emitting phosphorescent dye. A plastic scintillator containing 20 wt % MF, 10 wt % mCP, and 2 wt % FIrPic has a high gamma light yield of 14 800 Ph/MeV. Incorporating 20-35 wt % hafnium oxide nanoparticles into this organic matrix results in nanocomposites that demonstrate a gamma photopeak energy resolution of 6.4-9.7% at 662 keV while still retaining a high gamma light yield between 8800 and 10 800 Ph/MeV.

Acetylides for the Preparation of Phosphorescent Iridium(III) Complexes: Iridaoxazoles and Their Transformation into Hydroxycarbenes and N,C(sp3),C(sp2),O-Tetradentate Ligands

The preparation of three families of phosphorescent iridium(III) emitters, including iridaoxazole derivatives, hydroxycarbene compounds, and N,C(sp³),C(sp²),O-tetradentate containing complexes, has been performed starting from dimers cis-[Ir(μ²-η²-C≡CR){κ²-C,N-(MeC₆H₃-py)}₂]₂ (R = ^tBu (1a), Ph (1b)). Reactions of 1a with benzamide, acetamide, phenylacetamide, and trifluoroacetamide lead to the iridaoxazole derivatives Ir{κ²-C,O-[C(CH₂^tBu)NC(R)O]}{κ²-C,N-(MeC₆H₃-py)}₂ (R = Ph (2), Me (3), CH₂Ph (4), CF₃ (5)) with a fac disposition of carbons and heteroatoms around the metal center. In 2-methyltetrahydrofuran and dichloromethane, water promotes the C-N rupture of the IrC-N bond of the iridaoxazole ring of 3-5 to form amidate-iridium(III)-hydroxycarbene derivatives Ir{κ¹-N-[NHC(R)O]}{κ²-C,N-(MeC₆H₃-py)}₂{═C(CH₂^tBu)OH} (R = Me (6), CH₂Ph (7), CF₃ (8)). In contrast to 1a, dimer 1b reacts with benzamide and acetamide to give Ir{κ⁴-N,C,C',O-[py-MeC₆H₃-C(CH₂-C₆H₄)NHC(R)O]}{κ²-C,N-(MeC₆H₃-py)}(R = Ph (9), Me (10)), which bear a N,C(sp³),C(sp²),O-tetradentate ligand resulting from a triple coupling (an alkynyl ligand, an amide, and a coordinated aryl group) and a C-H bond activation at the metal coordination sphere. Complexes 2-4 and 6-10 are emissive upon photoexcitation, in orange (2-4), green (6-8), and yellow (9 and 10) regions, with quantum yields between low and moderate (0.01-0.50) and short lifetimes (0.2-9.0 μs).

Phosphorescent [3 + 2 + 1] coordinated Ir(iii) cyano complexes for achieving efficient phosphors and their application in OLED devices

A series of neutral [3 + 2 + 1] coordinated iridium complexes bearing tridentate bis-NHC carbene chelates (2,6-bisimidazolylidene benzene), bidentate chelates (C^N ligands, e.g. derivatives of 2-phenylpridine), and monodentate ions (halides and pseudo-halides, such as Br, I, OCN and CN ions) have been systematically designed and synthesized. X-ray single crystal structure characterization revealed that the nitrogen atom in C^N ligands is located trans to the carbon atom in the benzene ring in tridentate chelates, while the coordinating carbon atom in C^N ligands is located trans to the monodentate ligands. Photophysical studies reveal that the C^N ligands play a vital role in tuning the UV absorption and emission properties, while the tridentate bis-NHC carbene chelates influence the lowest absorption band and emission energy when compared to heteroleptic Ir(ppy)2(acac) [i.e. molar absorptivities at ∼450 nm for ppy-OCN and Ir(ppy)2(acac) are 350 M-1 cm-1 and 1520 M-1 cm-1 and emission maximum peaks are at 465 nm and 515 nm respectively]. Among monodentate ligands that the complexes bear, the group containing the cyanide ligand displays higher emission energy, higher photophysical quantum yields, longer triplet lifetimes and better electrochemical and thermal stabilities than those of cyanate and bromide. Particularly, a blue organic light-emitting diode (OLED) based on dfppy-CN exhibited a maximum external quantum efficiency of 22.94% with CIE coordinates of (0.14, 0.24). Furthermore, a small efficiency roll-off of 5.7% was observed for this device at 1000 cd m-2.

Cleavage of acyclic diaminocarbene ligands at an iridium(iii) center. Recognition of a new reactivity mode for carbene ligands

A new reactivity mode for acyclic diaminocarbene ligands, viz. competitive cleavage of either C–NH₂ or C–NHR bonds in the aminocarbene fragment, is recognized.

The crystal structure of bis-{3,5-di-fluoro-2-[4-(2,4,6-tri-methyl-phen-yl)pyridin-2-yl]phen-yl}(picolinato)iridium(III) and its 4-tert-butyl-pyridin-2-yl analogue

The crystal structures of bis-{3,5-di-fluoro-2-[4-(2,4,6-tri-methyl-phen-yl)pyridin-2-yl]phenyl-κ2 N,C 1}(picolinato-κ2 N,O)iridium(III), [Ir(C20H16F2N)2(C6H4NO2)], 1, and bis-[2-(4-tert-butyl-pyridin-2-yl)-3,5-di-fluoro-phenyl-κ2 N,C 1](picolinato-κ2 N,O)iridium(III), [Ir(C15H14F2N)2(C6H4NO2)], 2, are presented herein. These phospho-rescent cyclo-metallated iridium(III) compounds have been structurally investigated in order to better understand the nature of their blue-shifted emssions while maintaining high quantum yields. Compound 1 exhibits substantial twisting of the mesitylene rings out of the plane of the attached pyridine ring, with dihedral angles of 67.0 (1) and 78.7 (1)° between the best mean planes. For both compounds, the contribution of disordered solvent mol-ecule(s) was removed using the SQUEEZE [Spek (2015 ▸). Acta Cryst. C71, 9-18] routine in PLATON [Spek (2015 ▸). Acta Cryst. C71, 9-18]. These solvent mol-ecules are not considered in the given chemical formula and other crystal data.