Theoretical Investigation on Electronic Transition of Tris(8-quinolinolate) Aluminum Grafted on Poly(p-phenylenevinylene) Units with the Localized-density-matrix Method

An unsystematic molecule PPV‐Alq₃ [3‐(4‐((E)‐2‐(8‐hydroxy‐3‐(4‐styrylstyryl)quinolin‐Alq₂‐6‐yl)vinyl)‐ styryl)‐6‐(4‐styrylstyryl)quinolin‐8‐olate‐Alq₂; q=8‐quinolinolate], which combines poly(p‐phenylenevinylene) with tris(8‐quinolinolate)aluminum, has been studied using a localized‐density‐matrix method. The absorption spectra and electronic transition properties were analyzed and compared with both intermediate neglect of the differential overlap method and the localized‐density‐matrix method. Great efforts have been made on investigating conjugated system on the absorption properties as these can be particularly important for many applications. Two different absorptions of the special molecule, tris(8‐quinolinolate)aluminum grafted on poly(p‐phenylenevinylene) units, were further discussed with density matrices. For the molecule, the first absorption peak is at 413 nm near the purple light. Two 8‐hydroxyquinolines have very slight electronic transition properties. Another absorption peak is at 237 nm. The second characteristic peak of molecule is completely different from that of the first one, which comes from contribution of 8‐hyroxyquinolines in the two different side chains. Our studies show that electronic transition properties of poly(p‐phenylenevinylene) can be effectively tuned by grafting tris(8‐quinolinolate)‐aluminum on poly(p‐phenylenevinylene) from the standpoint of transition energies, frontier molecular orbitals and density matrices.     

MIES and UPS(HeI) studies on reduced TiO2(110)

We have studied reduced TiO₂(110) surfaces by combining metastable impact electron spectroscopy (MIES) and UPS(HeI). The reduced Ti species were preparation‐induced: their number density was modified either by adsorption of K atoms or by a combined annealing/oxygen exposure procedure. The emission from the bandgap state (binding energy 0.9 eV), caused by reduced Ti³⁺ 3d species, was monitored. Bandgap emission is seen clearly with UPS(HeI) and thus can be used to monitor the number density of the near‐surface reduced species. A corresponding spectral structure cannot be seen with MIES. We propose that the excess charge density introduced either by preparation‐induced oxygen vacancies or by K adsorption is delocalized over several surface and subsurface Ti sites; this, together with the partial shielding of the reduced Ti species, prevents detection of the reduced Ti species with MIES. The re‐oxidation and restructuring of the reduced TiO₂(110) surface, caused by simultaneous oxygen exposure and annealing, was studied at temperatures between 400 and 770 K, again by recording the Ti³⁺ 3d emission (0.9 eV bandgap state) with UPS(HeI). The surface can be completely re‐oxidized by oxygen exposure at any selected annealing temperature in the range given above. Morphology changes, leading to a partially reduced surface, take place when the re‐oxidized surface is further annealed at T > 600 K under reducing conditions. The results give support to the assumption that the re‐oxidation is caused by the growth of additional titania whereby the Ti stems from the bulk and the oxygen originates from the gas. The restructuring of the re‐oxidized surface upon annealing under reducing conditions appears to be due to diffusion of Ti interstitials to the surface. Copyright © 2004 John Wiley & Sons, Ltd.     

Single‐crystal neutron‐diffraction study of 3.4% Zn‐doped (ND4)2[Cu(D2O)6](SO4)2 at 20 K

Doping the perdeuterated ammonium copper Tutton salt (ND₄)₂[Cu(D₂O)₆](SO₄)₂ [perdeuterated diammonium hexa­aqua­copper(II) bis­(sulfate)] with Zn leads to a change in the structure from dimorph A (low density) to dimorph B (high density). This change, which accompanies a switch in the direction of the Jahn–Teller distortion, had previously been observed to occur with substitution of Zn²⁺ at the Cu²⁺ site of between 1.3 (A) and 3.4% (B). In this study, the single‐crystal neutron‐diffraction analysis of (ND₄)₂[(Cu/Zn)(D₂O)₆](SO₄)₂ at 20 K, with 3.4% Zn doping and a deuterium substitution of 85% on the H‐atom sites, reveals that the structure is entirely of type B, with the Cu/Zn site at an inversion centre and with no evidence of disorder or unusual atomic displacement parameters that might occur near a phase transition boundary.     

Nature of the near‐IR band in the electronic absorption spectra of neutral bis(tetrapyrrole) rare earth(III) complexes: Time‐dependent density functional theory calculations

The nature of the near‐IR band in the electronic absorption spectra of bis(tetrapyrrole) rare earth(III) complexes Y(Pc)₂ (1), La(Pc)₂ (2), Y(Pc)(Por) (3), Y(Pc)[Pc(α‐OCH₃)₄] (4), Y(Pc)[Pc(α‐OCH₃)₈] (5), and Y(Pc)[Pc(β‐OCH₃)₈] (6) was studied on the basis of time‐dependent density functional theory (TD‐DFT) calculations. The electronic dipole moment along the z‐axis in the electronic transition of the near‐IR band in all the studied neutral bis(tetrapyrrole) yttrium(III) and lanthanum(III) double‐deckers is well explained on the basis of the composition analysis of the orbitals involved. The electronic transition in the near‐IR band causes the reversion of the orbital orientation of one tetrapyrrole ring in both homoleptic and heteroleptic bis(tetrapyrrole) rare earth complexes and induces electron transfer from the tetrapyrrole ring with lower orbital energy to the other ring in the heteroleptic bis(tetrapyrrole) rare earth(III) complexes. The near‐IR band can work as an ideal characteristic absorption band to reflect the π–π interaction between the two tetrapyrrole rings in bis(tetrapyrrole) rare earth(III) double‐decker complexes because of its peculiar electronic transition nature. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010     

Resonance Raman spectra of tris(acetylacetonato)iron(III) and ruthenium(III) complexes and their solvent effect

The resonance Raman spectra of tris(acetylacetonatoiron(III)) and ruthenium(III) complexes in various solvents and in water-acetonitrile (W-AN) mixtures were measured. The resonance Raman spectra of both complexes indicated peaks near 460 and around 1580 cm^–1. Thev(C-O) peak (around 1580 cm^–1) is shifted to low frequency with an increase in the dielectric constant _T of the solvents, whereas thev(M-O) (M=Fe and Ru, near 460 cm^–1) are constant, independent of _T. It implies that the C-O bond in the acac^– ligand is lengthened by the polarizability effect of the solvents, while both the Fe-O and Ru-O bonds, which are located in the inside of the complexes, are not influenced by the solvents indicating that the interaction does not depend on the properties of individual solvent molecules but on those of the aggregate.     

Dielectric study of relaxations and polymorphism in poly(diethyl siloxane)

The dielectric behavior of poly(diethyl siloxane) supports the adiabatic calorimetric findings of Beatty and Karasz. In particular, a sub-T_g transition is observed near ?180°C at 100 Hz, the glass transition near ?135°C at 100 Hz, and a first-order transition near ?70°C (crystal–crystal transformation). This glass-transition temperature is the lowest reported polymeric glass transition for polymers.     

Graphene-Ni (001) interface study

The interfacial properties for a carbon nanotube on a Ni (001) surface are modeled by a piece of vertical graphene standing on a Ni (001) surface. The interaction between the graphene and the nickel (001) surface is investigated using density functional theory (DFT) calculations. Zigzag type graphene can stand on the hollow sites of the Ni (001) surface along the [linear span]110[linear span] direction. For such a configuration, Ni (001)-graphene interfacial mechanical properties are studied, and we find that Ni-Ni bonds near the interface will break first under tensile strain. C-C bond lengths near the interface are longer than the C-C bonds of graphene, and the charge density of those bonds decrease due to the formation of interfacial Ni-C bonds. It suggests that C-C bonds near the interface may break during the carbon nanotube growth processes.     

Janus Face All-cis 1,2,4,5-tetrakis(trifluoromethyl)- and All-cis 1,2,3,4,5,6-hexakis(trifluoromethyl)- Cyclohexanes

We report the synthesis of all-cis 1,2,4,5-tetrakis (trifluoromethyl)- and all-cis 1,2,3,4,5,6-hexakis (trifluoromethyl)- cyclohexanes by direct hydrogenation of precursor tetrakis- or hexakis- (trifluoromethyl)benzenes. The resultant cyclohexanes have a stereochemistry such that all the CF₃ groups are on the same face of the cyclohexyl ring. All-cis 1,2,3,4,5,6-hexakis(trifluoromethyl)cyclohexane is the most sterically demanding of the all-cis hexakis substituted cyclohexanes prepared to date, with a barrier (ΔG) to ring inversion calculated at 27 kcal mol⁻¹. The X-ray structure of all-cis 1,2,3,4,5,6-hexakis(trifluoromethyl)cyclohexane displays a flattened chair conformation and the electrostatic profile of this compound reveals a large diffuse negative density on the fluorine face and a focused positive density on the hydrogen face. The electropositive hydrogen face can co-ordinate chloride (K≈10³) and to a lesser extent fluoride and iodide ions. Dehydrofluorination promoted decomposition occurs with fluoride ion acting as a base.     

A MO-theoretical study of the hydrogen bond in (HCOOH)2, (HCONH2)2 and (B(OH)3)2

The energy decomposition scheme is used with the ab initio MO of the STO-3G minimal basis to elucidate the nature of hydrogen-bondings in (HCOOH)₂, (HCONH₂)₂ and (B(OH)₃)₂. The comparison of the interaction energy and its five components, together with that of the difference density map, reveals the similarity or the difference of these three systems. Each component of the global difference density represents the characteristic role of the corresponding interaction. While the effect of the exchange and charge-transfer interaction is limited to the hydrogen-bonded region, that of the polarization and the coupling terms is spread over the intramolecular bonds of each monomer. The analysis of some orbital interactions is made with respect to (HCOOH)₂ and the importance of the particular charge-transfer interaction is demonstrated.     

Stress-induced crystallization of poly(ethylene terephthalate)

Quenched amorphous films of poly(ethylene terephthalate) (PET) are stretched at temperatures less than T_g; changes in density, wide-angle x-ray diffraction, and small-angle light scattering are observed. The density increase upon stretching is attributed to an increase in crystallinity accompanied by an increase in the intensity of somewhat diffuse wide-angle x-ray diffraction and of both V_V and H_V small-angle light scattering patterns. The formation of oriented rodlike superstructure may be discerned from small-angle light scattering. Annealing of these samples increases the crystallinity as measured from density and leads to an increase in the perfection of crystalline and supercrystalline structure as measured by wide-angle x-ray diffraction and small-angle light scattering. The rodlike morphology changes to form spherulitelike aggregates as observed by small-angle light scattering and light micrographs. A model is proposed to explain the observations. Studies are extended to stretching films of PET above their T_g and observing changes in birefringence, density, wide-angle x-ray diffraction and small-angle light scattering as a function of elongation and stretching temperature. The formation of defomed spherulitelike superstructure may be discèrned from light micrographs. Results are compared with those obtained upon stretching films below T_g.     

Effect of a plant fortifier (Boundary) on pests and predators of greenhouse vegetable crops

Boundary, a plant fortifier composed of extracts of Sophora flavescens Aiton and brown algae, was tested for control of the leaf miner Tuta absoluta (Meyrick) on tomato (three trials) and of the red spider mite Tetranychus urticae Koch on eggplant (one trial) and for side effects on the whitefly predator Macrolophus pygmaeus (Kambur) (two trials) on tomato and on the thrips predators Orius laevigatus (Fieber) and Amblyseius swirskii Athias-Henriot (two trials) on pepper, all in cold greenhouses in South Italy. Control rates for T. absoluta were moderate (40–70%) in the autumn crop but very high and comparable to those for emamectin benzoate in the spring crops (96–100%). Boundary compared well with abamectin against T. urticae, with near complete control. M. pygmaeus was moderately injured in late autumn, but not in early autumn. At the tested application rate and predator population density Boundary was safe for O. laevigatus and A. swirskii.     

Study of structure and spectral characteristics of the binuclear zinc complex with (<Emphasis Type="Italic">E</Emphasis>)-2-({2-[3-(pyridin-2-yl)-1<Emphasis Type="Italic">H</Emphasis>-1,2,4-triazol-5-yl]phenylimino}methyl)phenol

A study of the structure and spectral properties of the compound (E)-2-({2-[3-(pyridin-2-yl)-1H-1,2,4-triazol-5-yl]phenylimino}methyl)phenol and its binuclear complex with zinc was carried out by the quantum-chemical calculations at a level of density functional theory. Within the framework of the time-dependent density functional theory were calculated electron spectra of both compounds, which gave good agreement with experiment, and was revealed the nature of the absorption bands in the visible and near UV region taking into account the solvent effect. Complete interpretation of the absorption bands in the infrared spectra of the complex and protonated ligand was given, and the frequency shift and changes in the intensities of IR bands of the ligand at the complex formation were analyzed.     

Structure and phase transitions in poly(diethylsiloxane)

The structure changes accompanying phase transitions in poly(diethylsiloxane) (PDES) have been studied by WAXS and SAXS techniques using oriented and isotropic samples. PDES may exist in two low-temperature modifications (the monoclinic α₁-form and presumably the “tetragonal” β₁-form) and two high-temperature modifications (the monoclinic α₂-form and the “tetragonal” β₂-form). In linear PDES the crystal - crystal transitions α₁–α₂ and β₁–β₂ occur near 214 and 206 K, respectively. At higher temperatures α₂ (280 K) and β₂ (290 K) forms transform into the mesomorphic phase α_m that gradually melts at 280–300 K giving an amorphous phase. According to x-ray and density data, α_m phase is also characterized by monoclinic structure slightly different from hexagonal packing.     

Mechanism of water photooxidation reaction at atomically flat TiO2 (rutile) (110) and (100) surfaces: dependence on solution pH

The mechanism of water photooxidation reaction at atomically flat n-TiO(2) (rutile) surfaces was investigated in aqueous solutions of various pH values, using photoluminescence (PL) measurements. The PL bands, which peaked at around 810 and 840 nm for the (110) and (100) surfaces, respectively, were assigned to radiative transitions between conduction-band electrons and surface-trapped holes (STH), [Ti-O=Ti(2)](s)+, formed at triply coordinated (normal) O atoms at the surface lattice. The PL intensity (I(PL)) decreased stepwise with increasing solution pH, namely, it sharply decreased at around pH 4, near the point of zero charge of TiO(2) (about 5), and then rapidly decreased to zero near pH 13. The first sharp decrease around pH 4 is attributed to the increased rate of nucleophilic attack of a water molecule to a hole at a site of surface bridging oxygen (Ti-O-Ti), the density of which increases with increasing pH. The nucleophilic attack is regarded as the main initiating step of the water oxidation reaction in low and intermediate pH. The high PL intensity at low pH is ascribed to slow nucleophilic attack owing to a very low density of Ti-O-Ti by its protonation at the low pH. The second sharp decrease near pH 13 is attributed to formation of surface anionic species like Ti-O- which can be readily oxidized by photogenerated holes. Interrelations between reaction intermediates proposed in this work and those reported by time-resolved laser spectroscopy are discussed.     

Asymmetric Cyclizative Dimerization of (ortho-Alkynyl Phenyl) (Methoxymethyl) Sulfides with Palladium(II) Bisoxazoline Catalyst

The first example of an asymmetric cyclization–dimerization of (ortho-alkynyl phenyl) (methoxymethyl) sulfides with a palladium(II) bisoxazoline (box) catalyst has been developed. The box ligand enhances the alkynophilicity of benzothienyl palladium(II) intermediate A and thus promotes coordination of the second alkyne substrate, leading to the dimerization. The characteristic properties of the box ligand were supported by density functional theory (DFT) calculations of the intermediate. Axially chiral bibenzothiophenes were obtained in good yields with good enantioselectivities.     

Intramolecular noncovalent interactions: Bis(toluene)chromium(0) conformers

The structure of trans- and cis-conformers of bis(toluene)chromium(0) and the intramolecular interactions in them are studied by means of MP2 and density functional theory along with topological and NBO analyses. It was concluded for the first time that the locations of two hydrogen atoms of each methyl group between the phenyl ring planes in the most stable cis-conformer of bis(toluene)chromium(0) are largely determined by the stabilizing interactions of methyl C-H bonds and their hydrogen atoms with the metal atom and chromium-carbon bonds. It was concluded from the obtained data that the C-H...Cr contacts in the studied conformers should be considered as hydrogen bonds rather than agostic interactions. Contrary to the existing conception of the quantum theory of atoms in molecules, repulsive interaction is shown to occur between the pairs of hydrogen atoms of the two methyl groups in bis(toluene)chromium(0) cis-conformers rather than the stabilizing hydrogen-hydrogen interactions.     

Volatiles of Helichrysum italicum (Roth) G. Don from Croatia

Helichrysum italicum (Roth) G. Don is a flowering plant of the family Asteraceae. It is rich in oil that is used for different medicinal purposes and in fragrance industry. Volatile profile of four populations of H. italicum, collected from natural habitat in Dalmatia (Croatia), was analysed by capillary GC–MS. Sample from Bra? Island had α-trans-bergamotene (10.2%) and β-acoradiene (10.1%) as the majors, whereas sample collected on Biokovo Mt. was rich in neryl acetate (8.1%). β-Acoradiene was also the main constituent of sample collected near Tijarica, whereas rosifoliol (8.5%) was the most abundant constituent in sample collected near Makarska. Presented results show the influence of environmental conditions on chemical differentiation of the volatiles of H. italicum from Croatia.     

Miscibility of poly(styrene‐co‐butyl acrylate) with poly(ethyl methacrylate): Existence of both UCST and LCST

A miscible homopolymer–copolymer pair viz., poly(ethyl methacrylate) (PEMA)–poly(styrene‐co‐butyl acrylate) (SBA) is reported. The miscibility has been studied using differential scanning calorimetry. While 1 : 1 (w/w) blends with SBA containing 23 and 34 wt % styrene (ST) become miscible only above 225 and 185 °C respectively indicating existence of UCST, those with SBA containing 63 wt % ST is miscible at the lowest mixing temperature (i.e., T_g's) but become immiscible when heated at ca 250 °C indicating the existence of LCST. Miscibility for blends with SBA of still higher ST content could not be determined by this method because of the closeness of the T_g's of the components. The miscibility window at 230 °C refers to the two copolymer compositions of which one with the lower ST content is near the UCST, while the other with the higher ST content is near the LCST. Using these compositions and the mean field theory binary interaction parameters between the monomer residues have been calculated. The values are χ_ST‐BA = 0.087 and χ_EMA‐BA = 0.013 at 230 °C. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 369–375, 2000     

Poly(aryl ether amide)s

A general method for the preparation of poly(aryl ether amide)s has been developed where the generation of an aryl ether linkage is the polymer-forming reaction. The amide linkage was found to be sufficiently electron-withdrawing to activate halo-substituents towards nucleophilic aromatic substitution analogous to conventional activating groups (i.e., sulfone, ketone, etc.). Model reactions demonstrated that the amide-activated displacement occurred with high selectivity in near quantitative yield and was judged suitable as a polymer-forming reaction. Appropriately fluoro-substituted amides were prepared and subjected to displacement polymerization with bisphenoxides in a N-methyl-2-pyrrolidone (NMP)/N-cyclohexyl-2-pyrrolidone (CHP) solvent mixture. High molecular weight polymers with glass transition temperatures in the 200–225°C range were obtained. © 1993 John Wiley & Sons, Inc.     

The two-dimensional band structure of (polyphthalocyaninato)Ni(II)

The two-dimensional (2D) band structure of (polyphthalocyaninato)Ni(II), Ni(ppc), has been analyzed by a self-consistent field (SCF ) Hartree–Fock (HF ) crystal orbital (CO ) formalism based on an INDO (intermediate neglect of differential overlap) type Hamiltonian. The calculated HF band gap of Ni(ppc) amounts to 0.24 eV. The highest filled band is a ringlike a_1u combination (D_4h symmetry label) localized at the carbon sites of the organic fragment. Remarkable hybridization in the valence band leads to the considerable band width Δ?_v of 2.92 eV. This value is close to the Δ?_v numbers which are conventionally encountered in one-dimensional metallomacrocycles. The effective width of the states in Ni(ppc) is 13.8 eV. In graphite a net π interval of 13.0 eV is predicted by the present CO formalism; i.e., the energetic distribution of the π electrons is roughly comparable in both 2D solids. The Ni 3d states in Ni(ppc) are far below the Fermi level which is calculated at ?4.9 eV; they are predicted between ?12.2 and ?16.4 eV in the mean-field approximation. Quasi-particle corrections lead to a significant shift of these strongly metal-centered states. Important electronic structure properties of Ni(ppc) are compared with those of 1D metallomacrocycles with similar molecular stoichiometry. The total density of states distribution of Ni(ppc) has been fragmented into projected (ligand π and σ, Ni 3d) contributions in order to allow for a transparent interpretation of the 2D band structure.