89689-85-0Relevant articles and documents
Excited-State Electron Transfer in Ligand-Bridged Dimeric Complexes of Osminum
Schanze, Kirk S.,Neyhart, Gregory A.,Meyer, Thomas J.
, p. 2182 - 2193 (1986)
The photophysical properties of the unsymmetrical ligand-bridged Os dimers, II(L)OsII(phen)(dppe)(Cl)>3+ and II(L)OsIII(phen)(dpppe)(Cl)4+ (L = 4,4'-bipyridine (4,4'bpy) or 1,2-bis(4-pyridyl)ethane (bpa), bpy = 2,2'-bipyridine, phen = 1,10-phenanthroline, and dppe = 1,2-bis(diphenylphosphino)-cis-ethene), have been investigated by using a variety of techniques.In the (II,II) dimers, two independent metal to ligand charge transfer (MLCT) chromofores are present, based upon localized d?(Os) -> phen and d?(Os) -> 2,2'-bpy transitions at the respective metal centers.The results of transient absorption and emission experiments suggest that quenching of the higher energy, Os(bpy) localized MLCT state does not occur by Os(bpy) MLCT -> Os(phen) MLCT energy transfer which is energetically favorable.Rather, the quenching may occur by reductive electron transfer from the adjacent OsII(phen) site.Rate constants for the intramolecular quenching have been measured for the bpa-bridged dimer at low temperatures in a glassy solvent.The excited-state behvior of the (II,II) dimers (L = 4,4'-bpy or bpa) is similar in frozen solutions.However, from steady-state transient emission and transient absorption data, past the glass to liquid transition the 4,4'-bpy bridging ligand in the 4,4'-bpy dimer flattens and acts as an electron acceptor.The flattening and concomitant intermolecular quenching process in fluid media are rapid compared to the lifetime of the initially populated CT excited state.In the mixed-valence (II,III) dimers the spectroscopically observed Os(bpy) MLCT excited state is relatively unperturbed by the adjacent OsIII(phen) site and there is no evidence for quenching by any of a number of energetically favorable pathways.
Synthetic routes to new polypyridyl complexes of osmium(II)
Kober, Edward M.,Caspar, Jonathan V.,Sullivan, B. Patrick,Meyer, Thomas J.
, p. 4587 - 4598 (2008/10/08)
New luminescent complexes of Os(II) that contain either 2,2′-bipyridine (bpy) or 1,10-phenanthroline (phen) as the chromophoric acceptor ligand have been prepared by a combination of established and new synthetic methods. Extensive use of Os(IV) and Os(III) precursors, e.g., OsIV(bpy)Cl4 and mer-OsIII(PMe2Ph)3Cl3, has led to the preparation of materials with ancillary ligands such as tertiary phosphines as preparative intermediates, including OsIII(bpy)(PMe2Ph)Cl3 and cis-OsII(phen)(diphosphine)Cl2. Further substitution of chloro ligands into complexes such as these results in the formation of emissive complexes of Os(II). Another new synthetic route utilizes the versatile Os(II) precursor Os(bpy)2CO3, which allows the facile preparation of dicationic, disubstituted species such as [Os(bpy)2(norbornadiene)]2+. Another general procedure, based on the control of solvent and temperature in the substitution chemistry of cis-Os(bpy)2Cl2, has been further developed to produce a variety of new complexes of the types cis-[Os(bpy)2(L)Cl]+ and cis-[Os(bpy)2(L)2]2+, where L is a phosphine, arsine, nitrogen, or olefin donor ligand. In a few cases, phosphine entering groups cause the cis geometry to be unfavorable and new trans-[Os(bpy)2(L)2]2+ complexes have also been isolated. The resultant complexes comprise the largest family of transition-metal-based excited-state reagents with tunable photophysical and redox properties available. When possible, the new complexes have been characterized by UV-visible spectroscopy, emission spectroscopy, cyclic voltammetry, and 31P and/or 1H NMR spectroscopy.
