Luminescence Comparison of Iridium(III) Complexes Containing Symmetric vs. Asymmetric Quinolinate Ligands

Abstract

We have focused our research on development of the iridium complexes, especially with respect to blue and red emission for OLED. Previously, we prepared bis-[2,3-bis(4-fluorophenyl)quinoxalinato]iridium(acetylacetonate) [Ir(2,3-dpqx-F2)2(acac)] where the main ligand, 2,3-dpqx-F2, itself is symmetric. The luminescence spectra of Ir(2,3-dpqx-F2)2(acac) revealed red emission with the peak at approximately 640 nm with the CIE coordinates of (0.684, 0.311). Recently, Johannes et al. reported the iridium complexes containing fluorophenylmethylquinoxaline derivatives (fpmqx) as asymmetric main ligands and investigated their luminescence properties. Herein, we synthesized symmetric Ir(2,3-dpqx-F2)2(AL) and asymmetric Ir(fpmqx)2(AL) and compared their emission patterns and characteristics where accetylacetonate (acac) and 2-(5-(trifluoromethyl)-2H-1,2,4-triazol-3-yl)pyridine (trzl-CH3) were introduced as ancillary ligands(AL). We investigated the emission properties of Ir(2,3-dpqx-F2)2(AL) and Ir(fpmqx)2(AL), and found that asymmetric Ir(fpmqx)2(AL) showed blue-shifted photoluminescence compared with symmetric Ir(2,3-dpqx-F2)2(AL). We also estimated the energy gap between the HOMO and LUMO of the complexes with electrochemical properties measured by cyclic voltammetry.