Blue-Emitting Dinuclear N-heterocyclic Dicarbene Gold(I) Complex Featuring a Nearly Unit Quantum Yield

Dinuclear N-heterocyclic dicarbene gold­(I) complexes of general formula [Au₂(RIm-Y-ImR)₂]­(PF₆)₂ (R = Me, Cy; Y = (CH₂)_1–4, <i>o</i>-xylylene, <i>m</i>-xylylene) have been synthesized and screened for their luminescence properties. All the complexes are weakly emissive in solution whereas in the solid state some of them show significant luminescence intensities. In particular, crystals or powders of the complex with R = Me, Y = (CH₂)₃ exhibit an intense blue emission (λ_max = 450 nm) with a high quantum yield (Φ_em = 0.96). The X-ray crystal structure of this complex is characterized by a rather short intramolecular Au···Au distance (3.272 Ǻ). Time dependent density functional theory (TDDFT) calculations have been used to calculate the UV/vis properties of the ground state as well as of the first excited state of the complex, the latter featuring a significantly shorter Au···Au distance

Influence of Halogen Atoms on a Homologous Series of Bis-Cyclometalated Iridium(III) Complexes

A series of homologous bis-cyclometalated iridium­(III) complexes Ir­(2,4-di-X-phenyl-pyridine)₂(picolinate) (X = H, F, Cl, Br) <b>HIrPic</b>, <b>FIrPic</b>, <b>ClIrPic</b>, and <b>BrIrPic</b> has been synthesized and characterized by NMR, X-ray crystallography, UV–vis absorption and emission spectroscopy, and electrochemical methods. The addition of halogen substituents results in the emission being localized on the main cyclometalated ligand. In addition, halogen substitution induces a blue shift of the emission maxima, especially in the case of the fluoro-based analogue but less pronounced for chlorine and bromine substituents. Supported by ground and excited state theoretical calculations, we rationalized this effect in a simple manner by taking into account the σp and σm Hammett constants on both the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) energy levels. Furthermore, in comparison with <b>FIrPic</b> and <b>ClIrPic</b>, the impact of the large bromine atom remarkably decreases the photoluminescence quantum yield of <b>BrIrPic</b> and switches the corresponding lifetime from mono to biexponential decay. We performed theoretical calculations based on linear-response time-dependent density functional theory (LR-TDDFT) including spin–orbit coupling (SOC), and unrestricted DFT (U-DFT) to obtain information about the absorption and emission processes and to gain insight into the reasons behind this remarkable change in photophysical properties along the homologous series of complexes. According to theoretical geometries for the lowest triplet state, the large halogen substituents contribute to sizable distortions of specific phenylpyridine ligands for <b>ClIrPic</b> and <b>BrIrPic</b>, which are likely to play a role in the emissive and nonradiative properties when coupled with the heavy-atom effect

Influence of Halogen Atoms on a Homologous Series of Bis-Cyclometalated Iridium(III) Complexes

A series of homologous bis-cyclometalated iridium­(III) complexes Ir­(2,4-di-X-phenyl-pyridine)₂(picolinate) (X = H, F, Cl, Br) <b>HIrPic</b>, <b>FIrPic</b>, <b>ClIrPic</b>, and <b>BrIrPic</b> has been synthesized and characterized by NMR, X-ray crystallography, UV–vis absorption and emission spectroscopy, and electrochemical methods. The addition of halogen substituents results in the emission being localized on the main cyclometalated ligand. In addition, halogen substitution induces a blue shift of the emission maxima, especially in the case of the fluoro-based analogue but less pronounced for chlorine and bromine substituents. Supported by ground and excited state theoretical calculations, we rationalized this effect in a simple manner by taking into account the σp and σm Hammett constants on both the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) energy levels. Furthermore, in comparison with <b>FIrPic</b> and <b>ClIrPic</b>, the impact of the large bromine atom remarkably decreases the photoluminescence quantum yield of <b>BrIrPic</b> and switches the corresponding lifetime from mono to biexponential decay. We performed theoretical calculations based on linear-response time-dependent density functional theory (LR-TDDFT) including spin–orbit coupling (SOC), and unrestricted DFT (U-DFT) to obtain information about the absorption and emission processes and to gain insight into the reasons behind this remarkable change in photophysical properties along the homologous series of complexes. According to theoretical geometries for the lowest triplet state, the large halogen substituents contribute to sizable distortions of specific phenylpyridine ligands for <b>ClIrPic</b> and <b>BrIrPic</b>, which are likely to play a role in the emissive and nonradiative properties when coupled with the heavy-atom effect

Influence of Halogen Atoms on a Homologous Series of Bis-Cyclometalated Iridium(III) Complexes

A series of homologous bis-cyclometalated iridium­(III) complexes Ir­(2,4-di-X-phenyl-pyridine)₂(picolinate) (X = H, F, Cl, Br) <b>HIrPic</b>, <b>FIrPic</b>, <b>ClIrPic</b>, and <b>BrIrPic</b> has been synthesized and characterized by NMR, X-ray crystallography, UV–vis absorption and emission spectroscopy, and electrochemical methods. The addition of halogen substituents results in the emission being localized on the main cyclometalated ligand. In addition, halogen substitution induces a blue shift of the emission maxima, especially in the case of the fluoro-based analogue but less pronounced for chlorine and bromine substituents. Supported by ground and excited state theoretical calculations, we rationalized this effect in a simple manner by taking into account the σp and σm Hammett constants on both the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) energy levels. Furthermore, in comparison with <b>FIrPic</b> and <b>ClIrPic</b>, the impact of the large bromine atom remarkably decreases the photoluminescence quantum yield of <b>BrIrPic</b> and switches the corresponding lifetime from mono to biexponential decay. We performed theoretical calculations based on linear-response time-dependent density functional theory (LR-TDDFT) including spin–orbit coupling (SOC), and unrestricted DFT (U-DFT) to obtain information about the absorption and emission processes and to gain insight into the reasons behind this remarkable change in photophysical properties along the homologous series of complexes. According to theoretical geometries for the lowest triplet state, the large halogen substituents contribute to sizable distortions of specific phenylpyridine ligands for <b>ClIrPic</b> and <b>BrIrPic</b>, which are likely to play a role in the emissive and nonradiative properties when coupled with the heavy-atom effect

Influence of Halogen Atoms on a Homologous Series of Bis-Cyclometalated Iridium(III) Complexes

A series of homologous bis-cyclometalated iridium­(III) complexes Ir­(2,4-di-X-phenyl-pyridine)₂(picolinate) (X = H, F, Cl, Br) <b>HIrPic</b>, <b>FIrPic</b>, <b>ClIrPic</b>, and <b>BrIrPic</b> has been synthesized and characterized by NMR, X-ray crystallography, UV–vis absorption and emission spectroscopy, and electrochemical methods. The addition of halogen substituents results in the emission being localized on the main cyclometalated ligand. In addition, halogen substitution induces a blue shift of the emission maxima, especially in the case of the fluoro-based analogue but less pronounced for chlorine and bromine substituents. Supported by ground and excited state theoretical calculations, we rationalized this effect in a simple manner by taking into account the σp and σm Hammett constants on both the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) energy levels. Furthermore, in comparison with <b>FIrPic</b> and <b>ClIrPic</b>, the impact of the large bromine atom remarkably decreases the photoluminescence quantum yield of <b>BrIrPic</b> and switches the corresponding lifetime from mono to biexponential decay. We performed theoretical calculations based on linear-response time-dependent density functional theory (LR-TDDFT) including spin–orbit coupling (SOC), and unrestricted DFT (U-DFT) to obtain information about the absorption and emission processes and to gain insight into the reasons behind this remarkable change in photophysical properties along the homologous series of complexes. According to theoretical geometries for the lowest triplet state, the large halogen substituents contribute to sizable distortions of specific phenylpyridine ligands for <b>ClIrPic</b> and <b>BrIrPic</b>, which are likely to play a role in the emissive and nonradiative properties when coupled with the heavy-atom effect

Bright Blue Phosphorescence from Cationic Bis-Cyclometalated Iridium(III) Isocyanide Complexes

We report new bis-cyclometalated cationic iridium­(III) complexes [(C^∧N)₂Ir­(CN-<i>tert</i>-Bu)₂]­(CF₃SO₃) that have <i>tert</i>-butyl isocyanides as neutral auxiliary ligands and 2-phenylpyridine or 2-(4′-fluorophenyl)-R-pyridines (where R is 4-methoxy, 4-<i>tert</i>-butyl, or 5-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 <i>tert</i>-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

Bright Blue Phosphorescence from Cationic Bis-Cyclometalated Iridium(III) Isocyanide Complexes

We report new bis-cyclometalated cationic iridium­(III) complexes [(C^∧N)₂Ir­(CN-<i>tert</i>-Bu)₂]­(CF₃SO₃) that have <i>tert</i>-butyl isocyanides as neutral auxiliary ligands and 2-phenylpyridine or 2-(4′-fluorophenyl)-R-pyridines (where R is 4-methoxy, 4-<i>tert</i>-butyl, or 5-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 <i>tert</i>-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

Charged Bis-Cyclometalated Iridium(III) Complexes with Carbene-Based Ancillary Ligands

Charged cyclometalated (C^∧N) iridium­(III) complexes with carbene-based ancillary ligands are a promising family of deep-blue phosphorescent compounds. Their emission properties are controlled primarily by the main C^∧N ligands, in contrast to the classical design of charged complexes where N^∧N ancillary ligands with low-energy π* orbitals, such as 2,2'-bipyridine, are generally used for this purpose. Herein we report two series of charged iridium complexes with various carbene-based ancillary ligands. In the first series the C^∧N ligand is 2-phenylpyridine, whereas in the second one it is 2-(2,4-difluorophenyl)-pyridine. One bis-carbene (:C^∧C:) and four different pyridine–carbene (N^∧C:) chelators are used as bidentate ancillary ligands in each series. Synthesis, X-ray crystal structures, and photophysical and electrochemical properties of the two series of complexes are described. At room temperature, the :C^∧C: complexes show much larger photoluminescence quantum yields (Φ_PL) of ca. 30%, compared to the N^∧C: analogues (around 1%). On the contrary, all of the investigated complexes are bright emitters in the solid state both at room temperature (1% poly­(methyl methacrylate) matrix, Φ_PL 30–60%) and at 77 K. Density functional theory calculations are used to rationalize the differences in the photophysical behavior observed upon change of the ancillary ligands. The N^∧C:-type complexes possess a low-lying triplet metal-centered (³MC) state mainly deactivating the excited state through nonradiative processes; in contrast, no such state is present for the :C^∧C: analogues. This finding is supported by temperature-dependent excited-state lifetime measurements made on representative N^∧C: and :C^∧C: complexes

Charged Bis-Cyclometalated Iridium(III) Complexes with Carbene-Based Ancillary Ligands

Charged cyclometalated (C^∧N) iridium­(III) complexes with carbene-based ancillary ligands are a promising family of deep-blue phosphorescent compounds. Their emission properties are controlled primarily by the main C^∧N ligands, in contrast to the classical design of charged complexes where N^∧N ancillary ligands with low-energy π* orbitals, such as 2,2'-bipyridine, are generally used for this purpose. Herein we report two series of charged iridium complexes with various carbene-based ancillary ligands. In the first series the C^∧N ligand is 2-phenylpyridine, whereas in the second one it is 2-(2,4-difluorophenyl)-pyridine. One bis-carbene (:C^∧C:) and four different pyridine–carbene (N^∧C:) chelators are used as bidentate ancillary ligands in each series. Synthesis, X-ray crystal structures, and photophysical and electrochemical properties of the two series of complexes are described. At room temperature, the :C^∧C: complexes show much larger photoluminescence quantum yields (Φ_PL) of ca. 30%, compared to the N^∧C: analogues (around 1%). On the contrary, all of the investigated complexes are bright emitters in the solid state both at room temperature (1% poly­(methyl methacrylate) matrix, Φ_PL 30–60%) and at 77 K. Density functional theory calculations are used to rationalize the differences in the photophysical behavior observed upon change of the ancillary ligands. The N^∧C:-type complexes possess a low-lying triplet metal-centered (³MC) state mainly deactivating the excited state through nonradiative processes; in contrast, no such state is present for the :C^∧C: analogues. This finding is supported by temperature-dependent excited-state lifetime measurements made on representative N^∧C: and :C^∧C: complexes

Charged Bis-Cyclometalated Iridium(III) Complexes with Carbene-Based Ancillary Ligands

Charged cyclometalated (C^∧N) iridium­(III) complexes with carbene-based ancillary ligands are a promising family of deep-blue phosphorescent compounds. Their emission properties are controlled primarily by the main C^∧N ligands, in contrast to the classical design of charged complexes where N^∧N ancillary ligands with low-energy π* orbitals, such as 2,2'-bipyridine, are generally used for this purpose. Herein we report two series of charged iridium complexes with various carbene-based ancillary ligands. In the first series the C^∧N ligand is 2-phenylpyridine, whereas in the second one it is 2-(2,4-difluorophenyl)-pyridine. One bis-carbene (:C^∧C:) and four different pyridine–carbene (N^∧C:) chelators are used as bidentate ancillary ligands in each series. Synthesis, X-ray crystal structures, and photophysical and electrochemical properties of the two series of complexes are described. At room temperature, the :C^∧C: complexes show much larger photoluminescence quantum yields (Φ_PL) of ca. 30%, compared to the N^∧C: analogues (around 1%). On the contrary, all of the investigated complexes are bright emitters in the solid state both at room temperature (1% poly­(methyl methacrylate) matrix, Φ_PL 30–60%) and at 77 K. Density functional theory calculations are used to rationalize the differences in the photophysical behavior observed upon change of the ancillary ligands. The N^∧C:-type complexes possess a low-lying triplet metal-centered (³MC) state mainly deactivating the excited state through nonradiative processes; in contrast, no such state is present for the :C^∧C: analogues. This finding is supported by temperature-dependent excited-state lifetime measurements made on representative N^∧C: and :C^∧C: complexes