Effect of the trifluoromethyl on the electronic structure and phosphorescence properties of a series of Ir complexes

The electronic structures and photophysical properties of a series of Ir(III) complexes, Ir(C^C)(ppy)2, Ir(C^C)(ppy)(OrtCF3), Ir(C^C)(ppy)(MeCF3) and Ir(C^C)(ppy)(ParCF3), where ppy=2-phenylpyridine, C^C=1-(2,4-difluorophenyl)-1H-imidazole, OrtCF3=2-(2-(trifluoromethyl)phenyl)pyridine, MeCF3=2-(3-(trifluoromethyl)phenyl)-pyridine, and ParCF3=2-(4-(trifluoromethyl)phenyl)pyridine, were investigated by density functional theory calculation employing the mPW1PW91 density functional. The simulated electronic structure, absorption spectra, and phosphorescence of Ir(C^C)(ppy)2 were in good agreement with the experimental values. Compared with Ir(C^C)(ppy)2, it was found that introduction of the CF3 substituent on the ortho -and para -position of ppy was more useful to strength the metal-ligand bond, enhance the electron injection ability, as well as red-shifted the absorption spectra and phosphorescence. Furthermore, Ir(C^C)(ppy)(OrtCF3) had increased participation of triplet metal to ligand charge transfer (3MLCT) contributions, large transition dipole moment ( m S1) and d orbital splitting, small singlet-triplet splitting energy (D E S1-T1) compared with other complexes, which indicated Ir(C^C)(ppy)(OrtCF3) would be potential phosphorescence emitters with high quantum yield.