Theoretical investigation of the effects of N-substitution on the photophysical properties of two series of iridium(iii) complexes

Based on the complexes [Ir(dfb-pz)₂(tfmtyp)] (1) and [Ir(tfmfb-pz)₂(tfmtyp)] (2) [dfb-pz = 2,4-difluorobenzyl-N-pyrazole; tfmtyp = 2-(5-trifluoromethyl-[1,2,4]triazol-3-yl)-pyridine; tfmfb-pz = 2-tri-fluoromethyl-5-fluorobenzyl-N-pyrazole], two series of Ir(iii) complexes have been designed by substituting "CH" groups with the N atom at -a, -b, -c, and -d positions on the pyridine moiety in N^N ligands. The electronic structure, absorption and emission spectra as well as phosphorescence efficiency of all these Ir(iii) complexes were investigated by using density functional theory (DFT) and time-dependent DFT (TDDFT) methods. The calculated results show that the assumed complexes 1a and 2a may possess a higher photoluminescent quantum efficiency than other complexes and are potential candidates as efficient blue-emitting materials. This study shows that the N substitution can tune the emission color of 1 and 2 and enhance the photoluminescence quantum efficiency.