Highly selective phosphorescent chemosensor for fluoride based on an iridium(III) complex containing arylborane units

A new phosphorescent iridium(III) complex [Ir(Bpq)2(bpy)](+)PF6(-) based on cyclometalated ligands (Bpq) containing a dimesitylboryl group was synthesized and characterized by photophysical and electrochemical studies. The excited-state properties of Bpq and [Ir(Bpq)2(bpy)](+)PF6(-) were investigated using molecular orbital calculations. Importantly, both Bpq and [Ir(Bpq)2(bpy)](+)PF6(-) could be used as highly selective chemosensors for a fluoride anion (F(-)) detected by the naked eye, owing to the interaction of the dimesitylboryl group (BMes2) with F(-). For the Bpq ligand, a red shift of the emission spectrum was observed upon the addition of F(-), which could be attributed to an excited-state switch from a pi-pi* transition to a charge-transfer transition upon complexation with F(-). The addition of F(-) to a solution of [Ir(Bpq)2(bpy)](+)PF6(-) induced a change in the solution color from yellow to orange-red and phosphorescent quenching, indicating that [Ir(Bpq)2(bpy)](+)PF6(-) could act as an excellent ON-OFF-type phosphorescent chemosensor for F(-).     

Ratiometric phosphorescence imaging of Hg(II) in living cells based on a neutral iridium(III) complex

In this work, a neutral iridium(III) complex [Ir(bt)(2)(acac)] (Hbt = 2-phenylbenzothiazole; Hacac = acetylacetone) has been realized as a Hg(II)-selective sensor through UV-vis absorption, phosphorescence emission, and electrochemical measurements and was further developed as a phosphorescent agent for monitoring intracellular Hg(II). Upon addition of Hg(II) to a solution of [Ir(bt)(2)(acac)], a noticeable spectral blue shift in both absorption and phosphorescent emission bands was measured. (1)H NMR spectroscopic titration experiments indicated that coordination of Hg(II) to the complex induces fast decomposition of [Ir(bt)(2)(acac)] to form a new complex, which is responsible for the significant variations in optical and electrochemical signals. Importantly, cell imaging experiments have shown that [Ir(bt)(2)(acac)] is membrane permeable and can be used to monitor the changes in Hg(II) levels within cells in a ratiometric phosphorescence mode.     

Blue phosphorescence from mixed cyano-isocyanide cyclometalated iridium(III) complexes

The synthesis, structure, and photophysical and electrochemical properties of cyclometalated iridium complexes with ancillary cyano and isocyanide ligands are described. In the first synthetic step, cleavage of dichloro-bridged dimers [Ir(N=C)2(mu-Cl)]2 (N=C = 2-phenylpyridine, 2-(2-fluorophenyl)pyridine, and 2-(2,4-difluorophenyl)pyridine) by isocyanide ligands gave monomeric species of the types Ir(N=C)2(RNC)(Cl) (RNC = t-butyl isocyanide, 1,1,3,3-tetramethylbutyl isocyanide, 2-morpholinoethyl isocyanide, and 2,6-dimethylphenyl isocyanide). In turn, the chloride was replaced by cyanide giving Ir(N=C)2(RNC)(CN). The X-ray structures for two of the complexes show that the trans-pyridyl/cis-phenyl geometry of the parent dimer is preserved, with the ancillary ligands positioned trans to the cyclometalated phenyls. The cyano complexes all display strong blue photoluminescence in ambient, deoxygenated solutions with the first lambdamax ranging from 441 to 458 nm, quantum yields spanning 0.60 to 0.75, and luminescent lifetimes of 12.0-21.4 mus. A lack of solvatochromism and highly structured emission indicate that the lowest energy excited state is triplet ligand centered with some admixture of singlet metal-to-ligand charge-transfer character.     

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.     

Bright blue phosphorescence from cationic bis-cyclometalated iridium(III) isocyanide complexes

We report new bis-cyclometalated cationic iridium(III) complexes [(C(^)N)(2)Ir(CN-tert-Bu)(2)](CF(3)SO(3)) that have tert-butyl isocyanides as neutral auxiliary ligands and 2-phenylpyridine or 2-(4'-fluorophenyl)-R-pyridines (where R is 4-methoxy, 4-tert-butyl, or5-trifluoromethyl) as C(^)N ligands. The complexes are white or pale yellow solids that show irreversible reduction and oxidation processes and have a large electrochemical gap of 3.58-3.83 V. They emit blue or blue-green phosphorescence in liquid/solid solutions from a cyclometalating-ligand-centered excited state. Their emission spectra show vibronic structure with the highest-energy luminescence peak at 440-459 nm. The corresponding quantum yields and observed excited-state lifetimes are up to 76% and 46 μs, respectively, and the calculated radiative lifetimes are in the range of 46-82 μs. In solution, the photophysical properties of the complexes are solvent-independent, and their emission color is tuned by variation of the substituents in the cyclometalating ligand. For most of the complexes, an emission color red shift occurs in going from solution to neat solids. However, the shift is minimal for the complexes with bulky tert-butyl or trifluoromethyl groups on the cyclometalating ligands that prevent aggregation. We report the first example of an iridium(III) isocyanide complex that emits blue phosphorescence not only in solution but also as a neat solid.     

A bright tetranuclear iridium(III) complex

A cyclic tetranuclear cyclometallated iridium(III) complex using cyanide anions as bridging ligands and displaying a tetrahedrally distorted square geometry has been obtained with high yield; photo- and electrochemical characterizations show that most interesting properties of mononuclear cyclometallated iridium complexes are retained in the tetranuclear assembly.     

A cyclometallated iridium(III) dimethylphenylphosphine complex

[Ir(cod)Cl]₂ (cod = 1,5-cyclooctadiene) reacts with PMe₂Ph in CH₃CN to give the red cation [Ir(PMe₂Ph)₄]⁺. This complex in CH₃CN reacts with H₂ to give cis-[IrH₂(PMe₂Ph)₄]⁺, but on reflux for 6 h in the absence of H₂, it gives the first example of a cyclometallated PMe₂Ph complex fac-[IrH(PMe₂C₆H₄)(PMe₂Ph)₃]⁺, as shown by PMR spectroscopy and preliminary X-ray crystallographic data.     

Effects of fluorination on iridium(III) complex phosphorescence: magnetic circular dichroism and relativistic time-dependent density functional theory

We use a combination of low temperature, high field magnetic circular dichroism, absorption, and emission spectroscopy with relativistic time-dependent density functional calculations to reveal a subtle interplay between the effects of chemical substitution and spin-orbit coupling (SOC) in a family of iridium(III) complexes. Fluorination at the ortho and para positions of the phenyl group of fac-tris(1-methyl-5-phenyl-3-n-propyl-[1,2,4]triazolyl)iridium(III) cause changes that are independent of whether the other position is fluorinated or protonated. This is demonstrated by a simple linear relationship found for a range of measured and calculated properties of these complexes. Further, we show that the phosphorescent radiative rate, k(r), is determined by the degree to which SOC is able to hybridize T(1) to S(3) and that k(r) is proportional to the inverse fourth power of the energy gap between these excitations. We show that fluorination in the para position leads to a much larger increase of the energy gap than fluorination at the ortho position. Theory is used to trace this back to the fact that fluorination at the para position increases the difference in electron density between the phenyl and triazolyl groups, which distorts the complex further from octahedral symmetry, and increases the energy separation between the highest occupied molecular orbital (HOMO) and the HOMO-1. This provides a new design criterion for phosphorescent iridium(III) complexes for organic optoelectronic applications. In contrast, the nonradiative rate is greatly enhanced by fluorination at the ortho position. This may be connected to a significant redistribution of spectral weight. We also show that the lowest energy excitation, 1A, has almost no oscillator strength; therefore, the second lowest excitation, 2E, is the dominant emissive state at room temperature. Nevertheless the mirror image rule between absorption and emission is obeyed, as 2E is responsible for both absorption and emission at all but very low (<10 K) temperatures.     

Cationic iridium(III) complexes for phosphorescence staining in the cytoplasm of living cells

Two cationic iridium(III) complexes with bright green and red emissions were demonstrated as phosphorescent dyes for living cell imaging. In particular, their exclusive staining in cytoplasm, low cytotoxicity and reduced photobleaching, as well as cell membrane permeability, make the two complexes promising candidates for the design of specific bioimaging agents.     

Multisignaling detection of Hg2+ based on a phosphorescent iridium(III) complex

A multisignaling chemosensor for Hg(2+) based on the iridium(III) complex Ir(thq)(2)(acac) was realized through UV-Vis absorption, phosphorescent emission and electrochemical measurements. Upon addition of Hg(2+), an obvious blue-shift in absorption spectra and a strong decrease of emission intensity were measured for Ir(thq)(2)(acac), which could be observed by the naked eye. Hg(2+) is coordinated to Ir(thq)(2)(acac), forming a 1 : 1 complex. Because Hg(2+) is a thiophilic metal ion, the interaction between Hg(2+) and the sulfur atom of cyclometalated ligands is responsible for the significant variations in optical and electrochemical signals.     

Design and synthesis of iridium(III) azacrown complex: application as a highly sensitive metal cation phosphorescence sensor

A new metal cation probe bearing a central Ir(III) element and 1-aza-15-crown-5-ether substituted pyridyl pyrazolate as the chelate was synthesized. The octahedral molecular structure of was confirmed using single crystal X-ray diffraction analyses. Subsequent photophysical study showed yellow-green emission at approximately 560 nm in both fluid solution and solid state at room temperature. Remarkable differentiation in spectral properties upon metal cation (e.g. Ca2+) complexation makes complex a highly sensitive phosphorescence probe.     

Solid-state electrochemiluminescence of a novel iridium（Ⅲ） complex

The solid-state ECL behavior of a water-insoluble bis-cyclometalated （pq）2Ir（N-phMA） complex is presented, in which pq is a 2-phenylquinoline anion and N-phMA is N-phenyl methacrylamide, a monoanionic bidentate ligand. The MWNTs/（pq）2Ir（N-phMA） film, MWNTs/Ru（bpy）3^2＋ film and （pq）2Ir（N-phMA） directly modified glassy carbon electrode were fabricated; only the MWNTs/（pq）2Ir（N-phMA） film can produce steady ECL in the presence of tri-n-propylamine as a coreactant.     

Influence of aggregation on the phosphorescence of iridium complex in poly(methyl methacrylate) matrix

In this study, novel phosphorescent compound of iridium(III)bis(2,3‐diphenylquinoxaline)2‐(benzoimidazol‐2‐yl)pyridine (IrQB) was prepared and the emission study suggests the solid form of IrQB has less phosphorescence intensity than its solution in tetrahydrofuran (THF). To avoid the potential aggregation of IrQB in the concentrated state, poly(methyl methacrylate) (PMMA) was intentionally added as isolator to make solutions of different concentrations in THF and then solid films of IrQB/PMMA of different compositions after THF removal. Films of IrQB/PMMA prepared from dilute solutions exhibit two emission bands centered at 540 and 640 nm, respectively, which is in contrast to the sole 640‐nm emission band observed for films prepared from semidilute solutions. The 540‐ and 640‐nm bands show progressive variations of the intensity with temperature. Emission band at 540 nm is derived from the polarized optical microscope and is attributed to the IrQB aggregates, whose life‐time indicates it is phosphorescent in nature. This aggregate formation is strongly affected by the applied concentrations of IrQB and PMMA in the preparative solution state. Model to postulate the mechanism of aggregate formation in the solution and the derived film states is thereby presented in this study. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 631–639, 2008     

Trifluoromethyl and mixed hydrido trifluoromethyl complexes of iridium(III) as potential precursors of an iridium(I) trifluoromethyl complex

Abstraction of iodide from Ir(CF₃)ClI(CO)(PPh₃)₂ (1) by AgSbF₆ in the presence of acetonitrile yields the cationic complex [Ir(CF₃)Cl(MeCN)(CO)(PPh₃)₂]⁺ [SbF₆]⁻ (2). The acetonitrile group of 2 is readily displaced, and 2 reacts with para-tolyl isocyanide to yield [Ir(CF₃)Cl(CN-p-tolyl)(CO)(PPh₃)₂]⁺ [SbF₆]⁻ (3). The addition of NaOMe to 3 results in the methoxyester complex Ir(CF₃)(COOMe)Cl(CN-p-tolyl) (PPh₃)₂ (4). The acetonitrile ligand of 2 is also displaced by anions, including H⁻. Thus, 2 reacts with LiEt₃BH to give Ir(CF₃)HCl(CO)(PPh₃)₂ (5), in which the hydrido and trifluoromethyl ligands are mutually trans. In contrast, the addition of excess NaBH₄ to 2 affords the novel dihydrido complex trans-Ir(CF3)H₂(CO)(PPh₃)₂ (6). Investigations into the potential use of 5 and 6 as precursors of an iridium(I) complex such as Ir(CF₃)(CO)(PPh₃)₂ are also described.     

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.     

Silica nanoparticles doped with an iridium(III) complex for rapid and fluorometric detection of cyanide

We describe a nanosensor for sensitive and selective detection of cyanide anions. The Ir(III) chlorine bridge complex [Ir(C^N)₂-m-Cl]₂ (Irpq, where pq is C^N = 2-phenyl quinoline) was doped into silica nanoparticles (SiNPs) with a typical size of about 30 nm. The intensity of the yellow emission of the doped SiNPs (under 410 nm exCitation) was strongly enhanced on addition of cyanide ions due to the replacement of chloride by cyanide. The method can detect cyanide ions in the 12.5 to 113 μM concentration range, and the limit of detection is 1.66 μM (at an S/N ratio of 3). The method is simple, sensitive and fast, and this makes it a candidate probe for the fast optical determination of cyanide.

The nanosensor is exploiting the cyanide-induced enhancement of the fluorescence of silica nanoparticles doped with an Ir(III) complex which is the result of the replacement of chloride by cyanide.

     

Electroabsorption study of metal-to-ligand charge transfer in an organic complex of iridium (III)

The dipole moment and polarizability changes have been determined from electroabsorption (EA) spectroscopy of solid films of fac tris(2-(phenyl)pyridinato,N,C^2′)iridium (III) [Ir(ppy)₃]. The maximum changes in the dipole moment |Δμ|_S=(5.0±0.5) D/f (f is the local field correction factor: 1.3–1.7) accompany ground state to the lowest singlet, and |Δμ|_T=(1.7±0.5) D/f ground state to the lowest triplet metal-to-ligand charge transfer (MLCT) excited states formation, while the average polarizability change ų/f² follows from the fitting procedure throughout the visible absorption spectrum range. The experimental values of |Δμ| as well as energy positions of the MLCT states correlate with the literature results of time-dependent density functional theory.