Neutral 2-phenylbenzimidazole-based iridium(III) complexes with picolinate ancillary ligand: tuning the emission properties by manipulating the substituent on the benzimidazole ring

We report the synthesis and characterization of ten neutral bisheteroleptic iridium(III) complexes with 2-phenylbenzimidazole cyclometallating ligand and picolinate as ancillary ligand. The 2-phenylbenzimidazole has been modified by selected substituents introduced on the cyclometallating ring and/or on the benzimidazole moiety. The integrity of the complexes has been assessed by NMR spectroscopy, by high-resolution mass spectrometry and by elemental analysis. The complexes are demonstrated to be highly phosphorescent at room temperature and a luminescence study with comprehensive ab initio calculations allow us to determine the lowest emitting excited state which depends on the substituent nature and its position on the cyclometallating ligand.

Bis-Heteroleptic Cationic Iridium(III) Complexes Featuring Cyclometalating 2-Phenylbenzimidazole Ligands: A Combined Experimental and Theoretical Study

In this report, we investigate a new family of cationic iridium(III) complexes featuring the cyclometalating ligand 2-phenylbenzimidazole and ancillary ligand 4,4'-dimethyl-2,2'-bipyridine. Our benchmark complex IrL¹₂ (L¹ = 2-phenylbenzimidazole) displays emission properties similar to those of the archetypical complex 2,2'-dipyridylbis(2',4'-phenylpyridine)iridium(III) in deaerated CH₃CN (Φ = 0.20, λ_em = 584 nm and Φ = 0.14, λ_em = 585 nm, respectively) but exhibits a higher photoluminescence quantum yield in deaerated CH₂Cl₂ (Φ = 0.32, λ_em = 566 nm and Φ = 0.20, λ_em = 595 nm, respectively) and especially a lower nonradiative constant (k_nr = 6.6 × 10⁵ s^-1 vs k_nr = 1.4 × 10⁶ s^-1, respectively). As a primary investigation, we explored the influence of the introduction of electron-donating and electron-withdrawing groups on the benzimidazole moiety and the synergetic effect of the substitution of the cyclometalating phenyl moiety at the para position with the same substituents. The emission energy displays very good correlation with the Hammett constants of the introduced substituents as well as with ΔE_redox values, which allow us to ascribe the phosphorescence of these series to emanate mainly from a mixed metal/ligand to ligand charge transfer triplet excited state (³M/LLCT*). Two complexes (IrL⁵₂ and IrL⁸₂) display a switch of the lowest triplet excited state from ³M/LLCT* to ligand centered (³LC*), from the less polar CH₂Cl₂ to the more polar CH₃CN. The observed results are supported by (TD)-DFT computations considering the vibrational contributions to the electronic transitions. Chromaticity diagrams based on the maximum emission wavelength of the recorded and simulated phosphorescence spectra demonstrate the strong promise of our complexes as emitting materials, together with the very good agreement between experimental and theoretical results.

Study of a phosphorescent cationic iridium(III) complex displaying a blue-shift in crystals

We report the synthesis and the characterization of a new cationic iridium(III) complex featuring two 1-(p-methoxyphenyl)-5-methoxybenzimidazole cyclometallating ligands and a dimethylbipyridine ancillary ligand. The complex has been fully characterized by 1D and 2D NMR (¹H, ¹³C, ¹⁹F and ³¹P), elemental analysis and high-resolution mass spectrometry (HRMS). The photoluminescence studies performed in a solution, on amorphous powder and on crystals revealed an unexpected behavior. Indeed, the emission spectra observed in both solution (CH₂Cl₂) and amorphous powder samples are centered at around 580 nm, whereas in crystals the emission displays a large hypsochromic shift of ∼800 cm^-1 (λ_em = 558 nm). X-ray diffraction experiments, photophysical studies and DFT calculations allow for rationalizing the hypsochromic shift.

Experimental Electrochemical Potentials of Nickel Complexes

Nickel-catalyzed cross-coupling and photoredox catalytic reactions has found widespread utilities in organic synthesis. Redox processes are key intermediate steps in many catalytic cycles. As a result, it is pertinent to measure and document the redox potentials of various nickel species as precatalysts, catalysts, and intermediates. The redox potentials of a transition-metal complex are governed by its oxidation state, ligand, and the solvent environment. This article tabulates experimentally measured redox potentials of nickel complexes supported on common ligands under various conditions. This review article serves as a versatile tool to help synthetic organic and organometallic chemists evaluate the feasibility and kinetics of redox events occurring at the nickel center, when designing catalytic reactions and preparing nickel complexes.

1 Introduction

1.1 Scope

1.2 Measurement of Formal Redox Potentials

1.3 Redox Potentials in Nonaqueous Solution

2 Redox Potentials of Nickel Complexes

2.1 Redox Potentials of (Phosphine)Ni Complexes

2.2 Redox Potentials of (Nitrogen)Ni Complexes

2.3 Redox Potentials of (NHC)Ni Complexes

Synthesis and luminescence properties of two Ir(iii) complexes containing styrene-modified phenylpyridine ligands

Two green-emitting iridium(iii) complexes containing styrene-modified phenylpyridine ligands have been synthesized for OLEDs.

ZnO-NP assisted synthesis of fluorescent β-carboline C-1 tethered benzimidazole/benzothiazole/benzoxazole derivatives and assessment of their photophysical properties

A facile transformation of 1-formyl β-carboline into fluorescent β-carboline C-1 tethered benzazole derivatives is described under the catalysis of ZnO nanoparticles.

Highly efficient bluish green organic light-emitting diodes of iridium(iii) complexes with low efficiency roll-off

Two novel iridium(iii) complexes Ir(BTBP)2mepzpy and Ir(BTBP)2phpzpy were successfully synthesized, in which 2',6'-bis(trifluoromethyl)-2,4'-bipyridine (BTBP) was used as the main ligand, and 2-(3-methyl-1H-pyrazol-5-yl)pyridine (mepzpy) and 2-(3-2-(3-phenyl-1H-pyrazol-5-yl))pyridine (phpzpy) were introduced as the ancillary ligands, respectively. Both Ir(iii) complexes displayed bluish green emission peaks at 486 and 487 nm with high quantum efficiencies of 0.73 and 0.69, respectively. The organic light-emitting diodes (OLEDs) with the structure of ITO/HATCN (hexaazatriphenylenehexacarbonitrile, 5 nm)/TAPC (bis[4-(N,N-ditolylamino)-phenyl]cyclohexane, 40 nm)/Ir(BTBP)2mepzpy or Ir(BTBP)2phpzpy (10 wt%): 2,6-DCzPPy (2,6-bis(3-(9H-carbazol-9-yl)phenyl)pyridine, 10 nm)/TmPyPB (1,3,5-tri[(3-pyridyl)-phen-3-yl]benzene, 30 nm)/LiF (1 nm)/Al (100 nm) exhibited high efficiencies with low efficiency roll-off. Especially, the device based on the Ir(BTBP)2mepzpy complex achieved a maximum current efficiency of 58.17 cd A-1 and a maximum external quantum efficiency of 25.33% with Commission Internationale de 1'Eclairage coordinates of (0.19, 0.43). These results indicate that novel cyclometalated Ir(iii) complexes for high efficiency OLEDs with low efficiency roll-off were obtained by our rational design.

Efficient green phosphorescent Ir(iii) complexes with β-diketonate ancillary ligands

Three new iridium complexes with β-diketonate ancillary ligands were synthesized as emissive materials for organic light-emitting devices.

Synthesis and properties of wide bandgap polymers based on tetraphenylsilane and their applications as hosts in electrophosphorescent devices

By introducing the electron-withdrawing diphenylphosphine oxide in PFSCPO, its doped OLEDs achieve enhanced current and external quantum efficiencies than the PFSC-hosted device.

New amide based iridium(iii) complexes: synthesis, characterization, photoluminescence and DFT/TD-DFT studies

The photophysical properties of new iridium complexes have been investigated depending on various solvents and substituents and DFT/TD-DFT studies have supported observed optical data.