Rational Tuning of Bis-Tridentate Ir(III) Phosphors to Deep-Blue with High Efficiency and Sub-microsecond Lifetime

Abstract

A new class of bis-tridentate Ir(III) complexes (Dap-1−4) was synthesized using carbene pincer pro-chelates PC1•H 3 (PF 6 ) 2 or PC2•H 3 (PF 6 ) 2 with either imidazolylidene or imidazo [4,5-b]pyridin-2-ylidene appendages, together with a second cyclometalating 2,6-diaryoxypyridine chelate, L1H 2 and L2H 2 , differed by a NMe 2 donor at the central pyridinyl fragment. The respective emission tuning between the ultraviolet and blue region was rationalized using time-dependent density functional theory (TD-DFT) approaches. Next, a highly efficient blue emitter (Dap-5) was synthesized by concomitant addition of two methyl groups and a single CF 3 substituent at the central phenyl and peripheral imidazo[4,5-b]pyridin-2-ylidene entities of the carbene pincer chelate, respectively. The organic light-emitting diode (OLED) device with 15 wt % Dap-5 in DPEPO shows electroluminescence at 468 nm and with CIE (0.14, 0.15) and a max external quantum efficiency (max EQE) of 16.8% with low efficiency roll-off (EQE of 14.4% at 1000 cd m −2 ); the latter is attributed to the relatively shortened triplet excitedstate radiative lifetime. These results highlight the adequateness of bis-tridentate Ir(III) phosphors in fabrication of practical blue-emitting OLEDs.

Probing Electron Excitation Characters of Carboline-Based Bis-Tridentate Ir(III) Complexes

“…In summary, by introducing varied substituents at the 4-position of central pyridinyl fragment of dianionic chelate or on the central phenyl coordination unit of carboline-based monoanionic pincer chelate, a series of five bis-tridentate Ir(III) complexes were successfully designed and synthesized, with an isolation yield higher than 50% and absence of any isomeric product. This result is consistent with those documented in literature [ 37 , 43 ]. The addition of methoxy and dimethylamino substituents at the 4-position of central pyridinyl fragment of dianionic chelate effectively increased the electron density at the Ir(III) metal center, which increased the MLCT contribution at the excited states, and gave a structureless emission profile.…”

“…The phyz1 chelate is essentially planar, while that of the tridentate chelate cbF underwent a slight distortion at the outer hexagonal ring of the carboline unit, which can be attributed to the unfavourable steric interaction between carboline and central benzene fragments. In agreement with the prediction of trans-influence [ 42 ], the carbene Ir-C distance (Ir-C(39) = 2.004(3) Å) is relatively shorter than the typical Ir-C distances observed in other bis-tridentate Ir(III) complexes bearing symmetrically arranged carbene pincer chelates (2.043 − 2.062 Å) [ 43 , 44 ]. Concomitantly, the Ir-C distance of central benzene group (Ir-C(31) = 2.011(3) Å) elongated slightly in comparison to that of the corresponding carbene pincer chelates (1.950–1.960 Å).…”

Iridium(III) Phosphors–Bearing Functional 9‐Phenyl‐7,9‐dihydro‐8H‐purin‐8‐ylidene Chelates and Blue Hyperphosphorescent OLED Devices

“…[ 15 ] Substitution of chloro group with aniline and 3‐( tert ‐butyl)aniline was conducted in refluxing ethylene glycol, which gave formation of 2‐(tert‐butyl)‐5‐nitro‐N‐phenylpyrimidin‐4‐amine (L4a) and 2‐(tert‐butyl)‐N‐(3‐(tert‐butyl)phenyl)‐5‐nitropyrimidin‐4‐amine (L4b) in high yields. Reduction of nitro substituent was executed using excessive SnCl 2 ·2H 2 O in methanol solution at RT, [ 16 ] giving isolation of 2‐(tert‐butyl)‐N 4 ‐phenylpyrimidine‐4,5‐diamine (L5a) and 2‐(tert‐butyl)‐N 4 ‐(3‐(tert‐butyl)phenyl)pyrimidine‐4,5‐diamine (L5b), after the routine workup. After then, cyclization with formic acid afforded the respective 2‐(tert‐butyl)‐9‐phenyl‐9H‐purine (L6a) and 2‐( tert ‐butyl)‐9‐(3‐(tert‐butyl)phenyl)‐9H‐purine (L6b) in high yields, according to a modified literature procedure.…”

“…[ 21 ] On the other hand, the increasing orbital overlap (between the dominant pair of orbitals contributing to the T 1 electronic transition) also results in an increased radiative rate constant due to the increased transition dipole moment. [ 16 ] The experimental results indicate that the m‐isomers achieved an greater radiative rate constant than that of the relevant f‐isomers. This might be rationalized by the greater MLCT character in the T 1 state of m‐isomers ( cf.…”

Ultrapure Blue Phosphorescent Organic Light-Emitting Diodes Employing a Twisted Pt(II) Complex

“…TE2 and TE4 exhibit long LT 50 lifetimes of 3.64 and 3.98 h at their initial luminance values of 110 and 192 cd m –2 , respectively. On the basis of exiguity for phosphorescent electroluminescent color with CIE x = 0.14, CIE y = 0.10 and 0.07, the demonstrable values achieved great progress for blue PhOLEDs. , Moreover, in consideration of the incomplete light extraction and charge utilization, efficiency and stability can possibly be boosted in the future. Additionally, EL spectra at varying viewing angles were measured at 4 mA/cm 2 to determine the spectral stability (Figures e,f and S11).…”