Theoretical investigation of the vibronic phosphorescence spectra and quantum yields for iridium(III) complexes with 2-(2,5,2′,3′,4′,5′,6′-heptafluoro-biphenyl-4-yl)-pyridine as the primary ligand

Cyclometalated Ir(III) complexes are widely used as phosphorescent materials in organic light-emitting diodes. In this work, the vibrationally resolved phosphorescence spectra of an experimental reported and four novel designed Ir(III) complexes with 2-(2,5,2',3',4',5',6'-heptafluoro-biphenyl-4-yl)-pyridine (HFYP) as primary ligand are investigated by theoretical calculations. The ancillary ligands are 3-(pentafluorophenyl)-pyridin-2-yl-1,2,4-triazolate (exp3), 3-(trifluoromethyl)-pyridin-2-yl-1,2,4-triazolate (5), 5-methylsulfonyl-2-oxyphenyl-2-oxazole (6), 5-trifluoromethyl-2-oxyphenyl-2-oxazole (7), 2-(3-(trifluoromethyl)-1H-1,2-diazol-5-yl)pyridine (8), respectively. Phosphorescence spectra show that there are mainly two strong peaks, which can be ascribed as low-frequency vibrational modes such as the rotation of ligand plane, and benzene ring/pyridine ring in ligand HFYP1 skeleton vibration coupled with C-H in pyridine ring in plane bending vibration. The phosphorescence quantum yields were quantitatively determined by evaluating radiative decay rate constant k(r), intersystem crossing rate constatant k(ISC) and temperature-dependent nonradiative decay rate constant k(nr)(T). It shows that the quantum yields of compounds exp3, 5 and 8 are relative higher, while those of compounds 6 and 7 are much smaller. This is mainly caused by larger k(nr)(T) of compounds 6 and 7. It is anticipated that in Ir(III) complex with HFYP primary ligand, pyridin-2-yl-1,2,4-triazolate, 1,2-diazol-5-yl-pyridine are good ancillary ligand, while 2'-oxyphenyl-2-oxazoline is not appropriate to be ancillary ligand. (C) 2019 Published by Elsevier B.V.