Electrogenerated chemiluminescence: A molecular electrochemistry point of view

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Preparation and crystal structure of bis(protonated 2,6-diacetylpyridine bis(phenylhydrazone)) uranyl tetrachloride,CH3CN

The reaction of 2,6-diacetylpyridine-bis(phenylhydrazone),L, with commercial uranyl chloride under a variety of different conditions gave only complexes of the type [2LH]²⁺[UO₂Cl₄]^2?,xCH₃CN (x = 1 or 2). The structure of the title compound was determined by X-ray analysis. The crystals are triclinic, space groupP¯1,a=12.77(1),b= 23.12(2),c= 8.11(1) Å, α = 94.33(3) °, β = 89.43(3) °, γ = 98.22(3) ° andZ= 2. The structure was solved by Fourier methods, and refined by least-squares toR= 0.074 for 5210 reflections which were measured on an automatic diffractometer. The [UO₂Cl₄]^2? anions have approximately^4mm _m (D _4h ) symmetry, with the uranyl group perpendicular to a plane in which the four chlorine atoms occupy the corners of a square. The organic cations are approximately planar. Shortening in the C-N (chain) bond distances suggests the presence of a mesomeric effect extended over the entire organic system.     

Transparent Carbon Nanotube Network for Efficient Electrochemiluminescence Devices

A carbon nanotube‐based electrode that combines transparency and good conductivity was used for the first time to develop an electrochemiluminescence (ECL) device. It resulted in an excellent material for ECL applications thanks to the very favorable overpotential of amine oxidation that represents the rate‐determining step for the signal generation in both research systems and commercial instrumentation. The use of carbon nanotubes resulted in a ten times higher emission efficiency compared with commercial transparent indium tin oxide (ITO) electrodes. Moreover, application of this material for proof‐of‐principle ECL imaging was demonstrated, in which micro‐beads were used to mimic a real biological sample in order to prove the possibility of obtaining single cell visualization.     

Analysis of the spatio-temporal scales of laminar premixed flames near equilibrium

The interplay between chemistry and transport is addressed by exploring the coupling between the spatial and temporal scales of one-dimensional laminar premixed combustion in reactive mixtures described by detailed chemical kinetics and multicomponent transport. System dynamics are investigated in the neighbourhood of the equilibrium state; in so doing, the time scales associated with modes of varying wavelength for the complete unsteady, spatially inhomogeneous system are obtained. The results reveal that short wavelength modes are dominated by diffusion-based time scales, and long wavelength modes are dominated by reaction-based time scales. The analysis further identifies critical wavelengths where the effects of reaction and diffusion are balanced, and it is seen that the critical wavelengths are well estimated by classical diffusion theory.     

Synthesis of heteroleptic anthryl-substituted beta-ketoenolates of rhodium(III) and iridium(III): photophysical,electrochemical, and EPR study of the fluorophore-metal interaction

The anthryl-substituted rhodium(III) and iridium(III) heteroleptic beta-ketoenolato derivatives of general formula [M(acac)(2)(anCOacac)] [acac = pentane-2,4-dionate; anCOacac = 3-(9-anthroyl)pentane-2,4-dionate], 3 (M = Rh) and 4 (M = Ir), and [M(acac)(2)(anCH(2)acac)] [anCH(2)acac = 3-(9-anthrylmethyl)pentane-2,4-dionate], 5 (M = Rh) and 6 (M = Ir), were prepared by reacting the corresponding tris(pentane-2,4-dionate)metal complexes, [M(acac)(3)], with 9-anthroyl chloride and 9-chloromethylanthracene, respectively, under Friedel-Crafts conditions. 3-6 were characterized by elemental analysis, ion spray mass spectrometry (IS-MS), (1)H NMR, and UV-vis spectroscopy. The structure of 3 was also elucidated by single-crystal X-ray analysis. When excited at 365 nm, 3-6 result to be poorly luminescent compounds; while the free diketone, i.e., 3-(9-anthrylmethyl)pentane-2,4-dione 1, whose structure was established also by single-crystal X-ray analysis, results to be a strongly light emitting molecule. The study of the electrochemical behavior of 3-6 as well as of the corresponding tris-acetylacetonates of rhodium(III) and iridium(III) allows a satisfactory interpretation of their electrode process mechanism, and gives information about the location of the redox sites along with the thermodynamic and kinetic characterization of the corresponding redox processes. All data are in agreement with the hypothesis that the quenching of the anthracene fluorescence, observed for compounds 3-6, can be due to an intramolecular electron transfer process between the anthryl moiety and the metal-beta-ketoenolato component. Moreover, a study was carried out of the redox behavior of the dyads 3-6 under chemical activation. The one-electron oxidation of compounds 3-6 by thallium(III) trifluoroacetate leads to the formation of the corresponding cation radicals, 3(+)-6(+), whose highly resolved X-band EPR spectra were fully interpreted by computer simulation as well as by semiempirical and DFT calculations of spin density distribution.     

Stereoisomeric sugar-derived indolizines as versatile building blocks: synthesis of enantiopure di- and tetrahydroxyindolizidines.

The synthesis of the sugar-derived (1S,2R,8aR)-1,2-di-O-isopropylidene-1,2,3,5,6,8a-hexahydro-5-oxoindolizine (8) and by analogy of the corresponding stereoisomers ent-8 and ent-7, an epimer at C2 of ent-8, has been accomplished in a straightforward manner. The carbon-carbon double bond and the carbonyl functionalities on the six-membered ring make these nitrogen-containing heterocycles useful building blocks for the efficient preparation of a variety of enantiopure polyhydroxylated indolizidines of interest for their glycosidase inhibitory activity. We report here the synthesis of 2,8a-diepilentiginosine 12 from 8 and the preparation of stereoisomeric 1,2,7,8-tetrahydroxyindolizidines 9-11 performed by OsO4-catalyzed double bond syn dihydroxylation of 7 and 8, followed by deoxygenation of the amide group.     

Electrode surface modification by a spirobifluorene derivative. An XPS and electrochemical investigation

Ordered thin layers of a spirobifluorene derivative containing an amino group were formed by grafting them onto a self-assembled monolayer (SAM) of 11-mercaptoundecanoic acid (11-MUA) on gold. Either physical (H-bonding) or chemical bonding (activated by EDCl) was investigated. X-ray photoelectron spectroscopy and electrochemical impedance spectroscopy confirmed that both methods can be used to effectively graft 2-amino-9,9'-spirobifluorene molecules onto the SAM surface, giving high surface coverages, with a significantly higher packing in the case of chemisorbed films. EIS measurements also showed that the covalently bonded spirobifluorene SAMs act as an effective barrier to both ion penetration and heterogeneous electron transfer.