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Green- and yellow-emitting cationic iridium complexes, [Ir(dfppy) 2 (pybi)]PF 6 (Complex 1) and [Ir(ppz) 2 (pybi)]PF 6 (Complex 2), were synthesized using 2-(2,4-difluorophenyl)pyridine (Hdfppy) and 1-phenylpyrazole (Hppz) as the cyclometalating ligands and 2-(2-pyridyl)benzimidazole (pybi) as the ancillary ligand. In order to gain insight into the photophysical and electrochemical behavior, density functional theory (DFT) calculations were simulated on the above complexes, which showed consistency in energy gaps obtained from both experimental and theoretical results. Light-emitting electrochemical cells (LECs) based on Complex 1 were obtained by solution-processed fabrication, and they showed green (523 nm) electroluminescence with Commission Internationale de L'Eclairage (CIE) coordinates of (0.33, 0.58); on the other hand, the LEC utilizing Complex 2 showed yellow electroluminescence with CIE coordinates of (0.41, 0.56). The highest luminance of 1492 cd m −2 and current density of 83.13 mA cm −2 were achieved for the LEC utilizing Complex 2, owing to the more balanced carrier injection and recombination as compared to those for Complex 1. The negative role of the free – NH group in the electroluminescent properties of LECs is confirmed by comparing the current results with those previously reported for N-alkylated benzimidazole moieties. [ABSTRACT FROM AUTHOR]

Highlights: [•] Cationic iridium complexes were synthesized using imidazole based ancillary ligand. [•] Light-emitting electrochemical cells (LECs) were fabricated and characterized. [•] LECs based on these complexes resulted in green and blue–green light emission. [•] Imidazole based ancillary ligands are good candidate to destabilize LUMO orbitals. [ABSTRACT FROM AUTHOR]

Abstract: Green and yellow light emitting phosphorescent iridium complexes with 5-methyl-1,10-phenanthroline as an ancillary ligand were synthesized and characterized for the fabrication of light-emitting electrochemical cells (LECs). The photophysical and electrochemical properties of the resulting complexes, [Ir(dfppy)2(Me-phen)]PF6 (1) and [Ir(ppz)2(Me-phen)]PF6 (2) (where dfppy=2-(2,4-difluorophenyl)pyridine; ppz=1-phenylpyrazole, Me-phen=5-methyl-1,10-phenanthroline) were investigated by means of UV–Vis absorption, fluorescence spectroscopy and cyclic voltammetry. Density functional theory (DFT) calculations were performed to gain insight into the photophysical and electrochemical behaviors and to determine the electronic energy levels for the complexes. LECs were fabricated based on these complexes and their electroluminescent properties were investigated, which resulted in a maximum luminance of 2430 and 1549cdm−2 for complexes 1 and 2 respectively. LECs incorporating these heteroleptic complexes effectively tuned the emission color through the meticulous selection of the cyclometallated ligands and they displayed highly luminescent green and yellow electroluminescence with the Commission Internationale de L’Eclairage (CIE) coordinates of (0.25, 0.58) and (0.42, 0.54) for complexes 1 and 2 respectively. [Copyright &y& Elsevier]

Abstract: Highly luminescent light-emitting electrochemical cells (LECs) based on cationic iridium complexes [Ir(ppz)2(dpphen)]PF6 (1) and [Ir(ppz)2(tmphen)]PF6 (2) (ppz is 1-phenylpyrazole, dpphen is 4,7-diphenyl-1,10-phenanthroline and tmphen is 3,4,7,8-tetramethyl-1,10-phenanthroline) with phenanthroline based ancillary ligands were fabricated using air stable electrodes and their electroluminescent properties were investigated. LECs based on complex 1 emitted yellow electroluminescence (λ max 574nm) with Commission Internationale de L’Eclairage (CIE) coordinates of (0.49, 0.50) while the complex 2 gave yellowish-green electroluminescence (λ max 537nm) with CIE coordinates of (0.35, 0.58). The work done here reveals that the alkyl substituted phenanthroline ancillary ligand, tmphen shifts the light emission to the shorter wavelength region than the phenyl substituted dpphen ligand, resulting in the color tuning of the light-emitting devices. Density functional theory (DFT) calculations were performed to gain insight into the molecular surfaces of cationic iridium complexes and their electrochemical behaviors. Single layer LECs based on these complexes exhibited a high luminescence of 5199 and 4751cd/m2 for complexes 1 and 2 respectively. The ionic liquid, 1-ethyl-3-methylimidazolium hexafluorophosphate (EMIMPF6) was added to the light emitting layer and hence higher luminances were obtained than the pristine device. [Copyright &y& Elsevier]