86,609 research outputs found
Photoinduced energy transfer in a fullerene-oligophenylenevinylene conjugate
No full textA fullerene derivative in which two oligophenylenevinylene (OPV) groups are attached to C60 through a pyrrolidine ring has been prepared and photophysical studies in CH2Cl2 solution show that photoinduced energy transfer from the OPV moieties to C60 occurs, and not electron transfer
A fulleropyrrolidine with two oligophenylenevinylene substituents: Synthesis, electrochemistry and photophysical properties
No full textA fullerene derivative in which two oligophenylenevinylene (OPV) groups are attached to C60 through a pyrrolidine ring has been prepared and photophysical studies in CH2Cl2 solution show that photoinduced energy transfer from the OPV moieties to C60 occurs, and not electron transfer. On passing to a more polar solvent such as benzonitrile, again no evidence of electron transfer is found
Spectroscopy and electrochemical properties of a homologous series of acetylacetonato and hexafluoroacetylacetonato cyclopalladated and cycloplatinated Complexes
No full textA photophysical, electrochemical and computational study has been performed on a homologous series
of cyclometallated Pd(II) (1a–f) and Pt(II) (2a–f) complexes of general formula [(C,N)M(O,O)];
(H(C,N) = azobenzene, 2-phenylpyridine, benzo[h]quinoline; M = Pd, Pt; H(O,O) = acetylacetone,
hexafluoroacetylacetone). Experimental and computational data have shown the strong influence
exerted by electronegativity of the ancillary ligand on the frontier orbitals of the complexes, such an
effect being enhanced for the Pt(II) species
Synthesis, complexation and photophysics in protic solvents of lanthanide complexes of novel calix[4]arene polycarboxylic-2,2'-bipyridine mixed ligands
No full textTwo novel cone calix[4]arene ligands 11a and 11b bearing two iminodiacetic chelating units and two C-6 or C substituted 2,2'-bipyridine chromophores in diametral position at the lower rim were synthesized. These ligands form complexes with lanthanide ions in methanol solution whose stability (4.5 < log K-ass < 6.2) depends on the substitution pattern (C-6 or C-5) of the 2,2'-bipyridine units. Contrary to that observed with other neutral calixarene ligands, the luminescence properties of the Eu3+ and Tb3+ complexes are not very much affected by the type of the 2,2'-bipyridine chromophore. Luminescence lifetimes (0.31 ms < tau < 1.1 ms) and quantum yields (0.017 < phi < 0.130) are higher for Terbium compared with the corresponding Europium complexes
Excited-State Properties in Supramolecular Systems. Luminescence and Intercomponent Interactions in a 3-Catenand and Some 3-Catenates
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Photoinduced Energy and Electron Transfer Processes in Supramolecular Species. Tris(bipyridine) Complexes of Ru(II)/Os(II), Ru(II)/Ru(III), Os(II)/Os(ITI), and Ru(II)/Os(III) Separated by a Rigid Spacer
No full textThe bis(bipyridine) bridging ligand 1,4-bis[2-(2,2′-bipyridin-5-yl)ethenyl]bicyclo[2.2.2]octane(bpy-S-bpy), where S is a rigid spacer made of a bicyclooctane unit symmetrically linked to two ethylene-type units in a E,E-configuration, has been synthesized and its complexes (bpy)2Ru(bpy-S-bpy)2+ (RuII·A), (bpy)2Os(bpy-S-bpy)2+ (OsII·A), (bpy)2-Ru(bpy-S-bpy)Ru(bpy)24+ (RuII·A·RuII), (bpy)2Os(bpy-S-bpy)Os(bpy)24+ (OsII·AII·OsII), (bpy)2Ru(bpy-S-bpy)-Os(bpy)24+ (RuII·A·OsII) have been prepared as PF6- salts. The length of the rigid spacer S is 9 Å, and the center-to-center separation distance in the dinuclear complexes is 17 Å. In all these novel compounds, each Ru-based and Os-based unit displays its own absorption spectrum and electrochemical properties, regardless of the presence of a second metal-based unit. The homometallic dinuclear compounds exhibit the same luminescence properties as the corresponding mononuclear species, whereas in the heterometallic dinuclear RuII·A·OsII species 91% of the Ru-based luminescence intensity is quenched by energy transfer to the Os-based unit, whose luminescence is accordingly sensitized (acetonitrile solution, room temperature). The excited state lifetime of the Ru-based unit (209 ns) is reduced to 18 ns, and a comparable risetime is observed for the energy transfer sensitization of the Os-based luminescence. The energy transfer process occurs with rate constant 5.0 × 107 s−1, predominantly by an exchange mechanism. Partial oxidation of the binuclear species RuII·A·RuII, OsII·A·OsII, and RuII·A·OsII by Ce(I V) in acetonitrile-water solutions leads to mixed-valence MII·A·MIII species (M = Ru and/or Os) where the oxidized metal-based unit quenches the luminescent excited state of the unit that is not oxidized. For the RuII·A·OsIII compound, the residual luminescent intensity of the Ru-based unit is <1.5% and its excited state lifetime is 115 ps. The quenching occurs by electron transfer (kel = 8.7 × 109 s−1) with formation of the thermodynamically unstable RuIII·A·OsII valence isomer which then goes back (kb = 1.0 × 106 s−1) to RuII·A·OsIII. The RuII·A·RuIII and OsII·A·OsIII mixed-valence compounds can only be obtained in the presence of the corresponding MII·A·MII and MIII·A·MIII species, according to a statistical distribution. For both the homometallic mixed-valence compounds the quenching of the luminescence intensity of the nonoxidized unit by the oxidized one is larger than 90%. Lifetime measurements have shown that the quenching rate constant is 1.1 × 109 s−1 for RuII·A·RuIII and 5.0 × 109 s−1 for OsII·A·OsIII. The quenching process takes place by an electron transfer mechanism. The parameters which govern the rates of the energy and electron transfer processes in this homogeneous family of compounds are discussed in the light of current theories. It is shown that the electronic matrix element is ∼0.6 cm−1 for the energy transfer process in *RuII·A·OsII, ∼7–10 cm−1 for the electron transfer processes in *RuII·A·OsIII, *RuII·A·RuII, and *OsII·A·OsIII, and ∼ 1.0 cm−1 for the (back) electron transfer process in RuII·A·OsII
Rigid rodlike dinuclear Ru/Os complexes of a novel bridging ligand. Intercomponent energy and electron-transfer processes
No full textThe PF6- salts of the dinuclear complexes [(bpy)2Ru(PAP)Ru(bpy)2]4+ (RuIIPAPRuII), [(bpy)2Os(PAP)Os-(bpy)2]4+ (OsIIPAPOsII), and [(bpy)2Ru(PAP)Os(bpy)2]4+ (RuIIPAPOsII) have been prepared, where bpy = 2,2′-bipyridine and PAP is a rodlike bridging ligand made of an adamantane-based spacer collinear with the coordination axis of two 1,10-phenanthroline units. In the prepared complexes, the metal - metal distance is 2.1 nm. In the RuIIPAPOsII compound, photoinduced energy transfer from the RuII-based to the OsII-based unit takes place with rate constant 5.2 × 107 s-1 at room temperature and 2.4 × 107 s-1 at 77 K. In the mixed-valence RuIIPAPOsIII compound, the luminescent excited state of the RuII-based unit is quenched via electron transfer by the OsIII-based unit with rate constant 7.2 × 106 s-1. The rate constant for the backelectron-transfer reaction is 8.3 × 103 s-1
Design of luminescent lanthanide complexes: From molecules to highly efficient photo-emitting materials
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