Theoretical study on the influence of ancillary and cyclometalated ligands on the electronic structures and optoelectronic properties of heteroleptic iridium(iii) complexes

Abstract

We report a theoretical analysis of a series of heteroleptic iridium(III) complexes (dox)₂Ir(acac) [dox = 2,5-diphenyl-1,3,4-oxadiazolato-N,C², acac = acetylacetonate] (1a), (fox)₂Ir(acac) [fox = 2,5-bis(4-fluorophenyl)-1,3,4-oxadiazolato-N,C²] (1b), (fox)₂Ir(Et₂dtc) [Et₂dtc = N,N′-diethyldithiocarbamate] (2), (fox)₂Ir(Et₂dtp) [Et₂dtp = O,O′-diethyldithiophosphate] (3), (pypz)₂Ir(acac) [pypz = 3,5-di(2-pyridyl)pyrazole] (4a), (O-pypz)₂Ir(acac) (4b), (S-pypz)₂Ir(acac) (4c) and (bptz)₂Ir(acac) [bptz = 3-tert-butyl-5-(2-pyridyl)triazole] (5) by using the density functional theory (DFT) method to investigate their electronic structures and photophysical properties and obtain further insights into the phosphorescent efficiency mechanism. Meanwhile, we also investigate the influence of ancillary and cyclometalated ligands on the properties of the above complexes. The results reveal that the nature of the ancillary ligands can influence the electron density distributions of frontier molecular orbitals and their energies, resulting in change in transition character and emission color, while the different cyclometalated ligands have a large impact on the charge transfer performances of the studied complexes. The calculated absorption and luminescence properties of the four complexes 1a, 1b, 2 and 3 are compared with the available experimental data and a good agreement is obtained. Further, the assumed complexes 4a and 4b possess better charge transfer abilities and more balanced charge transfer rates, and they are potential candidates as blue-emitting materials.