Reversible Light‐Driven Polymerization of Polyoxometalate Tethered with Coumarin Molecules

A new photosensitive polyoxometalate (POM) organic–inorganic hybrid compound has been prepared by covalently tethering coumarin moieties onto a Mn–Anderson cluster. This compound has been fully characterized by ¹H NMR, ¹³C NMR, FTIR, and UV/Vis spectroscopy, and ESI‐MS. This organic–inorganic hybrid compound can undergo reversible light‐driven polymerization and this process has been characterized in detail.     

Isolation of extendable transition metal incorporated polyoxometalate intermediates with structural control

Three discrete cobalt-substituted silicotungstates, [Co3(H2O)(B-beta-SiW9O34)(B-beta-SiW8O29(OH)2)]12- (1), [Co3(H2O)(B-alpha-SiW9O34)(B-beta-SiW8O31)]14- (2), and [Co9Cl2(OH)3(H2O)9(B-beta-SiW8O31)3]17- (3), have been synthesized using a synthetic approach involving Co(II) ions, the dilacunary [gamma-SiW10O36]8- polyanion and a bulky organic cation in basic media; all three compounds have been fully characterized and their position as structural intermediates in Co-containing silicotungstate chemistry is described.     

Thermally controlled preferential molecular aggregation state in a thiacarbocyanine dye

Herein we report the experimental and theoretical study of the temperature dependence of a thiacarbocyanine dye in its monomer, H- and J-aggregates states. We demonstrate the ability to control the ratio of monomer, H- and/or J-aggregates with heat. We link such a control to the conformation dependence of the molecule. An alternative way to gain access to the dominating species without changing the concentration as a complete switching mechanism between all the present species is proposed. The results presented in this work lead to a better understanding of thiacarbocyanine dye's behavior.     

Sensitization of lanthanoid luminescence by organic and inorganic ligands in lanthanoid-organic-polyoxometalates

The reaction of terbium and europium salts with the lacunary polyxometalate (POM) [As(2)W(19)O(67)(H(2)O)](14-) and 2-picolinic acid (picH) affords the ternary lanthanoid-organic-polyoxometalate (Ln-org-POM) complexes [Tb(2)(pic)(H(2)O)(2)(B-β-AsW(8)O(30))(2)(WO(2)(pic))(3)](10-) (1), [Tb(8)(pic)(6)(H(2)O)(22)(B-β-AsW(8)O(30))(4)(WO(2)(pic))(6)](12-) (2), and [Eu(8)(pic)(6)(H(2)O)(22)(B-β-AsW(8)O(30))(4)(WO(2)(pic))(6)](12-) (3). A detailed synthetic investigation has established the conditions required to isolate pure bulk samples of the three complexes as the mixed salts H(0.5)K(8.5)Na[1]·30H(2)O, K(4)Li(4)H(4)[2]·58H(2)O, and Eu(1.66)K(7)[3]·54H(2)O, each of which has been characterized by single crystal X-ray diffraction. Complexes 2 and 3 are isostructural and can be considered to be composed of two molecules of 1 linked through an inversion center with four additional picolinate-chelated lanthanoid centers. When irradiated with a laboratory UV lamp at room temperature, compounds K(4)Li(4)H(4)[2]·58H(2)O and Eu(1.66)K(7)[3]·54H(2)O visibly luminesce green and red, respectively, while compound H(0.5)K(8.5)Na[1]·30H(2)O is not luminescent. A variable temperature photophysical investigation of the three compounds has revealed that both the organic picolinate ligands and the inorganic POM ligands sensitize the lanthanoid(III) luminescence, following excitation with UV light. However, considerably different temperature dependencies are observed for Tb(III) versus Eu(III) through the two distinct sensitization pathways.     

Electronic polarization effects in the photodissociation of Cl2

Velocity mapped ion imaging and resonantly enhanced multiphoton ionization time-of-flight methods have been used to investigate the photodissociation dynamics of the diatomic molecule Cl(2) following excitation to the first UV absorption band. The experimental results presented here are compared with high level time dependent wavepacket calculations performed on a set of ab initio potential energy curves [D. B. Kokh, A. B. Alekseyev, and R. J. Buenker, J. Chem. Phys. 120, 11549 (2004)]. The theoretical calculations provide the first determination of all dynamical information regarding the dissociation of a system of this complexity, including angular momentum polarization. Both low rank K = 1, 2 and high rank K = 3 electronic polarization are predicted to be important for dissociation into both asymptotic product channels and, in general, good agreement is found between the recent theory and the measurements made here, which include the first experimental determination of high rank K = 3 orientation.     

Toxicity of chemical mixtures: proteomic analysis of persisting liver and kidney protein alterations induced by repeated exposure of rats to JP-8 jet fuel vapor

Male Sprague-Dawley rats were exposed by whole body inhalation to 1000 mg/m3 +/- 10% JP-8 jet fuel vapor or room air control conditions for 6 h/day, 5 days/week for six consecutive weeks. Following a rest period of 82 days rats were sacrificed, and liver and kidney tissues examined by proteomic methods for both total protein abundance and protein charge modification. Kidney and lung samples were solubilized and separated via large scale, high resolution two-dimensional electrophoresis (2-DE) and gel patterns scanned, digitized and processed for statistical analysis. Through the use of peptide mass fingerprinting, confirmed by sequence tag analysis, three altered proteins were identified and quantified. Numerical, but not significantly different increases were found in total abundance of lamin A (NCBI Accession No. 1346413) in the liver, and of 10-formyltetrahydrofolate dehydrogenase (10-FTHF DH, #1346044) and glutathione-S-transferase (GST; #2393724) in the kidneys of vapor-exposed subjects. Protein charge modification index (CMI) analysis indicated significant alterations (P < 0.001) in expressed lamin A and 10-FTHF DH. These persisting changes in liver and kidney proteins are discussed in terms of possible alterations in the functional capacity of exposed subjects.     

Photon equation of motion with application to the electron’s anomalous magnetic moment

The photon equation of motion previously applied to the Lamb shift is here applied to the anomalous magnetic moment of the electron. Exact agreement is obtained with the QED result of Schwinger. The photon theory treats the radiative correction to the photon in the presence of the electron rather than its inverse as in standard QED. The result is found to be first order in the photon-electron interaction rather than second order as in standard QED, introducing an ease of calculation hitherto unavailable.     

Chirped quantum cascade laser induced rapid passage signatures in an optically thick gas

We report observations of rapid passage signals induced in samples of N₂O and CH₄ present in a multipass cell with an optical path length of 5 m. The effect of laser power and chirp rate upon the signals has been studied by utilising two different chirped quantum cascade lasers operating around 8 μm. The rapid passage signals exhibit an increasing delay in the switch from absorption to emission as a function of increased gas pressure (up to 8 Torr of gas). By comparing a selection of transitions in N₂O and CH₄, we show that, unlike ammonia, this ‘pressure shift’ is independent of the transition dipole moment, spectroscopic branch probed and laser chirp rate. As the transition dipole moment is much larger in nitrous oxide than methane, we believe that this indicates that N₂O–N₂O collisions are more efficient at removing coherence from the polarised sample than CH₄–CH₄ collisions. We have also observed this pressure shift in a short path length of 40 cm, although with a much reduced value, indicating that propagation effects are important in this optically thick minimally damped system.     

Single-photon detection mechanism in a quantum dot transistor

We study the transport mechanisms in a quantum dot MODFET by tuning the localization induced by charge stored on the quantum dots with light. The temperature dependence of the resistivity of a macroscopic sample reveals a hopping transport when the dots contain an excess of electrons. The resistance of a mesoscopic sample however, which is capable of detecting single photons, exhibits a much weaker dependence upon temperature. This points towards source-drain tunnelling as a transport mechanism and is confirmed by a statistical analysis of the single-photon-induced conductance steps. The complexity of the conducting paths increases as the average hopping length reduces.