The Chiral 1:2 Adduct (S)S(S)C(-)589-Ethyl 2-Phenylbutyl Sulphide-Mercury (II) Chloride:(-)589[(S)S(S)C-Et(2-PhBu)S.(HgCl2)2]. Stereoselective Synthesis, Asymmetric Oxidation, Crystal and Molecular Structure and Circular Dichroism Spectra.

Optically active (-)589ethyl (S)-2-phenylbutyl thioether, (-)(S)C-Et(PhBu)S (I), and its new diastereoisomeric mercury (II) chloride adduct, 1:2, (-)[(S)S(S)C-Et(PhBu)S.(HgCl2)2]2, (II) were stereoselectively synthesized; the absorbance (UV) and circular dichroism (CD) spectra were measured and the crystal and molecular structure of complex (II) was determined by single-crystal X-ray diffraction. Two different Hg centres are present whose coordination environments are built by two short bonds to chloride ligands in one case, and to one chloride and one sulphur in the other one. These originate digonal units. Electroneutrality is achieved by a further chlorine, which can be considered prevalently ionic and bonded to the two Hg centres, forming square bridging systems nearly perpendicular to the digonal molecules. The coordination polyhedra can be interpreted as 2 + 4 tetragonally-compressed octahedra with the four longer contacts lying in the equatorial plane. IR spectroscopic data are consistent with the presence of one bent and one linear Cl-Hg-Cl moiety. The absolute configurations at both stereogenic centres of the formed diastereoisomeric complex (II) are (S). The (S)S absolute configuration at the stereogenic sulphur atom bonded to the mercury(II) atom in complex (II) has been related with the negative Cotton effect assigned in its circular dichroism (CD) spectrum to a charge-transfer transition at ca. 230 nm. The stereoselective oxidation of (I) and (II) with hydrogen peroxide, induced by the stereogenic carbon atom (S)C of the enantiopure sulphide, gave (-)598ethyl (S)C-2-phenylbutyl(S)S-sulphoxide, (-)598[(S)S(S)C-Et(PhBu)SO], (III), having 18.1% de. Oxidations carried out in the presence of a 200 molar excess of mercury(II) chloride gave (-)598ethyl (S)C-2-phenylbutyl(R)S-sulphoxide, (-) 598[(R)S(S)C-Et(PhBu)SO], (IV) with 31% de, showing the cooperative influence of mercury(II) chloride on the selectivity of the oxidation reaction.

Epitaxial growth of π-stacked perfluoropentacene on graphene-coated quartz.

Chemical-vapor-deposited large-area graphene is employed as the coating of transparent substrates for the growth of the prototypical organic n-type semiconductor perfluoropentacene (PFP). The graphene coating is found to cause face-on growth of PFP in a yet unknown substrate-mediated polymorph, which is solved by combining grazing-incidence X-ray diffraction with theoretical structure modeling. In contrast to the otherwise common herringbone arrangement of PFP in single crystals and "standing" films, we report a π-stacked arrangement of coplanar molecules in "flat-lying" films, which exhibit an exceedingly low π-stacking distance of only 3.07 Å, giving rise to significant electronic band dispersion along the π-stacking direction, as evidenced by ultraviolet photoelectron spectroscopy. Our study underlines the high potential of graphene for use as a transparent electrode in (opto-)electronic applications, where optimized vertical transport through flat-lying conjugated organic molecules is desired.

Crystal-to-crystal photoinduced reaction of dinitroanthracene to anthraquinone.

The photochemical reaction of 9,10-dinitroanthracene (DNO(2)A) to anthraquinone (AQ) + 2NO has been studied by means of lattice phonon Raman spectroscopy in the spectral region 10-150 cm(-1). In fact, crystal-to-crystal transformations are best revealed by following changes in the lattice modes, as even small modifications in the crystal structure lead to dramatic changes in symmetry and selection rules of vibrational modes. While analysis of the lattice modes allowed for the study of the physical changes, the chemical transformation was monitored by measuring the intramolecular Raman-active modes of both reactant and product. On the basis of the experimental data it has been possible, at a microscopic level, to infer crucial information on the reaction mechanism by simultaneously detecting molecular (vibrational modes) and crystal structure (lattice phonons) modifications during the reaction. At a macroscopic level we have detected an intriguing relationship between incident photons and mechanical strain, which manifests itself as a striking bending and unfolding of the specimens under irradiation. To clarify the mechanisms underlying the relationship between incoming light and molecular environment, we have extended the study to high pressure up to 2 GPa. It has been found that above 1 GPa the photoreaction becomes inhibited. The solid-state transformation has also been theoretically modeled, thus identifying the reaction pathway along which the DNO(2)A crystal lattice deforms to finally become the crystal lattice of the AQ product.

Phonon dynamics and electron-phonon coupling in pristine picene.

The paper reports a complete analysis of the phonon structure of crystalline picene, a recently announced organic semiconductor. Both lattice and intramolecular vibrations are investigated. An exhaustive assignment of lattice phonons is obtained through polarized Raman spectra assisted by lattice dynamics calculations based on a well tested atom-atom potential model. Raman, infrared spectra and density functional (DFT) calculations are used for the characterization of intramolecular modes. Coupling between low-frequency molecular vibrations and lattice phonons is accounted for. Molecule-to-molecule transfer integrals, as well as the Peierls and Holstein (non-local and local) coupling constants, are evaluated through the semiempirical method INDO/S (Intermediate Neglect of Differential Overlap with Spectroscopic parametrization).

High-performance single crystal organic field-effect transistors based on two dithiophene-tetrathiafulvalene (DT-TTF) polymorphs.

Solution prepared single crystal organic field-effect transistors (OFETs) combine low-cost with high performance due to structural ordering of molecules. However, in organic crystals polymorphism is a known phenomenon, which can have a crucial influence on charge transport. Here, the performance of solution-prepared single crystal OFETs based on two different polymorphs of dithiophene-tetrathiafulvalene, which were investigated by confocal Raman spectroscopy and X-ray diffraction, are reported. OFET devices prepared using different configurations show that both polymorphs exhibited excellent device performance, although the -phase revealed charge carrier mobility between two and ten times higher in accordance to the closer stacking of the molecules.

Polymorphism and phonon dynamics of alpha-quaterthiophene.

Low-frequency (10-150 cm(-1)) Raman spectra of the low-temperature (LT) and high-temperature (HT) polymorphs of the organic semiconductor alpha-quaterthiophene at 300 and 10 K are reported. Polarized spectra, assisted by quasi-harmonic lattice dynamics (QHLD) calculations, allow characterization of the lattice phonon dynamics and identification of the two phases spectroscopically. The experimental data can be explained by taking into account the coupling between intermolecular (lattice) and low-frequency intramolecular modes. Finally, Raman mapping is used to investigate the phase purity.

Field effect transistors with organic semiconductor layers assembled from aqueous colloidal nanocomposites.

We demonstrate field effect transistors based on organic semiconductor molecules dispersed in a self-organized polystyrene (PS) latex bead matrix. An aqueous colloidal composite made of PS and tetrahexylsexithiophene (H4T6) is deposited with a micropipet into the channel of a bottom-contact field effect transistor. The beads self-organize into a network whose characteristic distances are governed by their packing. The semiconductor molecules crystallize in the interstitial voids, leading to the growth of large interconnected domains. Depending on the bead size and the ratio between H4T6 and PS, the fraction of the different phases in the polymorph can be controlled. In the transistors where the H4T6 metastable "red phase" is the largest, the device response and the charge mobility are comparable to those of sexithienyl thin films grown by high-vacuum sublimation.

Reflectance circular dichroism of solid-state chiral coordination compounds.

Solid-state diffuse reflectance circular dichroism (DRCD) spectra of some chiral lambda- and delta-M[(A--A)(n)](m+) coordination compounds [M(III) = Cr, Co; A--A = ethylendiamine (en), O,O'-2(R)3(R)dimethylethylene dithiophosphate ion, (R,R)bdtp(-), sepulchrate (Sep); n = 1, 3; m = 0, 3] were measured and compared with their solution, nujol mull, and KBr pellet spectra in the spectral region of 300-800 nm. The validity of the DRCD method to obtain reliable CD spectra which reflect a correct absolute configuration at the metal coordination center as well as subtle changes in the stereochemistry of the compound in the solid vs. solution states was proved. DRCD is the only spectroscopic method to examine randomly oriented chiral compounds without the effect of pressure, solvent, or diluting media such as KBr or nujol (which lends the sample irrecoverable and may interact with the sample), and directly relate to the structure that is revealed by X-ray diffractometry.