The insights from theoretical calculation on the photophysical properties of a series of phosphorescent iridium(III) complexes

The electronic structure and photophysical properties of three Ir(III) complexes with the substituted 5,5'-di(trifluoromethyl)-3,3'-bipyrazole(bipz) ligand have been theoretically investigated by using density functional theory and time-dependent density functional theory method. The calculated results show that the energy gaps between of LUMO and HOMO (Delta E-L -> H) of complexes 1, 2 and 3 are gradually decreased, that is, 3.54 eV, 3.07 eV and 2.95 eV for 1, 2 and 3, respectively. The lowest energy absorption wavelength of 1, 2 and 3 are located at 443 nm, 532 nm and 564 nm, respectively. The calculated 443 nm absorption for 1 is in good agreement with the experimental value. The lowest energy emissions of complexes 1, 2 and 3 are localized at 545 nm, 679 nm and 731 nm, respectively, simulated in CH2Cl2 medium at TPSSH level. The conclusion can be drawn that the different substituent groups in the bipz ligand results in the important effect on the electronic structure and photophysical properties. The research work can provide valuable information for the design of new organic light-emitting diodes materials.