Emissive osmium(II) complexes supported by N-heterocyclic carbene-based C^C^C-pincer ligands and aromatic diimines

Research output: Journal Publications and Reviews (RGC: 21, 22, 62)21_Publication in refereed journalpeer-review

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Detail(s)

Original languageEnglish
Pages (from-to)8693-8703
Journal / PublicationInorganic Chemistry
Volume51
Issue number16
Online published8 Aug 2012
Publication statusPublished - 20 Aug 2012

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 2bpy)) 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 ( max = 493-536 nm, μ max = (5-10)×10 3 dm 3 mol -1 cm -1, solvent = CH 3CN) 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. 

Research Area(s)

  • TRANSITION-METAL-COMPLEXES, SOLAR-ENERGY CONVERSION, COORDINATION-COMPOUNDS, NHC LIGANDS, POLYPYRIDYL COMPLEXES, IRIDIUM COMPLEXES, EXCITED-STATES, ORGANOMETALLIC CATALYSIS, PHOTOPHYSICAL PROPERTIES, ALLENYLIDENE COMPLEXES