The effects of substituted picolinate ligands on the photophysical and electrochemiluminescence properties of bis-cylcometalated iridium(III) complexes

Abstract

The bicyclometalated iridium(III) complexes bearing 2,4-diphenylquinoline with fluorinated picolinates and methoxy picolinates as ancillary ligands were synthesized, and the effects of substituent groups at the ancillary ligands on the photophysical and electrochemiluminescent properties of the cyclometalated iridium(III) complexes were also investigated. The cyclometalated iridium(III) complexes with methoxy picolinates were obtained by a tandem reaction under a mild condition. All these complexes display the intense orange phosphorescence with the peak wavelengths at 586–600 nm. It is significant to note that the 6-position substitution of picolinates reduces the stability of the cyclometalated iridium(III) complexes, and the luminous and electrochemiluminescence (ECL) efficiency is accordingly reduced. Electrochemical testing suggested that the low oxidation potential could be beneficial to improve ECL efficiency. Moreover, the electron-donating methoxy group may result in the increase of photoluminescence (PL) and ECL efficiencies of the iridium(III) complexes, whereas the electron-withdrawing fluorine groups may lead to reducing of both PL and ECL efficiencies. Especially, the ECL intensity of the cyclometalated iridium(III) complex with 3,5-dimethoxy picolinate is ca. 11 times higher than that of the typical [Ru(bpy)3]2+(bpy = 2,2′-bipyridine).The ECL intensity of complex MeOIr4 is 11 times higher than that of the typical [Ru(bpy)3]2+.