Search results for "transition-metal"
showing 10 items of 24 documents
The first example of cofacial bis(dipyrrins)
2016
International audience; Two series of cofacial bis(dipyrrins) were prepared and their photophysical properties as well as their bimolecular fluorescence quenching with C-60 were investigated. DFT and TDDFT computations were also performed as a modeling tool to address the nature of the fluorescence state and the possible inter-chromophore interactions. Clearly, there is no evidence for such interactions and the bimolecular quenching of fluorescence, in comparison with mono-dipyrrins, indicates that C-60-bis(dipyrrin) contacts occur from the outside of the "mouth" of the cofacial structure.
Preparation, Characterization, and Photoactivity of Polycrystalline Nanostructured TiO2 Catalysts.
2004
Various preparations of nanostructured TiO2 starting from Ti(iso-OC3H7)4 or TiCl4 are reported. The samples were characterized by X-ray diffractometry, specific surface area and porosity determinations, scanning and transmission electron microscopy, and diffuse reflectance spectroscopy. 4-Nitrophenol photodegradation in aqueous medium was employed as a probe reaction to test the photoactivity of the catalysts. The photoactivity of some samples derived from Ti(iso-OC3H7)4 was found comparable with that of commercial powders. Calcination after the hydrolysis process was necessary to achieve crystallization of the particles before using them as photocatalysts for the reaction studied. The samp…
Cobalt Electrolyte/Dye Interactions in Dye-Sensitized Solar Cells: A Combined Computational and Experimental Study
2012
We report a combined experimental and computational investigation to understand the nature of the interactions between cobalt redox mediators and TiO2 surfaces sensitized by :ruthenium and organic dyes, and their impact on. the performance of the corresponding dye-sensitized solar cells (DSSCs). We : focus: on different ruthenium dyes and fully organic dyes, to understand the dramatic loss of efficiency observed for the prototype Ru(II) N719 dye in conjunction with :Cobalt: electrolytes. Both N719- and Z907-based DSSCs showed an increased lifetime in iodine-based electrolyte compared to the cobalt-based redox-shuttle; While the organic D21L6 and D25L6 cycles endowed.With long alkoxy chains,…
Exchange coupling in the correlated electronic states of amorphous GdFe films
2013
The bulk sensitivity of hard x-ray photoelectron spectroscopy in combination with circularly polarized radiation of the P09 beamline at PETRA III enables the investigation of the magnetic properties of capped films. We have determined the temperature dependence of the magnetic circular dichroism in the Fe 2$p$ and in the Gd 3$d$ states in amorphous GdFe films. The magnetic dichroism reflects the stronger temperature dependence of Gd moments compared to Fe moments in agreement with mean-field models. We resolved the exchange split Gd 3${d}_{5/2}$ substates and found a significant temperature dependence of the splitting which is attributed to a temperature dependent part of the exchange energ…
From magnetic to nonlinear optical switches in spin-crossover complexes
2013
ISI Document Delivery No.: 109TF Times Cited: 0 Cited Reference Count: 173 Lacroix, Pascal G. Malfant, Isabelle Real, Jose-Antonio Rodriguez, Vincent Wiley-v c h verlag gmbh Weinheim Si; Various attempts to combine magnetic and nonlinear optical (NLO) properties in a molecule are reviewed, with a special focus on the possibility of interplay between the magnetic component and the quadratic (proportional to E-2) NLO response. This multidisciplinary research leads to the idea of spin-crossover-induced (SCO-induced) NLO switching and is evaluated at the synthetic level, with insights provided by computational chemistry. The need for nontraditional experimental setups to record NLO properties i…
Syntheses, Structures, Magnetic Properties, and Density Functional Theory Magneto-Structural Correlations of Bis(μ-phenoxo) and Bis(μ-phenoxo)-μ-acet…
2013
The bis(mu-phenoxo) (FeNiIII)-Ni-II compound [Fe-III(N-3)(2)LNiII(H2O)(CH3CN)](ClO4) (1) and the bis(mu-phenoxo)-mu-acetate/bis(mu-phenoxo)-bis(mu-acetate) (FeNiII)-Ni-III compound {[Fe-III(OAc)LNiII(H2O)(mu-OAc)](0.6)center dot[(FeLNiII)-L-III(mu-OAc)(2)](0.4)}(ClO4)center dot 1.1H(2)O (2) have been synthesized from the Robson type tetraiminodiphenol macrocyclic ligand H2L, which is the [2 + 2] condensation product of 4-methyl-2,6-diformylphenol and 2,2'-dimethy1-1,3-diaminopropane. Single-crystal X-ray structures of both compounds have been determined. The cationic part of the dinuclear compound 2 is a cocrystal of the two species [Fe-III(OAc)LNiII(H2O)(mu-OAc)](+) (2A) and [(FeLNiII)-L-I…
DETECTION LIMITS FOR NATURAL CIRCULAR-DICHROISM OF CHIRAL COMPLEXES IN THE X-RAY RANGE
1993
Whereas both Magnetic Circular Dichroism and Faraday Rotation studies have been successfully carried out at the K-, L- and M-absorption edges of metal atoms in ferromagnetic systems, Natural optical activity of chiral complexes has not yet been detected quite unambiguously in the X-ray range. We review a number of theoretical arguments which confirm that the optical asymmetry factor gσ should be very small in the X-ray range for unoriented powdered samples, especially at the K-absorption edges. This stimulating challenge prompted us to start an intensive programme of measurements aimed at detecting natural circular dichroism in both the soft and “firm” X-ray ranges. Although some of our ex…
Ligand-Based Charge-Transfer Luminescence in Ionic Cyclometalated Iridium(III) Complexes Bearing a Pyrene-Functionalized Bipyridine Ligand: A Joint T…
2012
Two new heteroleptic iridium(III) complexes [Ir(ppy)(2)(pyr(2)bpy)][PF(6)] ([1a][PF(6)]) and [Ir(dfppy)(2)(pyr(2)bpy)][PF(6)] ([2a][PF(6)]), where Hppy = 2-phenylpyridine, Hdfppy = 2-(3,5-difluorophenyl)pyridine, and pyr(2)bpy = 5,5'-bis(pyren-1-yl)-2,2'-bipyridine, have been synthesized and fully characterized. The single-crystal structures of pyr(2)bpy and the complexes 4{[1a][PF(6)]}·2CH(2)Cl(2)·9H(2)O and [2a][PF(6)]·0.25CH(2)Cl(2)·H(2)O have been determined. The effect of the pyrene substituents on the electronic properties is investigated through a comprehensive photophysical and theoretical study on the two complexes in comparison to reference complexes without substituents on the an…
Photophysical Properties of Charged Cyclometalated Ir(III) Complexes: A Joint Theoretical and Experimental Study
2011
The photophysical properties of a series of charged biscyclometalated [Ir(ppy)(2)(N boolean AND N)](1+) complexes, where ppyH is 2-phenylpyridine and N boolean AND N is 2,2'-bipyridine (bpy), 6-phenyl-2,2'-bipyridine (pbpy), and 6,6'-dipheny1-2,2'-bipyridine (dpbpy) for complexes 1, 2, and 3, respectively, have been investigated in detail. The photoluminescence performance in solution decreases from 1 to 3 upon attachment of phenyl groups to the ancillary ligand. The absorption spectra recorded over time suggest that complex 3 is less stable compared to complexes 1 and 2 likely due to a nucleophilic-assisted ancillary ligand-exchange reaction. To clarify this behavior, the temperature depen…
Strain Release Chemistry of Photogenerated Small‐Ring Intermediates
2021
Abstract Photochemical processes, such as isomerizations and cycloadditions, have proven to be very useful in the construction of highly strained molecular frameworks. Photoinduced ring strain enables subsequent exergonic reactions which do not require the input of additional chemical energy and provides a variety of attractive synthetic options leading to complex structures. This review covers the progress achieved in the application of sequences combining excitation by ultraviolet light to form strained intermediates, which are further transformed to lower energy products in strain‐release reactions. As ring strain is considerable in small ring systems, photogenerated three‐ and four‐memb…