Tuning of Wavelengths:  Synthesis and Photophysical Studies of Iridium Complexes and Their Applications in Organic Light Emitting Devices

Abstract

We have prepared and characterized a series of substituted 2-phenylbenzthiazole (4-CF3, 4-Me, 4-OMe, 4-F, 4-CN, and 3-F) ligands. The intermediate di-irrido and the six-coordinated mononuclear iridium(III) dopants of the above ligands have been synthesized and characterized. These complexes are thermally stable between 275 and 300 °C depending upon the types and volatility of substituents. They emit bright yellow to orange light. The peak emission wavelengths of the dopants can be finely tuned depending upon the electronic properties of the substituents as well as their positions in the ring. In the absorption spectra, the 1MLCT and 3MLCT transitions have been resolved in the range of 385−450 nm. The long tail toward lower energies are assigned to 3MLCT and 3π−π* transitions, which gains intensity by mixing with the higher lying 1MLCT state through the spin−orbit coupling of iridium(III). All complexes exhibit one electron oxidation and the oxidation potential values can be correlated with the Hammett substituent constants. The electroluminescent characteristics for the substituted and the unsubstituted complexes have been compared and discussed.

Synthetically Tailored Excited States: Phosphorescent, Cyclometalated Iridium(III) Complexes and Their Applications

“…[11] As our understanding of structure-property relationships improves, we have found that DFT calculations provide an excellent method for modeling orbital configurations and extrapolating the energy of the lowest excited state. [11,14] These tech-A C H T U N G T R E N N U N G niques in conjunction with the other strategies presented herein have facilitated and expedited the design of useful materials for various optoelectronic, [4,39] analytical, [3,16] and photocatalytic applications. [18] Four areas in which the highly tunable nature of iridiumA C H T U N G T R E N N U N G (III) complexes have improved the performance of inorganic materials are discussed below.…”

“…Electron-withdrawing substituents tend to stabilize the HOMO by removing electron density from the metal, whereas donating groups have an inverse effect. [11,14,39,40] This relationship is convoluted by the fact that withdrawing groups may also lower the energy of the LUMO (i.e., increasing the electron affinity of the parent ligand). [14] Fortunately, the cyclometalating and ancillary ligands can be separately substituted with electron-withdrawing and A C H T U N G T R E N N U N G -donating groups in heteroleptic complexes, which enables deliberate control over the excited state.…”

A Series of Red‐Light‐Emitting Ionic Iridium Complexes: Structures, Excited State Properties, and Application in Electroluminescent Devices

“…[1][2][3][4][5][6] In particular, ionic Ir complexes have emerged as promising chromophoric materials for lighting and display applications according to the reports of recent studies. [7][8][9][10][11][12][13][14][15] Inert metal electrodes that are resistant to oxidation in air can be used in these devices and the power consumptions of these devices are low.…”

“…[9,10] As one of the three primary colors for electrochemical properties. It was found that the excited state of the [Ir(piq) 2 (FbpyF)](PF 6 ) complex can be assigned to a mixed character of 3 LC (π N ∧ N Ǟπ* N ∧ N ), 3 MLCT, 3 LLCT (π C ∧ N Ǟπ* N ∧ N ), and 3 LC (π C ∧ N Ǟπ* C ∧ N ). In addition, the alkylfluorene-substituted complex, [Ir(piq) 2 (FbpyF)](PF 6 ), had relatively high quantum efficiency and good film-forming ability, and it was expected to be a good candidate for lighting and display applications.…”

Highly Efficient Red Phosphorescent OLEDs Based on Ir(III) Complexes with Fluorine-substituted Benzoylphenylpyridine Ligand

“…This indicates that the energy levels differ according to the position of the fluorine. 1,27 Their emission quantum yields were 0.36, 0.26, 0.36 and 0.28, respectively, as determined using Ir(ppy) 3 (0.40) used as the reference. 28 The respective HOMO energy levels of 1-4 were measured at -5.68, -5.86, -5.77 and -5.51 eV by low-energy photoelectron spectrometer (Riken-Keiki AC-2).…”