Search results for "PHOTOCHEMISTRY"
showing 10 items of 2034 documents
A Straightforward Electroactive π-Extended Tetrathiafulvalene (exTTF) Building Block
2012
The synthesis and X-ray structure of a new and readily available exTTF derivative (6) bearing a methyltriphenylphosphonium bromide moiety as a new building block for the construction of electroactive molecules is reported. The phosphonium salt 6, which was prepared in one step from 2-hydroxymethyl-exTTF as a stable yellow solid in 84 % yield, efficiently undergoes Wittig olefination reactions with a variety of aldehydes to predominantly form the E isomer. Electronic spectra and cyclic voltammetry of the novel compounds reveal the electronic communication between the electroactive units.
Environment assisted photoconversion of luminescent surface defects in SiO 2 nanoparticles
2017
Abstract Time-resolved photoluminescence investigation on SiO 2 nanoparticles was carried out in controlled atmosphere, with the aim to discern the effects induced on the typical blue luminescence band by high power UV Nd:YAG laser photons (4.66 eV) and by some selected molecular species of the air (O 2 , N 2 , CO 2 , H 2 O). These factors ultimately determine both the brightness and photostability of the emitting defect, so as to limit the unique and attracting potentialities offered by this system in many applicative fields. Here it is highlighted that the effects due to photons and molecules, singularly considered, are not additive, the radiation being more dramatic in reducing the emiss…
Thermal-, pressure- and light-induced spin-crossover behviour in the two-dimensional Hofman-like coordination polymer [Fe(3-Clpy)2Pd(CN)4]
2013
The thermal spin-crossover behaviour, photoexcitation and subsequent relaxation, as well as the pressure-induced spincrossover behaviour at 298 K are discussed for the non-porous two-dimensional Hofmann-like coordination polymer [Fe(3-Clpy)(2)Pd(CN)(4)] (1). The title compound undergoes a two-step, cooperative thermal-induced SCO with critical temperatures T-c1(down arrow) = 159.6 K and T-c1(up arrow) = 164.5 K for the first step and T-c2(down arrow) = 141.4 K and T-c2(up arrow) = 148.4 K for the second step. Irradiation of the low-spin state with green light (514 nm) at 10 K induced the photoexcitation of around 60% of the iron(II) centres to the high-spin state (LIESST effect). The subseq…
Versatility and dynamics of the copper(I) coordination sphere in sterically hindering tris(pyrazolyl)methane-incorporating macrobicycles
2009
Two arene-capped macrobicycles (1 and 2) incorporating the tris(pyrazolyl)methane (Tpm) chelate have been prepared from a benzylthiol-functionalized Tpm precursor (3). Reaction of either macrobicycle with Cu(CH3CN)4+ leads to tetrahedral or trigonal-planar, fluxional complexes incorporating the Cu(CH3CN)+ subunit ([Cu(1)(CH3CN)]+ and [Cu(2)(CH3CN)]+). The acetonitrile ancillary ligand does not fit inside the macrobicycle cavity and can be removed by heating under vacuum, which produces the [Cu(1)]+ and [Cu(2)]+ species probably involving intramolecular thioether coordination. The [Cu(1)(CH3CN)]+ complex was shown to convert slowly in wet acetone into a helical coordination polymer, which is…
A Two-State Computational Investigation of Methane C-H and Ethane C-C Oxidative Addition to [CpM(PH3)]n+ (M=Co, Rh, Ir;n=0, 1)
2006
Reductive elimination of methane from methyl hydride half-sandwich phosphane complexes of the Group 9 metals has been investigated by DFT calculations on the model system [CpM(PH(3))(CH(3))(H)] (M = Co, Rh, Ir). For each metal, the unsaturated product has a triplet ground state; thus, spin crossover occurs during the reaction. All relevant stationary points on the two potential energy surfaces (PES) and the minimum energy crossing point (MECP) were optimized. Spin crossover occurs very near the sigma-CH(4) complex local minimum for the Co system, whereas the heavier Rh and Ir systems remain in the singlet state until the CH(4) molecule is almost completely expelled from the metal coordinati…
Chemistry and reactivity of dinuclear iron oxamate complexes: alkane oxidation with hydrogen peroxide catalysed by an oxo-bridged diiron(III) complex…
2004
[EN] A new dinuclear iron(III) complex with the tetradentate ligand N,N'-o-phenylenebis(oxamate) (opba) has been synthesised, and structurally, magnetically and electrochemically characterised. It possesses an unprecedented triply bridged Fe-2(mu-O)(mu-RCO2...H2O...O2CR)(2) core, whereby two N-amides from the opba ligand complete the square-pyramidal coordination sphere of the O-carboxylate rich iron site (Fe-N = 2.053 Angstrom and Fe-O = 2.015 Angstrom), The antiferromagnetic exchange interaction between the two high-spin Fe-III ions through the oxo bridge (J = -190 cm(-1); H = -JS(1)(.)S(2)) is weaker than that found in related mu-oxo singly bridged diiron(III) complexes. The lessened ant…
Deuterated Molecular Ruby with Record Luminescence Quantum Yield
2017
The recently reported luminescent chromium(III) complex 13+ ([Cr(ddpd)2]3+; ddpd=N,N’-dimethyl-N,N’-dipyridine-2-yl-pyridine-2,6-diamine) shows exceptionally strong near-IR emission at 775 nm in water under ambient conditions (F=11%) with a microsecond lifetime as the ligand design in 13+ effectively eliminates non-radiative decay pathways, such as photosubstitution, back-intersystem crossing, and trigonal twists. In the absence of energy acceptors, such as dioxygen, the remaining decay pathways are energy transfer to high energy solvent and ligand oscillators, namely OH and CH stretching vibrations. Selective deuteration of the solvents and the ddpd ligands probes the efficiency of these o…
Ammonia Activation by a Nickel NCN-Pincer Complex featuring a Non-Innocent N-Heterocyclic Carbene: Ammine and Amido Complexes in Equilibrium
2015
A Ni0-NCN pincer complex featuring a six-membered N-heterocyclic carbene (NHC) central platform and amidine pendant arms was synthesized by deprotonation of its NiII precursor. It retained chloride in the square-planar coordination sphere of nickel and was expected to be highly susceptible to oxidative addition reactions. The Ni0 complex rapidly activated ammonia at room temperature, in a ligand-assisted process where the carbene carbon atom played the unprecedented role of proton acceptor. For the first time, the coordinated (ammine) and activated (amido) species were observed together in solution, in a solvent-dependent equilibrium. A structural analysis of the Ni complexes provided insig…
Structural and surface characterization of the polycrystalline system CrxOy · TiO2 employed for photoreduction of dinitrogen and photodegradation of …
1992
The polycrystalline system CrxOy-TiO2, used as a catalyst for photoreactions, was studied by X-ray diffractometric method, visible-ultraviolet diffuse reflectance and infrared spectroscopic methods, surface area determination, and porosimetry to characterize its structural and surface features. Two series of catalysts were prepared by two different methods, namely by coprecipitation and by impregnation. The first series was tested as photocatalysts for the dinitrogen photoreduction in a gas-solid regime and for the phenol photodegradation in a liquid-solid regime. The results indicate that the interaction of chromium ions with OH groups modifies the surface properties of the supports and co…