Chemical Physics Letters (v.550, #C)
Editorial Board (IFC).
Two-dimensional silica: Crystalline and vitreous by M. Heyde; S. Shaikhutdinov; H.-J. Freund (1-7).
Display Omitted► Structural, vibrational, and electronic properties of silica films. ► Monolayer, bilayer and three-dimensional silica structures. ► Atomic resolution of crystalline and a vitreous silica bilayer patches. ► Real space imaging of a crystal to glass transition in the silica bilayer.Two-dimensional SiO2 films may be grown on metal single crystal surfaces. It is possible to grow crystalline and vitreous (glassy) films and study their structural, vibrational, and electronic properties. In particular, the structures of a crystalline and a vitreous film may be imaged with atomic resolution side by side which opens avenues to study long standing problems of real space imaging of a crystal to glass transition.
New investigation on THz spectra of OH and SH radicals (X 2 ∏ i ) by M.A. Martin-Drumel; S. Eliet; O. Pirali; M. Guinet; F. Hindle; G. Mouret; A. Cuisset (8-14).
Display Omitted► Complementarity between broadband synchrotron-based FT-FIR and cw-THz techniques. ► Pure rotational transitions of radicals within their firsts vibrational states. ► Resolution of hyperfine structure of SH radical above 1 THz. ► Resolution of hyperfine structure of OH radical using FT-spectroscopy.Pure rotational transitions of OH and SH radicals have been recorded in the THz spectral range using cw-THz and synchrotron-based FT-FIR techniques. Line lists on these radicals have been completed in the three and two lowest vibrational states for OH and SH, respectively. Furthermore, the hyperfine structure of OH and SH has been observed for the first time using infrared IR FT-spectroscopy, and at frequencies higher than 1 THz, respectively. A combined fit has been made for each of these radicals including v = 0, 1 and 2 for OH and v = 0 and 1 for SH.
Photoelectron spectroscopy and photochemistry of tetracyanoethylene radical anion in the gas phase by Dmitry Khuseynov; Matthew T. Fontana; Andrei Sanov (15-18).
Display Omitted► Adiabatic electron affinity of C2(CN)4 (TCNE) is 3.16 ± 0.02 eV. ► First direct spectroscopic determination of electron affinity of TCNE. ► Photodissociation of TCNE yields CN, C 2 ( CN ) 2 - and C 2 ( CN ) 3 - .A combined photoelectron spectroscopy, photofragmentation and clustering study of the tetracyanoethylene (TCNE) radical anion in the gas phase is reported. The adiabatic electron affinity of TCNE is 3.16(2) eV. This result represents an order-of-magnitude improvement in the uncertainty over the presently accepted, indirectly determined value. The photodissociation of the anion at 355 and 266 nm leads to three anionic channels: one yielding CN− and the other two corresponding to the loss of one or two CN groups from the parent anion. The CN− fragment channel is dominant at 355 nm, while the double-dissociation channel dominates 266 nm photochemistry.
Kinetic simulation of the thermal degradation of phenethyl phenyl ether, a model compound for the β-O-4 linkage in lignin by Ariana Beste; A.C. Buchanan (19-24).
Display Omitted► Pyrolysis of phenethyl phenyl ether, a β-O-4 model compound for lignin. ► Kinetic Monte Carlo based on DFT rate and equilibrium constants. ► α/β-Product selectivity agrees qualitatively with experiment. ► New carbon–carbon phenyl shift reaction identified as part of the mechanism.Employing kinetic Monte Carlo, we simulated the radical chain propagation of the pyrolysis of phenethyl phenyl ether (PPE), which serves as a model compound for the β-O-4 linkage in lignin. The input rate constants were obtained with transition state theory based on density functional calculations. Pre- and postcomplexes for hydrogen abstraction and β-scission reactions were included assuming thermal equilibrium. Individual rate constants compare well with experimental estimates. The calculated overall α/β-product selectivity is qualitatively in agreement with experiment. The simulation revealed that the carbon–carbon phenyl shift reaction for the β-PPE radical is part of the pyrolysis mechanism.
Electron correlation and relativistic effects in atomic structure calculations of Th+, Th2+ ions by S.K. Roy; Rajendra Prasad; Sambhu N. Datta; P. Chandra (25-32).
Display Omitted► In Th+ ion, higher spin–orbit states are strongly affected by core-valence correlation. ► In Th2+ ion, the spin–orbit states are significantly influenced by correlation effect. ► In Th2+ ion, intense transitions are from even to odd parity configurations at correlated level.Relativistic two-component ab initio calculations through second-order Douglas-Kroll-Hess (DKH2) transformation are performed on Th+ and Th2+ ions. Spin–orbit-free calculations are done at SA-CASSCF and MS-CASPT2 levels. Spin–orbit coupled states are studied using effective mean-field operator. Spin–orbit states of Th+, below 23 000 cm−1 are compared with experimental values. Relative separations between various energy levels depend on the amount of electron correlation included in the calculation. For Th2+, spin–orbit energy levels below 20 000 cm−1 agree well with the experimental levels. Transition properties of several spin–orbit states in case of Th2+ ion are predicted.
Silole-based oligomers as electron transport materials by Huyen Thi Nguyen; Vu Thi Thu Huong; Minh Tho Nguyen (33-40).
Display Omitted► Siloles have typical low-lying LUMOs. ► Siloles have reorganization energies comparable to those of thiophenes. ► Silole-based polymers could be promising candidates for electron transport materials.The structure–property relationships of two series of silole-based oligomers including 1,1-substituted oligo(2,5-siloles) and the compounds based on phenylethynylene moieties alternated with fused silole rings (PhEtS) are theoretically investigated using density functional theory. Their electronic, optical and charge transport properties are analyzed in detail. All silole derivatives have typical low-lying LUMOs. The reorganization energies and thereby the charge transport of these oligomers are evaluated. PhEtS molecules show reorganization energies comparable to those of thiophenes that are good for this property. Calculated results thus suggested that silole-based oligomers can be considered as potential candidates to be used as materials for electron transport.
Methane activation on Fe4 cluster: A density functional theory study by Qiao Sun; Zhen Li; Meng Wang; Aijun Du; Sean C. Smith (41-46).
Display Omitted► The study demonstrates Fe4 has strong catalytic effect on the activation reaction of methane. ► The cleavage of the first C–H bond on Fe4 is both an energetically and dynamically favourable process. ► The cluster size of iron can not only determine the activity but also control the product selectivity.We report a comprehensive theoretical study on reaction of methane by Fe4 cluster. This Letter gains insight into the mechanism of the reaction and indicate the Fe4 cluster has strong catalytic effect on the activation reaction of methane. In detail, the results show the cleavage of the first C–H bond is both an energetically and kinetically favourable process and the breaking of the second C–H is the rate-determining step. Moreover, our Letter demonstrates that the different cluster size of iron can not only determine the catalytic activity of methane but also control the product selectivity.
Low energy electron attachment to N-acetylglycine by Janina Kopyra; Constanze König-Lehmann; Eugen Illenberger (47-51).
Display Omitted► Electron attachment to N-acetylglycine occurs preferentially at subexcitation energy (<3 eV). ► Electron capture process is purely dissociative. ► The predominant anion is due to the loss of a hydrogen atom resulting in the formation of (M–H)−.Dissociative electron attachment (DEA) to N-acetylglycine has been studied in the gas phase by means of a crossed beams apparatus. In this Letter we present the results obtained from the target molecule and compare these with the results from its components namely glycine and acetic acid. We find that the number of DEA products is significantly decreased in N-acetylglycine and that the resonance features are notably shifted to lower energies when compared to the individual components. The red shift of the resonances is most likely due to the lower energy of the MOs involved in DEA.
Enhanced Raman spectrum of pyrazine with the aid of resonant electron dynamics in a nearby cluster by Masashi Noda; Tomokazu Yasuike; Katsuyuki Nobusada; Michitoshi Hayashi (52-57).
Display Omitted► Raman spectrum of pyrazine is enhanced with the aid of electron dynamics in Na4. ► Electron dynamics simulation illustrates the details of the mechanism. ► Specific normal modes of pyrazine couple with electronic oscillation in Na4. ► The results show the potential ability of cluster-enhanced Raman scattering.Considerable enhancement of the electric dipole excitation in a pyrazine molecule is computationally demonstrated even under the nonresonant condition with the aid of resonant electron dynamics in a nearby linear Na4 cluster. A real-time and real-space electron dynamics simulation based on time-dependent density functional theory illustrates the details of the enhanced electric dipole excitation through analysis of the time-dependent dipole moment induced in the pyrazine molecule. Specific vibrational normal modes in the molecular plane of pyrazine are found to effectively couple with the photoinduced electronic oscillation of Na4.
Spectroscopic identification of jet-cooled 2,4-dichlorobenzyl radicals generated by corona discharge by Young Wook Yoon; Chang Soon Huh; Sang Kuk Lee (58-61).
Display Omitted► We produce the jet-cooled 2,4-dichlorobenzyl radical by corona discharge. ► We observe the first visible vibronic emission spectra of the 2,4-dichlorobenzyl radical. ► We determine the spectroscopic data on the electronic transition and vibrational modes. ► We explain substituent effect of Cl substitutions on electronic energy of the D1–D0 transition.Vibronically excited but jet-cooled 2,4-dichlorobenzyl radical was generated from the precursor 2,4-dichlorotoluene using a pinhole-type glass nozzle designed for the dual purposes of corona discharge and supersonic jet expansion. From the analysis of the visible vibronic emission spectra of the jet-cooled 2,4-dichlorobenzyl radical observed, substituent effect of two Cl atoms on electronic transition energy was rationalized. In addition, we determined the electronic energy of the D1 → D0 transition and vibrational mode frequencies in the D0 state of the jet-cooled 2,4-dichlorobenzyl radical using the results of an ab initio calculation and known spectroscopic data of the precursor.
High resolution photoabsorption spectrum of hexafluoro-1,3-butadiene (1,3-C4F6) as studied by vacuum ultraviolet (VUV) synchrotron radiation by F. Ferreira da Silva; D. Almeida; E. Vasekova; E. Drage; N.J. Mason; P. Limão-Vieira (62-66).
Display Omitted► High-resolution VUV photoabsorption. ► Electronic excited state. ► Vibronic excitations.In this Letter we present a high resolution VUV photoabsorption spectrum of hexafluoro-1,3-butadiene (1,3-C4F6), over the wavelength range 113–247 nm (11.0–5.0 eV). The spectrum reveals several new features not previously reported in the literature. The assignment of the observed valence and Rydberg transitions and the associated vibronic series is presented based on our recent ab initio calculations on the vertical excitation energies of C4F6 isomers. The dominant excitation has been assigned to the υ1′(a) C＝C stretching mode in the (51A ← 11A, 3pa ← πa(20a)) and (71A ← 11A, 3pb ← πb(19b)) transitions, with mean energies of 0.201 and 0.188 eV, respectively. The measured absolute photoabsorption cross section has been used to calculate the photolysis lifetime of 1,3-C4F6 in the upper stratosphere (20–50 km).
O-Glycosidic bond exocyclic cleavage of difructose led by acidic proton migration: Density functional theory calculation study by Po-Tuan Chen; Tzu-Hsin Chan; Juen–Kai Wang; Yuh-Lin Wang; Michitoshi Hayashi (67-72).
Display Omitted► Glycosidic bond cleavage with water clusters or fructose. ► Energetic and structural details of proton catalytically separating difructose. ► A possible autocatalysis mechanism of difructose assisted by proton. ► The reaction barrier is much lower than directly breaking a covalent bond.We investigate proton migrations from (H2O) n (n = 1–3) to difructose, α-d-fructofuranose-β-d-fructofuranose-2,3′, using density functional theory. The proton migrations result in O-glycosidic bond cleavage. The highest transition barrier for proton migrations taking place from (H2O)3 to difructose is 11.67 kcal mol−1. The barriers are much lower than those for the direct breaking of a covalent bond in a difructose linkage. In addition, an autocatalysis process is also studied. An excess proton can migrate from a fructose molecule to a difructose molecule, leading to O-glycosidic bond cleavage. The transition barrier energy for this proton migration is 5.35 kcal mol−1.
Light-stimulated growth of isotropic domains in nematic liquid crystal by M. Czajkowski; S. Bartkiewicz; J. Mysliwiec (73-78).
Display Omitted► Growth dynamics of photoinduced isotropic domains in azobenzene derivate is studied. ► Theoretical model assuming light stimulation as main reason of the growth is proposed. ► A population of the domains is investigated by diffraction efficiency dynamics. ► Influence of parameters coming from observations is studied by series of simulations. ► Experimental results can be precisely fitted using proposed model.Growth dynamics of single isotropic domains, appearing in liquid crystalline azobenzene derivative during diffraction grating recording has been studied under the polarized microscope. Theoretical approach considering light stimulation as main reason of the growth has been proposed. Growth dynamics of population of the domains has been studied by fitting diffraction efficiency dynamics, using diffraction on rectangular phase grating model. Influence of parameters concerning: material properties, domain growth function and incubation time distribution have been studied by series of simulations. Proposed model explains the local extrema effect on diffraction efficiency curves and can be used for fitting with very good precision.
UV/Vis spectroscopy of C60 embedded in water ice by Steven H. Cuylle; Harold Linnartz; John D. Thrower (79-82).
Display Omitted► Broadband solid state spectroscopy. ► Electronic spectrum of C60@H2O (40 K). ► Solid state signature for frozen C60 in space.Electronic solid state spectra are recorded for C60 embedded in 40 K water ice using broad band direct absorption spectroscopy, and assigned with reference to existing matrix data. The results are interesting in view of the recent gas phase detection of fullerenes in the interstellar medium and provide a realistic solid state signature to search for frozen C60 in space.
Micellar dynamics and water–water hydrogen-bonding from temperature-jump Monte Carlo simulations by G. Heinzelmann; W. Figueiredo; M. Girardi (83-87).
Display Omitted► We obtained three characteristic times for micellization. ► Micellar systems are shown to sacrifice locally the HB network. ► Temperature jump simulations revealed water–surfactant dynamics.We perform Monte Carlo simulations of a model for water–amphiphiles solution to observe the interplay between the formation of micelles and the hydrogen bond (HB) dynamics of the solvent. By performing temperature jumps from a non-micellized to a highly micellized state, we show that the dynamics can be described by three relaxation times. The analysis of HBs reveals an opposite behavior from the water molecules in the first hydration shell of the micelles and their total number indicating that the system is sacrificing HBs locally in order to increase them as a whole.
First principles investigations of the electronic structure and chemical bonding of U3Si2C2 – A uranium silicide–carbide with the rare [SiC] unit by S.F. Matar; R. Pöttgen (88-93).
Display Omitted► For the rare silicide–carbide U3Si2C2, experimental data are best reproduced with GGA + U = 4 eV. ► High linear incompressibility along the c-axis is identified with Si–C alignment leading to anisotropy. ► Chemical bonding is specific of the uranium sites with dominant U1–Si and U2–C. ► Major Si–C bonding contributions characterize the compound.The electronic structure of U3Si2C2, with the rare [SiC] unit is examined from ab initio with an assessment of the properties of chemical bonding. We show that plain GGA fails describing the experimental lattice parameters and the electronic structure. A better agreement with experiment (crystal determination and magnetic properties) is obtained with the GGA + U method and U = 4 eV. The energy–volume equation of state and the set of elastic constants are obtained showing incompressibility along the c-axis with U–C–Si alignment and a brittle material. Bonding of U1 and U2 selectively with Si and C and Si–C bonds are remarkable
Structures and lattice energies of molecular crystals using density functional theory: Assessment of a local atomic potential approach by Zhaoyang Zheng; Jijun Zhao; Yiyang Sun; Shengbai Zhang (94-98).
We have studied the performance of density functional theory plus local atomic potential (DFT + LAP) and with dispersion energy correction for twelve selected molecular crystals including dispersion or/and hydrogen bonding interaction.Display Omitted► The noncovalent interactions between molecular crystals are calculated by DFT + LAP. ► The lattice parameters/energies by DFT + LAP are compared with experimental values. ► The performance of DFT + LAP is compared with DFT-D for noncovalent interactions.Lattice parameters and lattice energies of twelve selected molecular crystals are computed by using density functional theory (DFT) with different treatments of dispersion correction, including the local atomic potential (LAP) and three popular DFT-D methods. Inclusion of LAPs improves the description of intermolecular interactions in molecular crystals over standard DFT calculations. The DFT + LAP approach provides accurate structural parameters and lattice energies that are comparable to the PBE-Grimme scheme. Our results suggest that the DFT + LAP approach is a promising alternative for efficient and accurate quantum simulations on molecular crystals and other systems involving noncovalent interactions.
Molecular dynamics properties of varying amounts of the anticancer drug gemcitabine inside an open-ended single-walled carbon nanotube by Chompoonut Rungnim; Uthumporn Arsawang; Thanyada Rungrotmongkol; Supot Hannongbua (99-103).
Display Omitted► 1–6 Gemcitabine drugs confined inside SWCNT were studied using MD simulation. ► At low content, two adjacent drugs moved together due to π–π stacking formation. ► At high content, the close contact of drugs promotes hydrogen bonding among drugs. ► The drug–drug interaction is an important factor for design of releasing process.To investigate the loading of multiple drugs inside single-walled carbon nanotubes (SWCNTs), molecular dynamics simulations were applied to the gemcitabine–SWCNT system with from one to six drug molecules being confined inside the SWCNT cavity. At low drug concentrations (1–4 gemcitabines inside each SWCNT), the π–π stacking of two cytosine rings of adjacent gemcitabine molecules caused them to orientate towards each other and move together inside the SWCNT. In contrast, at high drug concentrations (encapsulated gemcitabines ⩾5), the close contact of gemcitabines promoted electrostatic interactions through hydrogen bonding rather than the π–π stacking interaction from their cytosine rings.
Gate-voltage-dependent Landau levels in AA-stacked bilayer graphene by Sing-Jyun Tsai; Yu-Huang Chiu; Yen-Hung Ho; Ming-Fa Lin (104-110).
(a) The magnetic-field dependence of the energy gap with (green points) and without (red points) the consideration of the Zeeman effect at V g = 0 . The energy gap as a function of V g at different magnetic fields (b) without and (c) with considering the Zeeman effect.Display Omitted► We study the Landau levels of bilayer graphene in gate voltages by the Peierls tight-binding model. ► The gate voltage strongly influences the Landau level spectra. ► There exist semiconductor–semimetal transitions at certain gate voltages. ► Some carriers are transferred between different layers.The effects of gate voltage V g on the Landau levels (LLs) of the AA-stacked bilayer graphene are investigated by the Peierls tight-binding model. A uniform perpendicular magnetic field ( B 0 ) produces two groups of LLs. V g can raise the threshold LL energies, increase the quantum numbers of the LLs nearest to the chemical potential, and modify the LL spacing. An energy gap is induced by B 0 , and it has an oscillatory dependence on V g and B 0 . There exist semiconductor-semimetal transitions at certain critical gate voltages. Some carriers are transferred between similar sublattices on the two different layers. On the other hand, the main features of the Landau wave functions remain unchanged.
Cooperative behavior in functionalized graphene: Explaining the occurrence of 1,3 cycloaddition of azomethine ylides onto graphene by Pablo A. Denis; Federico Iribarne (111-117).
Display Omitted► Cooperative behavior is responsible for the occurrence of 1,3 dipolar cycloadditions and other organic reactions. ► Reaction energies are increased up to 30 kcal/mol per functional group. ► Functionalization forming infinite armchair lines is the avenue to heavily functionalize graphene. ► The band gap can be varied from 0 to 2 eV!.Cycloaddition reactions onto graphene were studied by means of first-principle calculations. We found that for all reactions studied there is a cooperative behavior responsible for dramatically increasing the reaction energies. This result explains the reason why the 1,3 dipolar cycloaddition of azomethine ylides is both feasible and slow. The cooperative effect decreases in the following order: [2 + 2]-addition of benzynes >1,3-dipolar cycloaddition >[2 + 1]-cycloaddition of NH. This cooperative behavior can open new avenues to fine-tune the physical and chemical properties of graphene. Our results indicate that it is possible to fine tune the band gap of graphene from 0 to 2 eV by varying the number of azomethine groups attached.
Role of lone pair and π-orbital interaction in formation of water nanostructures confined in carbon nanotubes by Arunabhiram Chutia; Ikutaro Hamada; Michio Tokuyama (118-124).
Display Omitted► Confined water in carbon nanotubes. ► ‘Water-chains’, ‘water-cluster’ and ‘water-tube’ like nanostructures. ► Pristine and functionalized carbon nanotubes. ► H-bonding, lone-pair and π-orbital interaction play a major role.A detailed analysis on the geometrical and electronic properties of confined water nanostructures in pristine and functionalized (7, 0) and (10, 0) carbon nanotubes (CNT) is presented. Confined water molecules within these CNTs form similar ‘water-chain’, ‘water-cluster’ and ‘water-tube’ like nanostructures. From the analysis of electronic properties it is clearly evident that the formation of these nanostructures is determined by the interplay between water lone-pair–CNT π orbital interaction and hydrogen bonding between water molecules.
Nanofibrous-like ZnO layers deposited by magnetron sputtering and their integration in dye-sensitized solar cells by O. Lupan; V.M. Guérin; L. Ghimpu; I.M. Tiginyanu; T. Pauporté (125-129).
Very high structural and optical quality ZnO nanofiber layers have been prepared by magnetron sputtering and integrated in dye-sensitized solar cell.Display Omitted► Preparation by magnetron sputtering of ZnO nanofiber network as thick layers. ► High optical and structural quality of the material. ► Good electrical continuity and connection to the substrate. ► High short circuit current dye-sensitized solar cells.We present a cost-effective and fast fabrication of nanofibrous ZnO layers by the magnetron sputtering method. The as-prepared layers were characterized by scanning electron microscopy, energy dispersive X-ray spectrometry, X-ray diffraction, Raman spectroscopy, photoluminescence, and optical studies. The nanofibrous layers show good structural properties offering an excellent nanomaterial for dye-sensitized solar cells (DSSCs) application. Their integration for solar energy conversion is studied by photocurrent–voltage (J–V) measurement, impedance spectroscopy and the developed DSSC structure exhibits promising performances. This Letter provides a technological route to the facile growth of zinc oxide nanofibrous layers through magnetron sputtering, which have several potential applications.
Layer number-dependent structural evolution of two-dimensional diamond films by Hongdong Li; Jia Li; Zhigang Wang; Guangtian Zou (130-133).
Display Omitted► The two dimensional (2D) diamond films were calculated by the first principles calculations. ► The structural evolutions and electrical properties of 2D diamond are dependent on layer number. ► The 2D thinnest diamond film and gradient-graphite-diamond-like structures have been predicted.We report the structural evolution of two-dimensional (1 1 1)-oriented diamond films modulated by the layer number (n) based on first-principles calculations. At n ⩽ 5, the film is relaxed into a few graphene layers; whereas for 6 ⩽ n ⩽ 11, a gradient-graphite-diamond-like (GGDL) structure with gradient changes of interplanar spacing and buckling feature is predicted. A threshold n = 12 is determined to realize the thinnest two-dimensional (1 1 1)-oriented diamond film. The analysis of electronic band structures reveals the transition from semimetal to wide band semiconductor with the increase of n.
Spin orbital effect in lanthanides doped silicon cage clusters by Lingju Guo; Xiaohong Zheng; Z. Zeng; Chao Zhang (134-137).
Display Omitted► Cage-like Si16 clusters can be stabilized by doping Ln atoms. ► Fullerene-like LnSi16 structures are always stable than Frank–Kasper structures. ► Some of the LnSi16 clusters maintain large total magnetic moments. ► The clusters with Pr, Nd, Sm and Tm have large orbital moments. ► The directions of orbital moments and spin moments matches the Hund’s 3rd rule.The stability of lanthanides (Ln) doped silicon cage clusters Ln@Si16 has been proved by theoretical investigations. Particularly, fullerene-like Ln@Si16 structures are always more stable than Frank–Kasper structures, which is different from transition metal doped Si16 clusters. By taking into account the spin–orbital coupling (SOC), some of the Ln@Si16 clusters maintain large total magnetic moments. The clusters with Pr, Nd, Sm and Tm have large orbital moments. We have provided the evidence to clarify the importance of the spin–orbital effect in Ln doped clusters, which may give useful information for further Stern–Gerlach magnetic deflection experiments and theoretical simulations.
Single molecule spectroscopic studies of organic rectifiers composed of pyrene and perylenebisimide by Debra Jo Scardino; Rajesh Kota; Daniell L. Mattern; Nathan I. Hammer (138-145).
Display Omitted► Molecular rectifier properties vary at the single molecule level. ► The presence of pyrene affects perylenebisimide’s fluorescence stability. ► Embedding in polymer thin film stabilizes perylenebisimide’s fluorescence. ► Unique dipole emission patterns reveal molecular orientation in polymer thin film. ► Pyrene acts as a structure directing group for the orientation of perylene within the polymer thin films.Single molecule spectroscopic characteristics of two organic molecular rectifiers are reported. Composed of pyrene as the donor and perylenebisimide (PBI) as the acceptor, these groups are separated by bridges of one or four carbon atoms. Whereas the solution phase absorption and fluorescence spectra are similar, spectra are much more diverse and exhibit different degrees of photostability at the single molecule level. It was found that the addition of pyrene affects the stability of PBI’s emission and analysis of dipole emission patterns reveal that pyrene functions as an orientational directing group for PBI in polymer thin films.
Supersonic quasi-particles dynamics in organic semiconductors by Marcus Vinícius Alves da Silva; Pedro Henrique de Oliveira Neto; Wiliam Ferreira da Cunha; Ricardo Gargano; Geraldo Magela e Silva (146-149).
Display Omitted► Quasi-particles behavior in organic semiconductors is investigated. ► Dynamic study for several external electric fields and impurities. ► Transition from subsonic to supersonic regime was determined. ► Useful information about the conductivity of polymers were obtained.We investigate the dynamics of charge-carriers schemes on high external electric fields in organic semiconductors. Specifically, the critical field strength needed for the transition from subsonic to supersonic regime was determined for solitons and polarons in conjugated polymers, for both trans- and cis-symmetry. Also, the collision between quasi-particles and impurities, at supersonic regime, is investigated. For this purpose it is used a modified Su–Schrieffer–Heeger hamiltonian model in the scope of an Ehrenfest molecular dynamics. The results provide useful information regarding the behavior of the conductivity of conducting polymers measured for different electric fields and bearing different types of impurities.
The cis influence of the corrin in vitamin B12 models by Penny P. Govender; Isabelle Navizet; Christopher B. Perry; Helder M. Marques (150-155).
Display Omitted► DFT calculations explore the cis influence of corrins on Co–CH3 bond homolysis. ► There is normal trans influence between Co–CH3 and Co–NH3 bond lengths. ► Increasing electron donation from the corrin causes the Co–CH3 BDE to decrease. ► Differences in BDE arises from differential stabilization between 6C–Co(III) and 5(C)–Co(II).Density Functional Theory (DFT) and Quantum Theory of Atoms in Molecules (QTAIM) calculations on [NH3[Co(III)(C10-X-corrin)]–CH3]+, where the C10–H of corrin is replaced by electron-donating or –withdrawing groups, X, explore the cis influence in these vitamin B12 models. As the electron donating ability of X increases, a normal trans influence is observed: the Co–NH3 bond weakens while the Co–CH3 bond strengthens. Surprisingly, though, the Co–CH3 bond dissociation energy decreases monotonically as the Co–C bond strengthens. This is found to be a consequence of the extent of shortening of the Co–NH3 during the homolysis reaction.
Phase-cycling schemes for pump–probe beam geometry two-dimensional electronic spectroscopy by Zhengyang Zhang; Kym Lewis Wells; Edward William James Hyland; Howe-Siang Tan (156-161).
Display Omitted► Theoretical explanation and Experimental demonstration of phase cycling schemes for 2D pump probe spectroscopy. ► 1 × 2 Phase cycling recovers both rephasing and nonrephasing 2D spectra under certain experimental situations. ► 1 × 3 Phase cycling recovers all 2D spectra that has been shown hitherto to be only obtained with a 1 × 4 phase cycling scheme. ► Experimental studies performed with excellent agreement with theory.Experimental demonstrations and detailed theoretical explanations are provided for a thorough understanding of the various phase-cycling schemes in an optical pulse shaper assisted two-dimensional electronic spectroscopy (2DES) in a pump–probe beam geometry. We show that two and three-step phase-cycling schemes can be employed to retrieve both rephasing and nonrephasing 2D spectra. The studies were performed on the Qy transition of chlorophyll a.
Short range DFT combined with long-range local RPA within a range-separated hybrid DFT framework by E. Chermak; B. Mussard; J.G. Ángyán; P. Reinhardt (162-169).
Display Omitted► Monomer correlation energies not needed in local orbitals and the dispersion approach. ► Dispersion approximation valid in range-separated DFT even for hydrogen bonded complexes. ► Selection of contributions to the RPA correlation part via mono-excitations useful. ► Singles-CI orbital optimization can be formulated and used advantageously in DFT.Selecting excitations in localized orbitals to calculate long-range correlation contributions to range-separated density-functional theory can reduce the overall computational effort significantly. Beyond simple selection schemes of excited determinants, the dispersion-only approximation, which avoids counterpoise-corrected monomer caculations, is shown to be particularly interesting in this context, which we apply to the random-phase approximation. The approach has been tested on dimers of formamide, water, methane and benzene.
Double effects of high pressure and Sb doping content on thermoelectric properties of Bi2Te3-based alloys by Xin Guo; Xiaopeng Jia; Taichao Su; Kaikai Jie; Hairui Sun; Hongan Ma (170-174).
Display Omitted► We research the thermoelectric properties of Bi2Te3-based with double variables. ► Bi2− x Sb x Te3 is synthesized by a new method of high pressure and high temperature. ► We present an optimal carrier concentration range (3.4 × 1019–3.8 × 1019 cm−3). ► The power factor can be enhanced if carrier concentration is in this range.The purpose of this research is to study the influences of high pressure and Sb doping content on thermoelectric properties of Bi2− x Sb x Te3 alloys. Both variables can adjust the carrier concentration of the system to be more suitable for improving thermoelectric properties. In this Letter, Bi2− x Sb x Te3 is synthesized by high pressure and high temperature (HPHT). The carrier concentration for the excellent power factor of synthesized Bi2− x Sb x Te3 appears in a carrier concentration range. Therefore, we further analyze and present an optimal carrier concentration range, which is favorable for improving thermoelectric properties of Bi2− x Sb x Te3 alloys.
Theoretical and experimental study on narrowing the band gap of carbon nitride photocatalyst by coupling a wide gap molecule by Yong Guo; Juncheng Yang; Sheng Chu; Fei Kong; Leilei Luo; Ying Wang; Zhigang Zou (175-180).
Experimental and theoretical methods have been combined to investigate why PMDA can extend light absorption of wide band gap carbon nitride polymer. Based on VBXPS results and detailed orbital analysis, it is most likely that LUMO of PMDA acts as doping state between CB and VB of wide band gap carbon nitride polymer and extends light absorption by using its LUMO to accept the electron from VB. In addition, the interaction between PMDA and wide band gap carbon nitride polymer influence the energies of CB and VB.Display Omitted► Wide gap anhydride can sensitize wide band gap carbon nitride polymer (CNP). ► Sensitization is realized using LUMO of anhydride to accept electrons of VB in CNP. ► The interaction between anhydride and CNP also influences VB and CB energies of CNP.Experimental and theoretical methods have been combined to investigate why 1,2,4,5-benzene tetracarboxylic dianhydride (PMDA) can extend light absorption of wide band gap carbon nitride polymer. Based on VBXPS results and detailed orbital analysis, it is most likely that LUMO of PMDA acts as doping state between CB and VB of wide band gap carbon nitride polymer and extends light absorption by using its LUMO to accept the electron from VB. In addition, the interaction between PMDA and wide band gap carbon nitride polymer influence the energies of CB and VB.