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| 2. |
- Börje, Anna, 1961, et al.
(författare)
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New luminescent and redox-active mono- and polynuclear ruthenium(II) and osmium(II) polypyridine complexes
- 2002
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Ingår i: Journal of the Chemical Society-Dalton Transactions. - 1472-7773. ; :6, s. 843-848
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Tidskriftsartikel (refereegranskat)abstract
- A series of mono and polynuclear Ru(II) and Os(II) polypyridine complexes based on the bpy-O-bpy ligand {bpy-O-bpy = bis[4-(2,2'-bipyridinyl)]ether} has been prepared. The redox, absorption and luminescence properties of these species have been measured and compared with those of the [Ru(bpy)(3)](2+) and [Os(bpy)(3)](2+) parent compounds. Electrochemical oxidation involves the metal centers, and occurs reversibly in acetonitrile at room temperature at about +1.30 and +0.85 V vs. SCE, respectively, for the Ru- and Os-based units. Reduction is ligand-centered and features a first irreversible wave followed by several reversible processes. Absorption spectra are essentially the sum of the spectra of the component monometallic species. Luminescence emission is observed both in acetonitrile solution (298 K) and in frozen matrix (77 K), originating from (MLCT)-M-3 states. Homometallic complexes display luminescence properties which are close to that featured by the parent [M(bpy)(3)](2+) species. In heterometallic species luminescence is observed only from the Os-based unit, indicating that efficient energy transfer takes place from the Ru-based to the Os-based moiety. The results indicate that the electronic communication through the bpy-O-bpy bridging ligand is so small that it doesn't substantially modify the properties of the metal units, which are those of the corresponding isolated [M(bpy)(3)](2+) units, but large enough to allow efficient energy transfer through the bridge. The bpy-O-bpy bridging ligand appears thus a promising component for the synthesis of multimetallic antenna systems.
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| 4. |
- Ghazzali, Mohamed I D M, 1974, et al.
(författare)
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Syntheses, crystal structures, optical limiting properties, and DFT calculations of three thiophene-2-aldazine Schiff base derivatives
- 2007
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Ingår i: New Journal of Chemistry. - : Royal Society of Chemistry (RSC). - 1369-9261 .- 1144-0546. ; 31:10, s. 1777-1784
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Tidskriftsartikel (refereegranskat)abstract
- The syntheses, characterizations and structural determinations of N,N'-bis(thiophenyl-2-methylene)hydrazine 1, N,N'-bis(4-bromothiophenyl-2-methylene)hydrazine 2 and N,N'-bis(5-bromothiophenyl-2-methylene)hydrazine 3 are presented. The materials show third-ordernonlinear behaviour with transmissions of 20, 22 and 18 μJ for an input energy of 150 μJ. The4- and 5-bromothiophenic structures show Br...Br interactions of 3.562 and 3.626 Å, respectively.Analysis of bromine containing aromatic compounds in the Cambridge CrystallographicDatabase (CSD) showed the expected angle dependences of the Br...Br interactions dividing theseinto ‘‘type I’’ and ‘‘type II’’. A semi-quantitative agreement was found between the CSD data anda model derived form calculated electrostatic potentials.
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| 5. |
- Gejke, Cecilia, 1973, et al.
(författare)
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The effect of lithium insertion on the structure of tin oxide-based glasses
- 2001
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Ingår i: Journal of Power Sources. - 0378-7753. ; 97-98, s. 226-228.
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Tidskriftsartikel (refereegranskat)abstract
- Two different SnO-based glasses, Sn2B3O6.5 and Sn2B2AlO6.5, have been examd. with FT-IR and Raman spectroscopy at different stages during the first electrochemical cycle. Some disruption of the connection between borate units in the network occurred during cycling. There was also an irreversible formation of Li3BO3 that can be related to the large capacity loss.
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| 7. |
- Börjesson, Karl, 1982, et al.
(författare)
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Nucleic Acid Base Analog FRET-Pair Facilitating Detailed Structural Measurements in Nucleic Acid Containing Systems
- 2009
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 1520-5126 .- 0002-7863. ; 131:12, s. 4288-4293
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Tidskriftsartikel (refereegranskat)abstract
- We present the first nucleobase analog fluorescence resonance energy transfer (FRET)-pair. The pair consists of tC O , 1,3-diaza-2- oxophenoxazine, as an energy donor and the newly developed tC nitro , 7-nitro-1,3-diaza-2-oxophenothiazine, as an energy acceptor. The FRET-pair successfully monitors distances covering up to more than one turn of the DNA duplex. Importantly, we show that the rigid stacking of the two base analogs, and consequently excellent control of their exact positions and orientations, results in a high control of the orientation factor and hence very distinct FRET changes as the number of bases separating tC O and tCnitro is varied. A set of DNA strands containing the FRET-pair at wisely chosen locations will, thus, make it possible to accurately distinguish distance- from orientation-changes using FRET. In combination with the good nucleobase analog properties, this points toward detailed studies of the inherent dynamics of nucleic acid structures. Moreover, the placement of FRET-pair chromophores inside the base stack will be a great advantage in studies where other (biomacro)molecules interact with the nucleic acid. Lastly, our study gives possibly the first truly solid experimental support to the dependence of energy transfer efficiency on orientation of involved transition dipoles as predicted by the Forster theory. © 2009 American Chemical Society.
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| 8. |
- Fortage, Jerome, et al.
(författare)
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Charge transfer state and large first hyperpolarizability in a highly electronically coupled zinc and gold porphyrin dyad
- 2009
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Ingår i: Chemistry - A European Journal. - 1521-3765 .- 0947-6539. ; 15:36, s. 9058-9067
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Tidskriftsartikel (refereegranskat)abstract
- We report the synthesis and the characterizations of a novel dyad composed of a zinc porphyrin (ZnP) linked to a gold porphyrin (AuP) through an ethynyl spacer. The UV/Vis absorption spectrum and the electrochemical properties clearly reveal that this dyad exhibits a strong electronic coupling in the ground state as evidenced by shifted redox potentials and the appearance of an intense charge-transfer band localized at lambda = 739 nm in dichloromethane. A spectroelectrochemical study of the dyad along with the parent homometallic system (i.e., ZnP-ZnP and AuP-AuP) was undertaken to determine the spectra of the reduced and oxidized porphyrin units. Femtosecond transient absorption spectroscopic analysis showed that the photoexcitation of the heterometallic dyad leads to an ultrafast formation of a charge-separated state (+ZnP-AuP center dot) that displays a particularly long lifetime (tau=4 ns in toluene) for such a short separation distance. The molecular orbitals of the dyad were determined by DFT quantum-chemical calculations. This theoretical study confirms that the observed intense band at lambda = 739 nm corresponds to an interporphyrin charge-transfer transition from the HOMO orbital localized on the zinc porphyrin to LUMO orbitals localized on the gold porphyrin. Finally, a Hyper-Rayleigh scattering study shows that the dyad possesses a large first molecular hyperpolarizability coefficient (beta = 2100 x 10(-30) esu at lambda = 1064 nm), thus highlighting the valuable nonlinear optical properties of this new type of push-pull porphyrin system.
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| 9. |
- Johnson, J.R.T, et al.
(författare)
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Water adsorption and hydrolysis in the Si2O4, P2O5 and P4O10 systems - essential roles of the phosphate system in biosynthesis
- 2002
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Ingår i: Chemical Physics. - 0301-0104. ; 276:1, s. 45-68
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Tidskriftsartikel (refereegranskat)abstract
- Successive water addition to the mononuclear species SiO2(g) and PO2(OH)(g), as well as the corresponding binuclear Si2O4(g) and P2O5(g) molecules, is studied by means of density functional theory. Hydrolysis of (HO)3SiOSi(OH)3(g) is found to be slightly endothermic, and only an asymmetric energy minimum is found for this silicic acid dimer. Four stable conformations are determined for the pyrophosphoric acid system (HO)2OPOPO(OH)2(g). Depending on the choice of reference structure and basis set, the hydrolysis energetics ranges from 14–26 kJ/mol exothermic to 3–7 kJ/mol endothermic. In general, the hydrolysis reaction is best described as a near zero-energy process. Significant differences in the water chemistry of the final monomeric products, Si(OH)4(g) and PO(OH)3(g), appear in the first solvation shell. Connecting the P–OH and P=O groups by water bridges results in a greater tendency for proton delocalization in PO(OH)3(g), than is observed when water is used to connect two Si–OH groups in Si(OH)4(g). Taking the properties of pyrophosphoric acid as model for the P–O–P bridge in adenosine triphosphate (ATP), the results of the present study support the notion that this molecule and its hydrolysis products provide a nano-scale buffer, which is essential for sustaining biosynthesis by controlling the proton and water activities.
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| 10. |
- Johnson, J.R.T, et al.
(författare)
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Water adsorption and hydrolysis on molecular Al oxides and hydroxides - solvation versus cluster formation
- 2001
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Ingår i: Physical Chemistry Chemical Physics. - 1463-9084 .- 1463-9076. ; 3:24, s. 5482-5488
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Tidskriftsartikel (refereegranskat)abstract
- Addition of water to the AlO(OH)(g) molecule and to the corresponding binuclear anhydride Al2O3(g) are studied by means of quantum chemistry. The AlO bond and the Al–O–Al bridge are found to be highly reactive towards water, and the final products are determined as Al(OH)3(g) and the dimer Al2(OH)6(g). The addition of further H2O molecules to Al(OH)3(g) was used to model micro-solvation. Two different types of cluster structures are found for Al(OH)3·nH2O. One type contains an Al(OH)4−/H3O+ ion-pair, for which the core anion displays a four-coordinated geometry on Al. The second type displays a six-coordinate Al, while tending to form a cationic core. Both structures require a Al(OH)3·6H2O(g) system as computational model to be observed. For neutral environments, polymerization of Al(OH)3 is preferred over the solvation of monomeric species. The results are understood to reflect the amphoteric dissolution chemistry of aluminium hydroxide under acidic or alkaline conditions.
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