Blue-to-Green Emitting Neutral Ir(III) Complexes Bearing Pentafluorosulfanyl Groups: A Combined Experimental and Theoretical Study

Abstract

A structure–property relationship study of neutral heteroleptic (1 and 2, [Ir(C∧N)2(L∧X)]) and homoleptic (3 and 4, fac-[Ir(C∧N)3]) Ir(III) complexes (where L∧X = anionic 2,2,6,6-tetramethylheptane-3,5-dionato-κO3,κO6 (thd) and C∧N = a cyclometalating ligand bearing a pentafluorosulfanyl (−SF5) electron-withdrawing group (EWG) at the C4 (HL1) and C3 (HL2) positions of the phenyl moiety) is presented. These complexes have been fully structurally characterized, including by single-crystal X-ray diffraction, and their electrochemical and optical properties have also been extensively studied. While complexes 1 ([Ir(L1)2(thd)]), 3 (Ir(L1)3), and 4 (Ir(L2)3) exhibit irreversible first reduction waves based on the pentafluorosulfanyl substituent in the range of −1.71 to −1.88 V (vs SCE), complex 2 ([Ir(L2)2(thd)]) exhibits a quasi-reversible pyridineC∧N-based first reduction wave that is anodically shifted at −1.38 V. The metal + C∧N ligand oxidation waves are all quasi-reversible in the range of 1.08–1.54 V (vs SCE). The optical gap, determined from the lowest energy absorption maxima, decreases from 4 to 2 to 3 to 1, and this trend is consistent with the Hammett behavior (σm/σp with respect to the metal–carbon bond) of the −SF5 EWG. In degassed acetonitrile, for complexes 2–4, introduction of the −SF5 group produced a blue-shifted emission (λem 484–506 nm) in comparison to reference complexes [Ir(ppy)2(acac)] (R1, where acac = acetylacetonato) (λem 528 nm in MeCN), [Ir(CF3-ppy) (acac)] (R3, where CF3-ppyH = 2-(4-(trifluoromethyl)phenyl)pyridine) (λem 522 nm in DCM), and [Ir(CF3-ppy)3] (R8) (λem 507 nm in MeCN). The emission of complex 1, in contrast, was modestly red shifted (λem 534 nm). Complexes 2 and 4, where the −SF5 EWG is substituted para to the Ir–CC∧N bond, are efficient phosphorescent emitters, with high photoluminescence quantum yields (ΦPL = 58–79% in degassed MeCN solution) and microsecond emission lifetimes (τε = 1.35–3.02 μs). Theoretical and experimental observations point toward excited states that are principally ligand centered (3LC) in nature, but with a minor metal-to-ligand charge-transfer (3MLCT) transition component, as a function of the regiochemistry of the pentafluorosulfanyl group. The 3LC character is predominant over the mixed 3CT character for complexes 1, 2, and 4, while in complex 3, there is exclusive 3LC character as demonstrated by unrestricted density functional theory (DFT) calculations. The short emission lifetimes and reasonable ΦPL values in doped thin film (5 wt % in PMMA), particularly for 4, suggest that these neutral complexes would be attractive candidate emitters in organic light-emitting diodes.

High‐Efficiency Deep‐Blue‐Emitting Organic Light‐Emitting Diodes Based on Iridium(III) Carbene Complexes

“…Three issues arise when employing this strategy. The first is that the electrochemical stability of fluoro substituents, the most popular electron‐withdrawing substituent, such as in the widely studied FIrpic [iridium(III)bis(4,6‐difluopyridinato‐N,C 2′ )picolinate] sky blue emitter, is poor, translating to greatly reduced device stability; while the use of other more strongly electron‐withdrawing substituents do not necessarily translate into bluer‐emitting complexes, despite deepening the highest occupied molecular orbital (HOMO) of the compound . The second is that as the energy of the emissive triplet state increases, nonradiative recombination via thermally accessible metal‐centered excited states becomes increasingly problematic, leading to emitter degradation .…”

Amine–borane complex-initiated SF5Cl radical addition on alkenes and alkynes

“…Considering the wide range of trifluoromethylated compounds of interest, the synthesis of their SF 5 -analogs has become a trend to increase the properties of these valuable molecules [ 9 ]. Due to the unique properties, the SF 5 group has been used in various fields of chemistry, including pharmaceuticals [ 10 – 16 ], agrochemistry [ 17 – 20 ], and materials sciences [ 21 – 26 ]. The applications have, however, been limited by the poor synthetic accessibility of SF 5 -containing molecules.…”

Tackling the Self‐Aggregation of IrIII Complexes: A Theoretical Study

“…For the D1 R series, it was observed that in general the introduction of the substituents induced a small hypsochromic shift on their absorption spectra (Figure b). This effect is due to a greater HOMO stabilization when compared to the LUMO stabilization . Particularly, D1h in the external chemical environment has exhibited the largest HOMO–LUMO gap of about 4.79 eV ( λ max = 276 nm, Figures S11 and S12).…”