Role of the Diphosphine Chelate in Emissive, Charge‐Neutral Iridium(III) Complexes

Abstract

A class of neutral tris-bidentate Ir metal complexes incorporating a diphosphine as a chelate is prepared and characterized here for the first time. Treatment of [Ir(dppBz)(tht)Cl ] (1, dppBz=1,2-bis(diphenylphosphino)benzene, tht=tetrahydrothiophene) with fppzH (3-trifluoromethyl-5-(2'-pyridyl)-1H-pyrazole) afforded the dichloride complexes, trans-(Cl,Cl)[Ir(dppBz)(fppz)Cl ] (2) and cis-(Cl,Cl)[Ir(dppBz)(fppz)Cl ] (3). The reaction of 3 with the dianionic chelate precursor, 5,5'-di(trifluoromethyl)-3,3'-bipyrazole (bipzH ) or 5,5'-(1-methylethylidene)-bis(3-trifluoromethyl-1H-pyrazole) (mepzH ), in DMF gave the tris-bidentate complex [Ir(dppBz)(fppz)(bipz)] (4) or [Ir(dppBz)(fppz)(mepz)] (5), respectively. In contrast, a hydride complex [Ir(dppBz)(fppz)(bipzH)H] (6) was isolated instead of 4 in protic solvent, namely: diethylene glycol monomethyl ether (DGME). All complexes 2-6 are luminescent in powder form and thin films where the dichlorides (2, 3) emit with maxima at 590-627 nm (orange) and quantum yields (QYs) up to 90 % whereas the tris-bidentate (4, 5) and hydride (6) complexes emit at 455-458 nm (blue) with QYs up to 70 %. Hybrid (time-dependent) DFT calculations showed considerable metal-to-ligand charge transfer contribution to the orange-emitting 2 and 3 but substantial ligand-centered π-π* transition character in the blue-emitting 4-6. The dppBz does not participate in the radiative transitions in 4-6, but it provides the rigidity and steric bulk needed to promote the luminescence by suppressing the self-quenching in the solid state. Fabrication of an organic light-emitting diode (OLED) with dopant 5 gave a deep-blue CIE chromaticity of (0.16, 0.15). Superior blue emitters, which are vital in OLED applications, may be found in other neutral Ir complexes containing phosphine chelates.

Iridium(III) Complexes Bearing a Formal Tetradentate Coordination Chelate: Structural Properties and Phosphorescence Fine-Tuned by Ancillaries

“…As for a possible reaction pathway, the hydrides of both 7 and 8 may be derived from the hydroxyl group of a protic solvent employed in the present studies, for which the employed conditions are akin to many transformations documented in the literature. 51,52 We have also tried to confirm this possibility by using isotope tracing, i.e., the addition of D 2 O into the reaction mixture. However, the introduction of a small amount of D 2 O has failed to incorporate enough deuteride in the final product, but too much D 2 O caused a complete suppression of product formation, giving no answer to their origins.…”

Fluorinated Pyrazoles: From Synthesis to Applications

“…Indeed, with the development of novel synthetic methods, the repertoire of fluorinated pyrazole ligands has increased dramatically in recent years. It is impossible to consider in this review each individual example in detail, but the list of structures with fluorinated pyrazoles prepared during the past 5 years and brief descriptions of their applications with references are outlined in Figure . − …”

Preparation, Characterization, and Electrochemical Activation of a Model [Cp*Rh] Hydride

“…For comparison, the free dppb ligand is reduced at a more negative potential, 53 while other metal complexes of dppb do not manifest ligand-centered reductions at relevant potentials. 54,55 Our proposal is also consistent with electrochemical studies of the related [Cp*Rh-(bpy)Me] + complex, which undergoes both quasi-reversible diimine-centered reduction (E 1/2 = −1.78 V) and metalcentered reduction (E p,c = −2.22 V), as demonstrated by chemical and spectroscopic studies. 40 And although we have not investigated the mechanism of H 2 generation from this system further, we note that a bimolecular pathway leading to H 2 generation with 3 via bond homolysis of a transient [Rh II − H] species would be reminiscent of Wayland's generation of [Rh III −H] 2 species by treatment of bimetallic [Rh II 2 ] complexes with H 2 .…”