Optoelectronic properties of green and yellow light-emitting electrochemical cells based on cationic iridium complexes

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 1549 cd m−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.

Graphical abstractConfiguration of light-emitting electrochemical cells (LECs) based on the iridium complexes [Ir(ppz)2(Me-phen)]PF6 (left) and [Ir(dfppy)2(Me-phen)]PF6 (right), which give yellow and green emissions respectively.Figure optionsDownload full-size imageDownload as PowerPoint slide