Synthesis, Characterization, and Photophysical Properties of Os(II) Diimine Complexes [Os(N∧N)(CO)₂I₂] (N∧N = Bipyridine, Phenanthroline, and Pyridyl Benzoxazole)

Abstract

A new series of Os(II) diimine complexes with the general formula [Os(N(wedge)N)(CO)(2)I(2)], N(wedge)N = 2,2'-bipyridine (bpy) (1), 4,4'-di-tert-butyl-2,2'-bipyridine (dbubpy) (2), 4,7-diphenyl-1,10-phenanthroline (dpphen) (3), 2-(2'-pyridyl)benzoxazole (pboz) (4), and 5-tert-butyl-2-(2'-pyridyl)benzoxazole (bupboz) (5), were synthesized and characterized by spectroscopic methods and by a single-crystal X-ray diffraction study on the dpphen complex 3. The corresponding photophysical properties were studied using UV-vis and emission spectrometry. The resulting phosphorescence features both in solution and as a solid film, in combination with the MO calculation, lead us to conclude that the emissions originate from mixed halide-to-ligand (XLCT approximately 70%) and metal-to-ligand (MLCT approximately 30%) transitions instead of the typical MLCT transition. Using complexes 4 and 5 as the dopant emitters, we evaluated their potential to serve as a phosphor for organic light emitting diodes by examining their electroluminescent performances. Reddish orange electroluminescence centered around 600 nm was observed for organic light emitting diodes (OLEDs) fabricated using complex 5 as the emitter; the device efficiency was shown to be as high as 2.8% (and 5.0 cd/A or 2.7 lm/W), and the peak luminance was shown to be 5600 cd/m(2) at a driving voltage of approximately 15 V.

Osmium‐ and Ruthenium‐Based Phosphorescent Materials: Design, Photophysics, and Utilization in OLED Fabrication

“…Dicarbonyl osmium(II) complexes of the type [Os(diimine)(CO) 2 I 2 ] contain both π‐donating iodide ligands and an accepting diimine ligand with low energy π* orbitals. These osmium(II) complexes exhibit pseudo‐octahedral geometry, and the iodide and carbonyl ligands are located at the trans and cis positions, respectively 26. The main interest in initiating this investigation was to shed light on the nature of the lowest excited state; for example, whether these complexes display the basic characteristics of the usual metal‐to‐ligand charge transfer excited state (MLCT) or a state with a substantial amount of the halide‐to‐ligand charge transfer (XLCT) character.…”

Towards New Molecular Photocatalysts for CO2 Reduction: Photo‐Induced Electron Transfer versus CO Dissociation within [Os(NN)(CO)2Cl2] Complexes

“…Furthermore, in contrast to their ruthenium analogues, complexes C1 and C2 display pronounced photoluminescence properties, in the visible region, with a lifetime of few tens of nanoseconds in MeCN [16] and up to 239 ns in CH 2 Cl 2 for the diiodo [OsA C H T U N G T R E N N U N G (bpy)(CO) 2 I 2 ] derivative. [17] These observations suggest that these Os II complexes may act as the photosensitiser in a photoredox reaction. We demonstrate here that C1 and C2 undergo a net photo-induced oxidation or reduction in the presence of an irreversible electron acceptor or donor, respectively, under visible irradiation.…”

Efficient Ruthenium‐Catalyzed Aerobic Oxidation of Amines by Using a Biomimetic Coupled Catalytic System

“…For [Cu(dnbp)(DPEPhos)]BF 4 , the Stokes shift is as large as 130 nm between the maxima of the emission and the absorption (371 nm). In general, a structureless band and large Stokes shift are characteristics of a long‐range intramolecular charge transfer (CT) parentage, such as MLCT,11 XLCT,3b, 6, 7m, 12 and LLCT (ligand‐to‐ligand charge transfer)13 excited states in transition metal complexes because they are more polar than their respective ground states and subsequently induce molecular structural distortion in the excited states. The characteristic flattening distortion for a MLCT Cu(I) complex magnifies the overall distortion in the excited state and results in a further red shift of the emission band.…”