Kosterlitz-Thouless-type transition in a charge ordered state of the layered organic conductor α-(BEDT-TTF)2I3.

The current-voltage characteristics in the charge order state of the two-dimensional organic conductor α-(BEDT-TTF)(2)I(3) exhibit power law behavior at low temperatures. The power law is understood in terms of the electric-field-dependent potential between electrons and holes, which are thermally excited from the charge order state. The power law exponent steeply changes from 1 to 3 in the range from 30 to 45 K with decreasing temperature, thereby suggesting the occurrence of a Kosterlitz-Thouless-type transition; many (few) unbound electron-hole pairs are thermally excited above (below) the transition. The effects of the finite size and interlayer coupling on the power law behavior are discussed.

Early-stage dynamics of light-matter interaction leading to the insulator-to-metal transition in a charge ordered organic crystal.

Ultrafast dynamics of the light-matter interaction in a charge-ordered molecular insulator α-(BEDT-TTF)2I3 were studied by pump-probe spectroscopy using few-optical-cycle infrared pulses (pulse width 12 fs). Coherent oscillation of the correlated electrons and subsequent Fano destructive interference with intramolecular vibration were observed in time domain; the results indicated a crucial role for electron-electron interplay in the light-matter interaction leading to the photoinduced insulator-to-metal transition. The qualitative features of this correlated electron motion were reproduced by calculations based on exact many-electron-phonon wave functions.

Photoinduced melting of a stripe-type charge-order and metallic domain formation in a layered BEDT-TTF-based organic salt.

Photoinduced melting of charge-order (CO) in [bis(ethylenedithiolo)]-tetrathiafulvalene (BEDT-TTF) salts was investigated by femotosecond spectroscopy. Comparative studies on two polytypes exhibiting large [theta-(BEDT-TTF)2RbZn(SCN)_{4}] and small [alpha-(BEDT-TTF)2I3] molecular rearrangements through the CO transition were performed. Ultrafast melting of CO for both compounds demonstrates the major contribution of the electronic instability which is due to Coulomb interaction. The roles of the molecular rearrangements on the formation of the CO and the metallic domain are discussed on the basis of low-frequency lattice dynamics.

Assignment of the in-plane molecular vibrations of the electron-donor molecule BDT-TTP based on polarized Raman and infrared spectra, in which BDT-TTP is 2,5-bis(1,3-dithiol-2-ylidene)-1,3,4,6-tetrathiapentalene.

Infrared and Raman spectra of 2,5-bis(1,3-dithiol-2-ylidene)-1,3,4,6-tetrathiapentalene (BDT-TTP) and 1,3,4,6-tetrathiapentalene-2,5-dione (TTP-DO) are reported. The vibrational modes of TTP-DO are assigned with the aid of the depolarization ratio of solution Raman spectra, polarized reflection spectra and polarized Raman spectra. A D2h symmetry is assumed for the BDT-TTP molecule and its in-plane fundamental vibrations are assigned with the aid of the polarization ratio and the correlation with TTP-DO, tetrathiafulvalene (TTF), tetramethyltetrathiafulvalene (TMTTF) and bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF). Normal coordinate calculation with a modified internal valence force field was carried out for the in-plane fundamental vibrations of TTP-DO and BDT-TTP. Ab initio calculations of the normal modes of BDT-TTP0 and BDT-TTP+ are compared with the empirical analysis.

Crystal chemistry and physical properties of superconducting and semiconducting charge transfer salts of the type (BEDT-TTF)(4)[A(I)M(III)(C2O4)3]*PhCN (A(I) = H30,NH4,K; M(III) = Cr, Fe, Co, Al; BEDT-TTF = bis(ethylenedithio)tetrathiafulvalene.

Synthesis, structure determination by single-crystal X-ray diffraction, and physical properties are reported and compared for superconducting and semiconducting molecular charge-transfer salts with stoichiometry (BEDT-TTF)(4)[A(I)M(III)(C(2)O(4))(3)].PhCN, where A(I) = H(3)O, NH(4), K; M(III) = Cr, Fe, Co, Al; BEDT-TTF = bis(ethylenedithio) tetrathiafulvalene. Attempts to substitute M(III) with Ti, Ru, Rh, or Gd are also described. New compounds with M = Co and Al are prepared and detailed structural comparisons are made across the whole series. Compounds with A = H(3)O(+) and M = Cr, Fe are monoclinic (space group C2/c), at 150, 120 K a = 10.240(1) A, 10.232(12) A; b = 19.965(1) A, 20.04(3) A; c = 34.905(1) A, 34.97(2) A; beta = 93.69(1) degrees, 93.25(11) degrees, respectively, both with Z = 4. These salts are metallic at room temperature, becoming superconducting at 5.5(5) or 8.5(5) K, respectively. A polymorph with A = H(3)O(+) and M = Cr is orthorhombic (Pbcn) with a = 10.371(2) A, b = 19.518(3) A, c = 35.646(3) A, and Z = 4 at 150 K. When A = NH(4)(+), M = Fe, Co, Al, the compounds are also orthorhombic (Pbcn), with a = 10.370(5) A, 10.340(1) A, 10.318(7) A; b = 19.588(12) A, 19.502(1) A, 19.460(4) A; c = 35.790(8) A, 35.768(1) A, 35.808(8) A at 150 K, respectively, with Z = 4. All of the Pbcn phases are semiconducting with activation energies between 0.15 and 0.22 eV. For those compounds which are thought to contain H(3)O(+), Raman spectroscopy or C=C and C-S bond lengths of the BEDT-TTF molecules confirm the presence of H(3)O(+) rather than H(2)O. In the monoclinic compounds the BEDT-TTF molecules adopt a beta' ' packing motif while in the orthorhombic phases (BEDT-TTF)(2) dimers are surrounded by monomers. Raman spectra and bond length analysis for the latter confirm that each molecule of the dimer has a charge of +1 while the remaining donors are neutral. All of the compounds contain approximately hexagonal honeycomb layers of [AM(C(2)O(4))(3)] and PhCN, with the solvent occupying a cavity bounded by [M(C(2)O(4))(3)](3-) and A. In the monoclinic series each layer contains one enantiomeric conformation of the chiral [M(C(2)O(4))(3)](3-) anions with alternate layers having opposite chirality, whereas in the orthorhombic series the enantiomers form chains within each layer. Analysis of the supramolecular organization at the interface between the cation and anion layers shows that this difference is responsible for the two different BEDT-TTF packing motifs, as a consequence of weak H-bonding interactions between the terminal ethylene groups in the donor and the [M(C(2)O(4))(3)](3-) oxygen atoms.

Activation of N-nitrosodialkylamines by near-ultraviolet irradiation: formation of directly-acting mutagens and DNA-damaging products.

On near-ultraviolet (UVA) irradiation in a phosphate buffer, N-nitrosomorpholine (NMOR) and N-nitrosopyrrolidine (NPYR) were converted into directly-acting mutagens. The activated NPYR was fractionated, and the active product was isolated. The compound was shown to be identical to alpha-phosphonooxy NPYR on the basis of several properties: retention times in high-performance liquid chromatograms, mutagenic specificity and potency, ultraviolet spectrum, and inactivation by phosphatase treatment. Photoactivation was inhibited by superoxide dismutase, and therefore superoxide is implicated as playing a key role in mutagen formation. N-Nitrosoproline (NPRO) and eighteen other N-nitrosodialkylamines were irradiated with UVA in the presence of phi X174 RFI DNA. The DNA underwent single-strand breaks to give RFII DNA, indicating that N-nitrosodialkylamines in general have this property. DNA chain cleavage was inhibited both by superoxide dismutase and hydroxyl-radical scavengers. These results provide new information on the genotoxic mechanism of action of N-nitrosodialkylamines.