The series of osmium(ii) complexes [Os(bpy)3-n(btz)n][PF6]2 (bpy = 2,2'-bipyridyl, btz = 1,1'-dibenzyl-4,4'-bi-1,2,3-triazolyl, n = 0, n = 1, n = 2, n = 3), have been prepared and characterised. The progressive replacement of bpy by btz leads to blue-shifted UV-visible electronic absorption spectra, indicative of btz perturbation of the successively destabilised bpy-centred LUMO. For , a dramatic blue-shift relative to the absorption profile for is observed, indicative of the much higher energy LUMO of the btz ligand over that of bpy, mirroring previously reported data on analogous ruthenium(ii) complexes. Unlike the previously reported ruthenium systems, heteroleptic complexes and display intense emission in the far-red/near-infrared (λmax = 724 and 713 nm respectively in aerated acetonitrile at RT) as a consequence of higher lying, and hence less thermally accessible, (3)MC states. This assertion is supported by ground state DFT calculations which show that the dσ* orbitals of to are destabilised by between 0.60 and 0.79 eV relative to their Ru(ii) analogues. The homoleptic complex appears to display extremely weak room temperature emission, but on cooling to 77 K the complex exhibits highly intense blue emission with λmax 444 nm. As complexes to display room temperature luminescent emission and readily reversible Os(ii)/(iii) redox couples, light-emitting electrochemical cell (LEC) devices were fabricated. All LECs display electroluminescent emission in the deep-red/near-IR (λmax = 695 to 730 nm). Whilst devices based on and show inferior current density and luminance than LECs based on , the device utilising shows the highest external quantum efficiency at 0.3%.
Fundamental insights into the mechanism of triplet excited state interligand energy transfer dynamics and origin of dual emission for phosphorescent iridium(III) complexes are presented. The complexes [Ir(C^N) 2 (N^N)] + (HC^N = 2-phenylpyridine (1a-c), 2-(2,4-difluorophenyl)pyridine (2a-c), 1-benzyl-4-phenyl-1,2,3-triazole (3a-c); N^N = 1-benzyl-4-(pyrid-2-yl)-1,2,3-triazole (pytz, a), 1-benzyl-4-(pyrimidin-2-yl)-1,2,3-triazole (pymtz, b), 1-benzyl-4-(pyrazin-2-yl)-1,2,3-triazole (pyztz, c)) are phosphorescent in room temperature fluid solutions from triplet metal-to-ligand charge transfer
Whilst [Os(N^N)3 ](2+) complexes are supposed to be photochemically inert to ligand loss, the complex [Os(btz)3 ](2+) (btz=1,1'-dibenzyl-4,4'-bi-1,2,3-triazolyl) undergoes unprecedented photolytic reactivity to liberate free btz (Φ363 ≈1.2 %). Further, both cis and trans isomers of the photodechelated ligand-loss solvento intermediate [Os(κ(2) -btz)2 (κ(1) -btz)(NCMe)](2+) are unambiguously observed and characterized by NMR spectroscopy and mass spectrometry.
A new “click” ligand, 2,6-bis(1-(pyridin-4-ylmethyl)-1H-1,2,3-triazol-4-yl)pyridine (L) featuring a tridentate 2,6-bis(1,2,3-triazol-4-yl)pyridine (tripy) pocket and two pyridyl (py) units was synthesized in modest yield (42%) using the copper(I) catalyzed azide-alkyne cycloaddition (CuAAC) reaction. The coordination chemistry of the ligand with silver(I) and iron(II) ions was examined using a battery of solution (1H and DOSY (diffusion ordered spectroscopy) nuclear magnetic resonance (NMR), infrared and absorption spectroscopies, high-resolution electrospray ionization mass spectrometry (HR-ESI-MS)), and solid state (X-ray crystallography, elemental analysis) techniques. When treated with silver(I) ions, the ligand forms discrete [Ag(L)]+ (X−, where X− = BF4−, NO3− or SbF6−) complexes in dimethyl sulfoxide (DMSO) solution but these complexes crystallize as coordination polymers. The addition of [Fe(H2O)6](BF4)2 to an acetonitrile solution of the ligand forms the expected monomeric octahedral [Fe(L)2]2+ complex and treatment of the iron(II) complex with AgBF4 generates a heterometallic linear coordination polymer.
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