Insight into understanding the photo-chemical stability of bis-tridentate Ir(III) phosphors: A theoretical perspective

Abstract

Recently, Chen et al. reported an experimental result of photo-stability of a series of bis-tridentate Ir(III) phosphors (m2h-2 and m6h) that the photo-stability of the Ir(III) phosphors strongly depends of bond strength between carbon in pyrimidine and pyrazole or phenyl fragment. In this report, the photo-, and electro-chemical stability at excited states of bis-tridentate Ir(III) phosphors were theoretically investigated by employing density functional theory (DFT) simulation. It was revealed that the most favorable geometry of triplet metal-centered (3MC) state in bis-tridentate Ir(III) phosphors were originated from a ligand rupture of Ir–N bond at pyrimidine unit, where the calculated ΔE(3MC-T1) values of m2h-2 and m6h-2 phosphors were 0.06 eV and 0.23 eV, respectively and surprisingly, the rate constant of photo degradation of m2h-2, m6h-2, and Ir(ppy)3 is linearly proportional to the ΔE(3MC-T1) values. This result suggests that large ΔE(3MC-T1) is the detrimental factor for chemical stability of high-energy Ir(III) phosphors.