Synthesis, Photophysical and Electrochemical Characterization of the Heteroleptic Iridium Complexes with Modified Ancillary Ligand by Carrier-transporting Groups

Two heteroleptic iridium complexes with a general formulation of (piq)(2)Ir(G-pic) were synthesized and characterized by H-1 NMR, C-13 NMR and element analysis, in which piq is 1-phenylisoquinoline, G-pic is picolinic acid derivative containing carrier-transporting group by a non-conjugated connection of 1,6-dioxyhexane. Both (piq)(2)Ir(G-pic) complexes exhibited an enhanced UV absorption band at 310-400 nm, an increased HOMO energy level and an identical red emission peaked at 612 nm with higher fluorescence quantum efficiency (Phi(f)), compared to (piq)(2)Ir(pic) in dichloromethane solution. Interestingly, this iridium complex containing both hole-transporting triphenylamine and electron-transporting oxadiazole moieties exhibited the best Phi(f) of 0.58 using Ru(bpy)(3)(PF6)(2) as the reference (Phi(f)=0.062 in acetonitrile). This work indicates that incorporating carrier-transporting groups into ancillary ligand by a non-conjugated connection is available for improving the optophysical properties of their iridium complexes.