Iridium(III) Photocatalysis: A Visible‐Light‐Induced Dearomatizative Tandem [4+2] Cyclization to Furnish Benzindolizidines

A photocatalytic dearomatizative tandem [4+2] cyclization between N‐(2‐iodoethyl)indoles and a variety of alkenes leads to tri‐ and tetracyclic benzindolizidines with high diastereoselectivity and yield. The intermolecular annulation reaction is performed under visible‐light irradiation and employs [Ir(ppy)₃] or [Ir(dtbbpy)(ppy)₂] PF₆ as photocatalysts, in combination with tertiary amines as electron and hydrogen atom donors.     

Regiospecific Intermolecular Aminohydroxylation of Olefins by Photoredox Catalysis

A simple and regiospecific aminohydroxylation of olefins by photoredox catalysis has been developed. N‐protected 1‐aminopyridinium salts are the key compounds and serve as amidyl radical precursors by the action of Ir photocatalysts, fac‐[Ir(ppy)₃] and [Ir(ppy)₂(dtbbpy)](PF₆) (ppy=2‐pyridylphenyl, dtbbpy=4,4′‐di‐tert‐butyl‐2,2′‐bipyridine). The present photocatalytic system allows for synthesis of vicinal aminoalcohol derivatives from olefins with various functional groups under mild reaction conditions with easy handling.     

Electrochemiluminescence Studies of Phosphorescent Dopant and Host Molecules of Polymer Light-emitting Diodes

Electrochemiluminescence (ECL) from tris(2‐phenylpyridine)irdium [Ir(ppy)₃] was investigated following cross reaction of its anion with oxidized poly(N‐vinyl‐carbazole) (PVK) and its cation with reduced 2‐(4‐biphenylyl)‐5‐(4‐tert‐butyl‐phenyl)‐1,3,4‐oxadiazole (PBD). Both cross reactions show Ir(ppy)₃ emission and the cross reaction of PVK^+·/Ir(ppy)⁻₃ showed the highest ECL intensity. The comparisons of the reaction enthalpy and the energy of Ir(ppy)₃ light emitting shows that reaction between PVK^+· and Ir(ppy)⁻₃ is energy sufficient to populate metal‐to‐ligand charge transfer (MLCT) excited singlet (3.04 eV) of Ir(ppy)₃, while the reaction between Ir(ppy)⁺₃ and PBD^{− ·} is energy efficient to populate MLCT excited triplet (2.4 eV). The ECL result in solution reveals that the energy released from charge transfer between the Ir(ppy)₃ and PVK or PBD is sufficient to produce the excited state of Ir(ppy)₃ in solid polymer light‐emitting diodes (PLEDs) based on PVK:PBD hosts doped by Ir(ppy)₃. These results obtained will provide further insight into charge‐transfer excitation in PLEDs.     

Synthesis of fac‐Ir(ppy)3 end‐functionalized poly(1,3‐cyclohexadiene): single monomer addition of fac‐Ir(ppy)2(vppy) for well‐controlled polymer synthesis

Synthesis of the polymer whose end is functionalized by fac‐Ir(ppy)₃ (ppy = 2‐phenylpyridyl) was achieved by using (living) anionic polymerization of 1,3‐cyclohexadiene: the reaction of poly(1,3‐cyclohexadienyl)lithium (PCHDLi) with fac‐Ir(ppy)₂(vppy) [vppy = 2‐(4‐vinylphenyl)pyridyl] resulted in nucleophilic attack of the carbanion in PCHDLi on the vinyl group of fac‐Ir(ppy)₂(vppy) selectively. Complexation of the pyridyl ring protected the α‐carbons of fac‐Ir(ppy)₂(vppy) from the reaction of the anionic polymer. The homopolymerization of fac‐Ir(ppy)₂(vppy) did not occur, and only one molecule of fac‐Ir(ppy)₂(vppy) reacted with the carbanion of PCHDLi and was selectively incorporated into an end of poly(1,3‐cyclohexadiene) (PCHD). Thus, the PCHD with fac‐Ir(ppy)₃ end‐group was obtained with a well‐controlled and defined polymer structure and molecular weight. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Theoretical design of phosphorescence parameters for organic electro-luminescence devices based on iridium complexes

Time-dependent density functional theory with quadratic response methodology is used in order to calculate and compare spin–orbit coupling effects and the main mechanism of phosphorescence of the neutral Ir(ppy)₃ and cationic [Ir(bpy)₃]³⁺ tris-iridium compounds, [Ir(ppy)₂(bpy)]⁺ and [Ir(2-phenylpyridine)₂(4,4′-tert-butyl-2,2′-bipyridine]⁺ complexes, including also the recently synthesised [Ir(2-phenylpyridine)₂(4,4′-dimethylamino-2,2′-bipyridine]⁺ and [Ir(2,4-difluorophenylpyridine)₂(4,4′-dimethylamino-2,2′-bipyridine]⁺ dyes, where ppy = 2-phenylpyridine and bpy = 2,2′-bipyridine ligands. Comparison with the symmetric, lighter and more studied [Ru(bpy)₃]²⁺ and [Rh(bpy)₃]³⁺ complexes is also presented. Variations in phosphorescence lifetimes for Ir(ppy)₃ and [Ir(bpy)₃]³⁺ dyes as well as for the mixed cationic complexes are well reproduced by the quadratic response method. All the ortho-metalated iridium compounds exhibit strong phosphorescence, which is used in organic light-emitting diodes (OLEDs) to overcome the efficiency limit imposed by the formation of triplet excitons. The results from the first principle theoretical analysis of phosphorescence have helped to clarify the connections between the main features of electronic structure and the photo-physical properties of the studied heavy organometallic OLED materials.     

Triplet Energy Transfer from Ruthenium Complexes to Chiral Eniminium Ions: Enantioselective Synthesis of Cyclobutanecarbaldehydes by [2+2] Photocycloaddition

Chiral eniminium salts, prepared from α,β‐unsaturated aldehydes and a chiral proline derived secondary amine, underwent, upon irradiation with visible light, a ruthenium‐catalyzed (2.5 mol %) intermolecular [2+2] photocycloaddition to olefins, which after hydrolysis led to chiral cyclobutanecarbaldehydes (17 examples, 49–74 % yield), with high diastereo‐ and enantioselectivities. Ru(bpz)₃(PF₆)₂ was utilized as the ruthenium catalyst and laser flash photolysis studies show that the catalyst operates exclusively by triplet‐energy transfer (sensitization). A catalytic system was devised with a chiral secondary amine co‐catalyst. In the catalytic reactions, Ru(bpy)₃(PF₆)₂ was employed, and laser flash photolysis experiments suggest it undergoes both electron and energy transfer. However, experimental evidence supports the hypothesis that energy transfer is the only productive quenching mechanism. Control experiments using Ir(ppy)₃ showed no catalysis for the intermolecular [2+2] photocycloaddition of an eniminium ion.     

Robust Tris‐Cyclometalated Iridium(III) Phosphors with Ligands for Effective Charge Carrier Injection/Transport: Synthesis,Redox, Photophysical,and Electrophosphorescent Behavior

With the target to design and develop new functionalized green triplet light emitters that possess distinctive electronic properties for robust and highly efficient phosphorescent organic light‐emitting diodes (PHOLEDs), a series of bluish–green to yellow–green phosphorescent tris‐cyclometalated homoleptic iridium(III) complexes [Ir(ppy‐X)₃] (X=SiPh₃, GePh₃, NPh₂, POPh₂, OPh, SPh, SO₂Ph, Hppy=2‐phenylpyridine) have been synthesized and fully characterized by spectroscopic, redox, and photophysical methods. By chemically manipulating the lowest triplet‐state character of Ir(ppy)₃ with some functional main‐group 14–16 moieties on the phenyl ring of ppy, a new family of metallophosphors with high‐emission quantum yields, short triplet‐state lifetimes, and good hole‐injection/hole‐transporting or electron‐injection/electron‐transporting properties can be obtained. Remarkably, all of these Ir^III complexes show outstanding electrophosphorescent performance in multilayer doped devices that surpass that of the state‐of‐the‐art green‐emitting dopant Ir(ppy)₃. The devices described herein can reach the maximum external quantum efficiency (η_ext) of 12.3 %, luminance efficiency (η_L) of 50.8 cd A^?1, power efficiency (η_p) of 36.9 Lm W^?1 for [Ir(ppy‐SiPh₃)₃], 13.9 %, 60.8 cd A^?1, 49.1 Lm W^?1 for [Ir(ppy‐NPh₂)₃], and 10.1 %, 37.6 cd A^?1, 26.1 Lm W^?1 for [Ir(ppy‐SO₂Ph)₃]. These results provide a completely new and effective strategy for carrier injection into the electrophosphor to afford high‐performance PHOLEDs suitable for various display applications.     

Long‐Lived Room‐Temperature Deep‐Red‐Emissive Intraligand Triplet Excited State of Naphthalimide in Cyclometalated IrIII Complexes and its Application in Triplet‐Triplet Annihilation‐Based Upconversion

Cyclometalated Ir^III complexes with acetylide ppy and bpy ligands were prepared (ppy=2‐phenylpyridine, bpy=2,2′‐bipyridine) in which naphthal ( Ir‐2 ) and naphthalimide (NI) were attached onto the ppy ( Ir‐3 ) and bpy ligands ( Ir‐4 ) through acetylide bonds. [Ir(ppy)₃] ( Ir‐1 ) was also prepared as a model complex. Room‐temperature phosphorescence was observed for the complexes; both neutral and cationic complexes Ir‐3 and Ir‐4 showed strong absorption in the visible range (ε=39600 M ^?1 cm^?1 at 402 nm and ε=25100 M ^?1 cm^?1 at 404 nm, respectively), long‐lived triplet excited states (τ_T=9.30 μs and 16.45 μs) and room‐temperature red emission (λ_em=640 nm, Φ_p=1.4 % and λ_em=627 nm, Φ_p=0.3 %; cf. Ir‐1 : ε=16600 M ^?1 cm^?1 at 382 nm, τ_em=1.16 μs, Φ_p=72.6 %). Ir‐3 was strongly phosphorescent in non‐polar solvent (i.e., toluene), but the emission was completely quenched in polar solvents (MeCN). Ir‐4 gave an opposite response to the solvent polarity, that is, stronger phosphorescence in polar solvents than in non‐polar solvents. Emission of Ir‐1 and Ir‐2 was not solvent‐polarity‐dependent. The T₁ excited states of Ir‐2 , Ir‐3 , and Ir‐4 were identified as mainly intraligand triplet excited states (³IL) by their small thermally induced Stokes shifts (ΔE_s), nanosecond time‐resolved transient difference absorption spectroscopy, and spin‐density analysis. The complexes were used as triplet photosensitizers for triplet‐triplet annihilation (TTA) upconversion and quantum yields of 7.1 % and 14.4 % were observed for Ir‐2 and Ir‐3 , respectively, whereas the upconversion was negligible for Ir‐1 and Ir‐4 . These results will be useful for designing visible‐light‐harvesting transition‐metal complexes and for their applications as triplet photosensitizers for photocatalysis, photovoltaics, TTA upconversion, etc.     

Striking Differences in Properties of Geometric Isomers of [Ir(tpy)(ppy)H]+: Experimental and Computational Studies of their Hydricities,Interaction with CO2, and Photochemistry

We prepared two geometric isomers of [Ir(tpy)(ppy)H]⁺, previously proposed as a key intermediate in the photochemical reduction of CO₂ to CO, and characterized their notably different ground‐ and excited‐state interactions with CO₂ and their hydricities using experimental and computational methods. Only one isomer, C‐trans‐[Ir(tpy)(ppy)H]⁺, reacts with CO₂ to generate the formato complex in the ground state, consistent with its calculated hydricity. Under photocatalytic conditions in CH₃CN/TEOA, a common reactive C‐trans‐[Ir(tpy)(ppy)]⁰ species, irrespective of the starting isomer or monodentate ligand (such as hydride or Cl), reacts with CO₂ and produces CO with the same catalytic efficiency.     

Triplet level-dependent photoluminescence and photoconduction properties of π-conjugated polymer thin films doped by iridium complexes

Triplet energy level-dependent decay pathways of excitons populated on iridium (Ir) complexes within π-conjugated polymeric matrices were studied by means of photoluminescence (PL) and photoconduction action spectroscopy. We chose a set of matrices, poly(9-vinylcarbazole) (PVK), poly[9,9-bis(2-ethylhexyl)fluorene-2,7-diyl] (PF2/6), poly [2-(5′-cyano-5′-methyl-hexyloxy)-1,4-phenylene] (CNPPP), and poly [2-(5′-cyano-5′-methyl-hexyloxy)-1,4-phenylene-co-pridine] (CNPPP-py10 and CNPPP-Py20), having triplet energy levels ranging from 2.2 up to 3.0 eV. As Ir-complex dopants, we selected three phosphorescent emitters, iridium(III)bis(2-(2′-benzothienyl) pyridinato-N-acetylacetonate) (Ir(btp)₂acac), iridium(III)fac-tris(2-phenylpyridine) (Ir(ppy)₃), and iridium(III)bis[(4,6-fluorophenyl)-pyridinato-N,C^2′]picolinate (FIrpic), having triplet energy levels of 2.1, 2.5, and 2.7 eV, respectively. It was found that the triplet emission from the dopants, being populated via energy transfer from the matrices, was strongly dependent on the matching of triplet energy levels between matrix polymers and Ir-complexes. Photocurrent action spectra confirm effective exciton confinement at the dopants sites in the case of PVK matrix systems.     

Striking Differences in Properties of Geometric Isomers of [Ir(tpy)(ppy)H]+: Experimental and Computational Studies of their Hydricities,Interaction with CO2, and Photochemistry

We prepared two geometric isomers of [Ir(tpy)(ppy)H]⁺, previously proposed as a key intermediate in the photochemical reduction of CO₂ to CO, and characterized their notably different ground‐ and excited‐state interactions with CO₂ and their hydricities using experimental and computational methods. Only one isomer, C‐trans‐[Ir(tpy)(ppy)H]⁺, reacts with CO₂ to generate the formato complex in the ground state, consistent with its calculated hydricity. Under photocatalytic conditions in CH₃CN/TEOA, a common reactive C‐trans‐[Ir(tpy)(ppy)]⁰ species, irrespective of the starting isomer or monodentate ligand (such as hydride or Cl), reacts with CO₂ and produces CO with the same catalytic efficiency.     

Enhanced Electrochemiluminescence from a Stoichiometric Ruthenium(II)–Iridium(III) Complex Soft Salt

Electrochemiluminescence (ECL) and electrochemistry are reported for a heterometallic soft salt, [Ru(dtbubpy)₃][Ir(ppy)₂(CN)₂]₂ ( [Ir][Ru][Ir] ), consisting of a 2:1 ratio of complementary charged Ru and Ir complexes possessing two different emission colors. The [Ru]²⁺ and [Ir]^? moieties in the [Ir][Ru][Ir] greatly reduce the energy required to produce ECL. Though ECL intensity in the annihilation path was enhanced 18× relative to that of [Ru(bpy)₃]²⁺, ECL in the co‐reactant path with tri‐n‐propylamine was enhanced a further 4×. Spooling spectroscopy gives insight into ECL mechanisms: the unique light emission at 634 nm is due to the [Ru]²⁺* excited state and no [Ir]^?* was generated in either route. Overall, the soft salt system is anticipated to be attractive and suitable for the development of efficient and low‐energy‐cost ECL detection systems.     

Understanding Electrogenerated Chemiluminescence Efficiency in Blue‐Shifted Iridium(III)‐Complexes: An Experimental and Theoretical Study

Compared to tris(2‐phenylpyridine)iridium(III) ([Ir(ppy)₃]), iridium(III) complexes containing difluorophenylpyridine (df‐ppy) and/or an ancillary triazolylpyridine ligand [3‐phenyl‐1,2,4‐triazol‐5‐ylpyridinato (ptp) or 1‐benzyl‐1,2,3‐triazol‐4‐ylpyridine (ptb)] exhibit considerable hypsochromic shifts (ca. 25–60 nm), due to the significant stabilising effect of these ligands on the HOMO energy, whilst having relatively little effect on the LUMO. Despite their lower photoluminescence quantum yields compared with [Ir(ppy)₃] and [Ir(df‐ppy)₃], the iridium(III) complexes containing triazolylpyridine ligands gave greater electrogenerated chemiluminescence (ECL) intensities (using tri‐n‐propylamine (TPA) as a co‐reactant), which can in part be ascribed to the more energetically favourable reactions of the oxidised complex (M⁺) with both TPA and its neutral radical oxidation product. The calculated iridium(III) complex LUMO energies were shown to be a good predictor of the corresponding M⁺ LUMO energies, and both HOMO and LUMO levels are related to ECL efficiency. The theoretical and experimental data together show that the best strategy for the design of efficient new blue‐shifted electrochemiluminophores is to aim to stabilise the HOMO, while only moderately stabilising the LUMO, thereby increasing the energy gap but ensuring favourable thermodynamics and kinetics for the ECL reaction. Of the iridium(III) complexes examined, [Ir(df‐ppy)₂(ptb)]⁺ was most attractive as a blue‐emitter for ECL detection, featuring a large hypsochromic shift (λ_max=454 and 484 nm), superior co‐reactant ECL intensity than the archetypal homoleptic green and blue emitters: [Ir(ppy)₃] and [Ir(df‐ppy)₃] (by over 16‐fold and threefold, respectively), and greater solubility in polar solvents.     

Helicenes as All‐in‐One Organic Materials for Application in OLEDs: Synthesis and Diverse Applications of Carbo‐ and Aza[5]helical Diamines

A set of eight helical diamines were designed and synthesized to demonstrate their relevance as all‐in‐one materials for multifarious applications in organic light‐emitting diodes (OLEDs), that is, as hole‐transporting materials (HTMs), EMs, bifunctional hole transporting + emissive materials, and host materials. Azahelical diamines function very well as HTMs. Indeed, with high T_g values (127–214 °C), they are superior alternatives to popular N,N′‐di(1‐naphthyl)‐N,N′‐diphenyl‐(1,1′‐biphenyl)‐4,4′‐diamine (NPB). All the helical diamines exhibit emissive properties when employed in nondoped as well as doped devices, the performance characteristics being superior in the latter. One of the carbohelical diamines (CHTPA) serves the dual function of hole transport as well as emission in simple double‐layer devices; the efficiencies observed were better by quite some margin than those of other emissive helicenes reported. The twisting endows helical diamines with significantly high triplet energies such that they also function as host materials for red and green phosphors, that is, [Ir(btp)₂acac] (btp=2‐(2′‐benzothienyl)pyridine; acac=acetylacetonate) and [Ir(ppy)₃] (ppy=2‐phenylpyridine), respectively. The results of device fabrications demonstrate how helicity/ helical scaffold may be diligently exploited to create molecular systems for maneuvering diverse applications in OLEDs.     

Synthesis and properties of iridium polymer complexes based on novel bipyridyl ligands

A novel monomer, viz., bipyridyl-containing dicarboxylic acid, was synthesized from 6-pyridyl-3,4-pyridine dicarboxylic acid anhydride and 5-aminoisophthalic acid. Novel polymer macroligands, viz., copolyamides containing 5, 15, 30, and 45% of the bipyridyl side groups, were obtained based on this monomer by low-temperature polycondensation. Metal polymer complexes (MPC) with different Ir(ppy)₂ content were synthesized by the reaction of the polymer ligand with the binuclear complex [Ir(ppy)₂Cl]₂ (ppy is 2-phenylpyridine) and their properties were studied.     

Cyclometalated Ir(III) complexes containing N-aryl picolinamide ancillary ligands

The reaction of the cyclometalated chloro-bridged iridium(III) dimer, [(ppy)₂ Ir(μ-Cl)]₂ (ppy - 2-phenyl pyridine) with N-aryl picolinamides (LH, LH-NO₂, LH-CH₃, LH-l, LH-F) resulted in the formation of neutral heteroleptic complexes [Ir(ppy)₂L] (1), [Ir(ppy)₂L-NO₂](2), [Ir(ppy)₂L-CH₃](3), [Ir(ppy)₂L-Cl](4) and [Ir(ppy)₂L-F] (5). These complexes contain a six-coordinate iridium with a 2C, 4N coordination environment. The N-aryl picolinamide ligands are deprotonated during complexation and the resulting amidates bind to iridium in a chelating manner (N, N). Optical spectroscopic studies revealed that the complexes 1-5 exhibited intense π→π^∗ absorptions in the ultraviolet region. In addition low energy transitions due to ¹MLCT, ¹LLCT and ³MLCT are also seen. The emission spectra of 1-5, upon excitation at 450 nm, show a single emission with a λ_max around 513 nm. The lifetimes of this emission are in between 7.4 and 9.6 μs while the quantum yields are quite high and range from 0.2 to 0.5. Based on density functional theory (DFT) calculations on 1 and 3, the three highest occupied orbitals are composed of ligand π orbitals mixed with Ir-d orbitals while the three lowest unoccupied orbitals are mostly π orbitals of the ligands. From the time dependent DFT calculations it is revealed that the lowest energy electronic singlet and triplet excitations are a mixture of MLCT and LLCT.     

Iridium(III) Complex-Based Activatable Probe for Phosphorescent/Time-Gated Luminescent Sensing and Imaging of Cysteine in Mitochondria of Live Cells and Animals

This study reports an activatable iridium(III) complex probe for phosphorescence/time-gated luminescence detection of cysteine (Cys) in vitro and in vivo. The probe, [Ir(ppy)₂(NTY-bpy)](PF₆) [ppy: 2-phenylpyridine; NTY-bpy: 4-methyl-4′-(2-nitrovinyl)-2,2′-bipyridine], is developed by incorporating a strong electron-withdrawing group, nitroolefin, into a bipyridine ligand of the Ir^III complex. The luminescence of the probe is quenched owing to the intramolecular charge transfer (ICT) process, but switched on by a specific recognition reaction between the probe and Cys. [Ir(ppy)₂(NTY-bpy)](PF₆) shows high sensitivity and selectivity for Cys detection and good biocompatibility. The long-lived emission of [Ir(ppy)₂(NTY-bpy)](PF₆) allows time-gated luminescence analysis of Cys in cells and human sera. These properties make it convenient for the phosphorescence and time-gated luminescence imaging and flow cytometry analysis of Cys in live samples. The Cys images in cancer cells and inflamed macrophage cells reveal that [Ir(ppy)₂(NTY-bpy)](PF₆) is distributed in mitochondria after cellular internalization. Visualizations and flow cytometry analysis of mitochondrial Cys levels and Cys-mediated redox activities of live cells are achieved. By using [Ir(ppy)₂(NTY-bpy)](PF₆) as a probe, in vivo sensing and imaging of Cys in D. magna, zebrafish, and mice are then demonstrated.     

Highly phosphorescent iridium complexes containing both tridentate bis(benzimidazolyl)-benzene or -pyridine and bidentate phenylpyridine: synthesis, photophysical properties, and theoretical study of Ir-bis(benzimidazolyl)benzene complex

Novel mixed-ligand Ir(III) complexes, [Ir(L)(NwedgeC)X]n+ (L = N/\C/\N or N/\N/\N; X = Cl, Br, I, CN, CH3CN, or -CCPh; n = 0 or 1), were synthesized, where N/\CwedgeN = bis(N-methylbenzimidazolyl)benzene (Mebib) and bis(N-phenylbenzimidazolyl)benzene (Phbib), N/\N/\N = bis(N-methylbenzimidazolyl)pyridine (Mebip), and N/\C = phenylpyridine (ppy) derivatives. The X-ray crystal structures of [Ir(Phbib)(ppy)Cl] and [Ir(Mebib)(mppy)Cl] [mppy = 5-methyl-2-(2'-pyridyl)phenyl] indicate that the nitrogen atom of the ppy ligand is located trans to the coordinating carbon atom in Me- or Phbib, while the coordinating carbon atom in ppy occupies the trans position of Cl. [Ir(Mebip)(ppy)Cl]+ showed a quasireversible Ir(III/IV) oxidation wave at +1.05 V, while the Ir complexes, [Ir(Mebib)(ppy)Cl], were oxidized at +0.42 V versus Fc/Fc+. The introduction of an Ir-C bond in [Ir(Mebib)(ppy)Cl] induces a large potential shift of 0.63 V in a negative direction. Further, the oxidation potential of [Ir(Mebib)(Rppy)X] was altered by the substitution of R, R', and X groups. Compared to the oxidation potential, the first reduction potential revealed an almost constant value at -2.36 to -2.46 V for [Ir(L)(ppy)Cl] (L = Mebib and Phbib) and -1.52 V for [Ir(Mebip)(ppy)Cl. The UV-vis spectra of [Ir(Mebib)(R-ppy)X] show a clear singlet metal-to-ligand charge-transfer transition around 407 approximately 425 nm and a triplet metal-to-ligand charge-transfer transition at 498 approximately 523 nm. [Ir(Mebip)(ppy)Cl]+ emits at 610 nm with a luminescent quantum yield of Phi = 0.16 at room temperature. The phosphorescence of [Ir(Mebib)(ppy)X] was observed at 526 nm for X = CN and 555 nm for X = Cl with the high luminescent quantum yields, Phi = 0.77 approximately 0.86, at room temperature. [Ir(Phbib)(ppy)Cl] shows the emission at 559 nm with a luminescent quantum yield of Phi = 0.95, which is an unprecedentedly high value compared to those of other emissive metal complexes. Compared to the luminescent quantum yields of the Ir(ppy)2(L) derivatives and [Ir(Mebip)(ppy)Cl]+, the neutral Ir complexes, [Ir(L)(R-ppy)X] (L = Me- or Phbib), reveal very high quantum yields and large radiative rate constants (kr) ranging from 3.4 x 10(5) to 5.5 x 10(5) s(-1). The density functional theory calculation suggests that these Ir complexes possess dominantly metal-to-ligand charge-transfer and halide-to-ligand charge-transfer excited states. The mechanism for a high phosphorescence yield in [Ir(bib)(ppy)X] is discussed herein from the perspective of the theoretical consideration of radiative rate constants using perturbation theory and a one-center spin-orbit coupling approximation.     

IrIII and RuII Complexes Containing Triazole‐Pyridine Ligands: Luminescence Enhancement upon Substitution with β‐Cyclodextrin

Novel 2‐(1‐substituted‐1H‐1,2,3‐triazol‐4‐yl)pyridine (pytl) ligands have been prepared by “click chemistry” and used in the preparation of heteroleptic complexes of Ru and Ir with bipyridine (bpy) and phenylpyridine (ppy) ligands, respectively, resulting in [Ru(bpy)₂(pytl‐R)]Cl₂ and [Ir(ppy)₂(pytl‐R)]Cl (R=methyl, adamantane (ada), β‐cyclodextrin (βCD)). The two diastereoisomers of the Ir complex with the appended β‐cyclodextrin, [Ir(ppy)₂(pytl‐βCD)]Cl, were separated. The [Ru(bpy)₂(pytl‐R)]Cl₂ (R=Me, ada or βCD) complexes have lower lifetimes and quantum yields than other polypyridine complexes. In contrast, the cyclometalated Ir complexes display rather long lifetimes and very high emission quantum yields. The emission quantum yield and lifetime (Φ=0.23, τ=1000 ns) of [Ir(ppy)₂(pytl‐ada)]Cl are surprisingly enhanced in [Ir(ppy)₂(pytl‐βCD)]Cl (Φ=0.54, τ=2800 ns). This behavior is unprecedented for a metal complex and is most likely due to its increased rigidity and protection from water molecules as well as from dioxygen quenching, because of the hydrophobic cavity of the βCD covalently attached to pytl. The emissive excited state is localized on these cyclometalating ligands, as underlined by the shift to the blue (450 nm) upon substitution with two electron‐withdrawing fluorine substituents on the phenyl unit. The significant differences between the quantum yields of the two separate diastereoisomers of [Ir(ppy)₂(pytl‐βCD)]Cl (0.49 vs. 0.70) are attributed to different interactions of the chiral cyclodextrin substituent with the Δ and Λ isomers of the metal complex.     

Photoredox mediated annelation of iododifluoromethylated alcohols with 1,1-diarylethylenes

A method for the synthesis of 3,3-difluorotetrahydrofurans from iododifluoromethylated alcohols and 1,1-diarylethylenes is described. The reaction is performed under irradiation with 400?nm light emitting diodes in the presence of a cationic iridium(III) photocatalyst, [Ir(ppy)₂(dtbbpy)]PF₆, substoichiometric amounts of triphenylphosphine and sodium trifluoroacetate as a base.