Emissive Osmium(II) Complexes Supported by N-Heterocyclic Carbene-based C^∧C^∧C-Pincer Ligands and Aromatic Diimines

Abstract

Osmium(II) complexes containing N-heterocyclic carbene (NHC)-based pincer ligand 1,3-bis(1-methylimidazolin-2-ylidene)phenyl anion (C(1)^C^C(1)) or 1,3-bis(3-methylbenzimidazolin-2-ylidene)phenyl anion (C(2)^C^C(2)) and aromatic diimine (2,2'-bipyridine (bpy), 1,10-phenanthroline (phen), or 4,4'-diphenyl-2,2'-bipyridine (Ph(2)bpy)) in the form of [Os(C^C^C)(N^N)(CO)](+) have been prepared. Crystal structures for these complexes show that the Os-C(NHC) bonds are essentially single (Os-C(NHC) distances = 2.079(5)-2.103(7) Å). Spectroscopic comparisons and time-dependent density functional theory (TD-DFT) calculations suggest that the lowest-energy electronic transition associated with these complexes (λ(max) = 493-536 nm, ε(max) = (5-10) × 10(3) dm(3) mol(-1) cm(-1), solvent = CH(3)CN) originate from a d(π)(Os(II)) → π*(N^N) metal-to-ligand charge transfer transition, where the d(π)(Os(II)) and π*(N^N) levels contain significant contribution from the C^C^C ligands. All these complexes are emissive in the red-spectral region (674-731 nm) with quantum yields of 10(-4)-10(-2) and emission lifetimes of around 1-6 μs. Transient absorption spectroscopy and spectroelectrochemical measurements have also been used to probe the nature of the emissive excited-states. Overall, this joint experimental and theoretical investigation reveals that the C^C^C ligands can be used to modulate the photophysical properties of a [Os(N^N)] core via the formation of the hybrid [Os + C^C^C] frontier orbitals.

A Ruthenium(II) Complex Supported by Trithiacyclononane and Aromatic Diimine Ligand as Luminescent Switch-On Probe for Biomolecule Detection and Protein Staining

“…Excitation of 1 ′ (31 μM) at 450 nm in acetonitrile resulted in an emission with λ max at 692 nm, a quantum yield of 2.334 × 10 −3 , and a lifetime of 0.272 μs. This emission was assigned as the triplet d π (Ru II ) → π*(N ∧ N) charge-transfer in nature based on comparison with analogous complexes reported previously 7 37 38 39 40 41 42 43 44 45 46 47 . The replacement of the bpy ligand with dcmb has been previously reported to red-shift the emission maximum of ruthenium(II) complexes 48 .…”

Effect of phenylamine moiety on the structure, optical properties, and phosphorescence efficiencies of some red-emitting iridium(III) complexes: A theoretical study

“…In recent decades, the photophysical properties of d 6 transition-metal complexes such as Re(I) [1,2], Ru(II) [3][4][5], Os(II) [6,7], and Ir(III) [8][9][10] have attracted enormous attention in the scientific community because of their potential applications in many areas [11,12]. Among them, the Ir(III) complexes are generally regarded as the most effective emitters in organic light-emitting diodes OLEDs [13,14] for their high phosphorescence efficiencies, high thermal stability, and relative short phosphorescent lifetime.…”

Theoretical Studies on Phosphorescent Materials: The Conjugation-Extended PtII Complexes

“…[1][2][3][4][5][6][7][8] The strong spin-orbital couplings (SOC) of the heavy-metal atom can induce an efficient intersystem crossing from the singlet to the triplet excited state, which can increase the internal quantum yields. On account of high electroluminescent quantum yields, experimental and theoretical research efforts are committed to the phosphorescent materials of Ir III complexes and their derivatives.…”