Chemical Physics Letters (v.630, #C)

Contents (iii-viii).

Novel strong superacids are proposed and investigated on the basis of ab initio calculations. The gas phase acidity of the HAlF4, HAl2F7, and HAl3F10 systems evaluated by the estimation of the Gibbs free energies of their deprotonation reactions were found significant and comparable to the corresponding value characterizing the HTaF6, whereas the strength of the HAl4F13 acid was predicted to exceed that of the HSbF6 acid (the strongest liquid superacid recognized). The deprotonation energies of the HAl n F3n+1 acids (n  = 1–4) turned out to be closely related to the electronic stabilities of their corresponding (Al n F3n+1) anions.

The effects of angular distortions on the H-bond energy are computed in both neutral and ionic complexes. F3CH, NCH, and HNCH+ are taken as CH donors and HCNH, HCNH+, and NH4 + are NH donors. Ionic complexes are more strongly bound and suffer a greater loss of H-bond energy upon angular distortion. However, when bending force constants k are normalized against intrinsic H-bond strength E b , the k/E b ratios are similar, only slightly larger for NH than for CH donors, and with only small perturbations caused by overall charge. The source of destabilization arising from angular deformation is traced to exchange repulsion.

Polymorphism of dioctyl-terthiophene within thin films: The role of the first monolayer by Christoph Lercher; Christian Röthel; Otello Maria Roscioni; Yves Henri Geerts; Quan Shen; Christian Teichert; Roland Fischer; Günther Leising; Michele Sferrazza; Gabin Gbabode; Roland Resel (12-17).
The origins of specific polymorphic phases within thin films are still not well understood. The polymorphism of the molecule dioctyl-terthiophene is investigated during the presence of a silicon-oxide surface during the crystallisation process. It is found that a monolayer of molecules forms two-dimensional crystals on the surface. In the case of thicker films crystalline islands are formed, a comparison of the three polymorphic phases observed within thin films and the thermodynamically more stable single crystal phases reveals distinct differences which can be related to an adaption of the molecular packing with the flat surface of the substrate.

Rotational spectral studies of O(1D) insertion reactions with methane and ethylene: Methanol and vinyl alcohol in a supersonic expansion by Brian M. Hays; Nadine Wehres; Bridget Alligood DePrince; Althea A.M. Roy; Jacob C. Laas; Susanna L. Widicus Weaver (18-26).
Display OmittedWe report a new apparatus for millimeter/submillimeter spectroscopic studies of O(1D) insertion reactions to produce molecules of astrophysical interest. This study focuses on the insertion of O(1D) into methane to form methanol, and the insertion of O(1D) into ethylene to form vinyl alcohol (CH2CHOH). The O(1D) was produced via laser photodissociation of O3 in a fused silica tube and mixed with a hydrocarbon before a supersonic expansion. Direct absorption millimeter/submillimeter spectroscopy was used to monitor the products. The methanol study was used as an experimental benchmark, while the vinyl alcohol study extended rotational spectroscopic measurements to higher frequencies. Observed products from both insertion reactions included, but were not limited to, H2CO, HO2, and CH3O. Methanol and vinyl alcohol were only produced in detectable quantities when the fused silica tube was included, indicating that collisions before the expansion are required for production and stabilization of the O(1D) insertion products.

A conjugated polymer consisting of alternating octyldodecyldiketopyrrolo[3,4-c]pyrrole (DPP) and diethoxynaphthalene (EN) units (PDPP-TENT) with thiophene (T) spacers, was synthesized (M n 19 000), which showed a typical absorption of conjugated polymers (λ max  = 720 nm, solid state). Based on the calculated geometry, PDPP-TENT is only slightly bent (170°) and extensively conjugated. The optical band gap and highest occupied molecular orbital (HOMO) level of the polymer were determined to be 1.61 eV and −5.46 eV, respectively. The polymer-based photovolatic devices (ITO/PED:PSS/PDPP-TENT:PC71BM:diiodooctane/LiF/Al) exhibited the power conversion efficiencies of up to 1.6%.

Two-photon absorption spectra of 4′-hydroxybenzylidene-2,3-dimethylimidazolinone, a model chromophore of enhanced green fluorescent protein (eGFP), were measured in various solvents. The two-photon absorption band of its anionic form is markedly blue-shifted from the corresponding one-photon absorption band in all solvents. Moreover, the magnitude of the blue shift varies largely depending on the solvent, which does not accord with the assignment of the two-photon absorption band to the transitions to the vibrationally excited S1 state. Our finding is readily rationalized by considering overlapping contributions of the S1  ← S0 and S2  ← S0 transitions, suggesting the involvement of the S2 state also in two-photon fluorescence of eGFP.

Diketopyrrolopyrrole-based narrow band gap donors for efficient solution-processed organic solar cells by Sushil S. Bagde; Hanok Park; Seon-nam Yang; Sung-Ho Jin; Soo-Hyoung Lee (37-43).
This study involves the development of two new small molecules comprising a diketopyrrolopyrrole (DPP) core flanked with donor units of triphenylamine (TPA-DPP-TPA) and fluorine (FL-DPP-FL) for application in bulk heterojunction (BHJ) organic solar cells (OSCs). The OSCs based on FL-DPP-FL and PC71BM exhibited a PCE of 1.73%, compared to 1.45% for that obtained from devices of TPA-DPP-TPA. The morphological studies reveal that the enhancement in OSCs of FL-DPP-FL is mainly attributed to the improved nanoscale film morphology of the FL-DPP-FL:PC71BM blend, which promoted the formation of smaller domains and greater donor–acceptor interpenetrated networks within the active layer.

The elastic and mechanical properties of the most stable polymorphs of aspirin and paracetamol are obtained at B3LYP-D2* level of theory to show how effects arising from volumetric expansions related to thermal variations influence the behavior of these materials. Results are in fair agreement with experimental values reported at temperatures far from 0 K, showing that the proposed approach can describe the elastic response of molecular crystals as rationalized in terms of inter-molecular forces. The computational approach, despite its semi-empirical nature, allows achieving a qualitative chemical understanding of the macroscopic mechanical properties of molecular crystals with respect to changes in temperature.

Display OmittedPauling long bond orders have previously been used to obtain qualitative insight in the transmission through nanographenes. Here we show that this long bond order, the atom–atom polarizability (a measure for delocalization) and the transmission probability are intimately linked and that their relationships are valid for all alternant hydrocarbons. These relationships allow a simple rationalization of the transport properties of a variety of molecules considered in molecular electronics. As an example, some molecular wires such as oligo(p-phenylene) are studied, leading to a simple explanation for the experimentally observed exponential decay of the transmission probability with the number of phenyl units.

We have observed fragment-ion images by ultraviolet photodissociation of Mg+ ―FCH3 complex using a reflectron time-of-flight mass spectrometer coupled with an imaging detector. Fourth harmonic of a Nd:YAG laser was used for excitation of Mg+ ―FCH3 from 12A1 to 22A1 state, which has a main character corresponding to Mg+ 2 P  ←  2 S transition. We observed images of MgF+ fragments and determined the kinetic energy release and angular distributions. Among the calculated potential energy curves of Mg+ ―FCH3 along F―C bond length, the 22A1 state was repulsive. The observed energy and angular distributions were consistent with fast MgF+ formation on the repulsive potential energy curve.

The H2S+ ligand was used to study the first proton-transfer (PT1) process in microsolvation and aqueous environments. The average time scale of PT1 of (H2O)3 + clusters (Δt PT1  = 22.8 fs) was notably shorter than that of (H2O)2H2S+ clusters at 79.5 fs. Compared with cationic-water clusters, the smaller potential energy gain observed in the H2S-containing clusters was considered the dominant factor for such slow PT1 dynamics. Δt PT1 of the [H2S]+(aq) at 106.5 fs was significantly longer than the (H2O)2H2S+ clusters. The stabilization effect resulting from the solvent reorientation and formation of H2S+⋯OH2 hemibond interactions was responsible for this delay.

Sampling of biologically important rare events are indispensable for understanding biological functions. As a rare event search method, we have developed TaBoo SeArch algorithm (TBSA), in which states of bio-molecules with low frequency are intensively resampled via short-time molecular dynamics simulations with reference to an inverse histogram projected on a reaction coordinate as a weight in random searches.The one-dimensional inverse histogram is extended herein to a multi-dimensional form as a function of appropriate reaction coordinates. Due to the extension with a restriction on sampled spaces, the protein-folding processes of a chignolin in explicit solvent environment are more efficiently reproduced.

Application of electronic structure methods to coupled Drude oscillators by T.T. Odbadrakh; V. Voora; K.D. Jordan (76-79).
The configuration interaction, perturbation theory, coupled cluster doubles, and random phase approximation methods are applied to a system of two quantum Drude oscillators interacting through dipole–dipole coupling. It is found that the random phase approximation gives the exact excitation energies and exact interaction energy of this system even when allowing only excitations into the first excited levels of the oscillators. In contrast, to obtain the exact results from configuration interaction or coupled cluster treatments of the model requires inclusion of excitations into all accessible excited configurations.

Colloidal silver is used to reduce resistance of reduced graphene oxide (GO). The silver nanoparticles are dispersed on the surface of the GO and intercalated into the layers. The silver doped GO can also form a flexible free standing film with the addition of a polymer. Electrochemical properties of the samples were investigated and find that the pseudo capacitive properties increase in the silver doped samples, resulting in an increase of the capacitance. The resistance of silver doped sample decreases dramatically as well. It, therefore, could be a good candidative electrode for energy storage devices and electrochemical sensors.

Frequency-swept solid-state 33S NMR of an organosulfur compound in an extremely low magnetic field by Kazuhiko Yamada; Daisuke Aoki; Kentaro Kitagawa; Toshikazu Takata (86-90).
Frequency-swept solid-state 33S nuclear magnetic resonance (NMR) spectra of a 33S-enriched organosulfur compound, [33S]-diphenyl disulfide, are presented. The NMR spectra were acquired at extremely low magnetic fields, 0.06 and 0.10 T, which correspond to Larmor frequencies of 0.1959 and 0.3265 MHz, respectively. The quadrupole coupling constant, C Q , and the asymmetry parameter, η Q , for [33S]-diphenyl disulfide were found to be C Q  = 43.3 ± 1.9 MHz and η Q  = 0.70 ± 0.20, respectively. T 1 measurements of [33S]-diphenyl disulfide were performed between 60 and 300 K using nuclear quadrupole resonance signals, and a compromise observation temperature was found to be 300 K. Quantum chemical calculations were performed and the results demonstrated that the quadrupole frequencies and C Q values were highly sensitive to the changes in dihedral angles of disulfide bonds.

Model beryllium-bonded complexes of oxirane and BeX2 (X = H, Cl) were optimized at MP2/6-311++G(d,p). The strength of the O…Be interaction was modified by sequentially replacing the protons of oxirane by F atoms. Systematic variation of the O…Be distance, Be―X bond lengths and stretching frequencies was observed. However, the most interesting trend was for the distortion of the X―Be―X angle, which is strongly dependent on the binding strength – the stronger the beryllium bond, the greater the deviation of this angle from linearity. The charge redistribution due to complexation was also investigated.

Photodissociation and infrared spectra of ethylene cations in solid argon by Sian-Cong Chen; Meng-Chen Liu; Tzu-Ping Huang; Chih-Hao Chin; Yu-Jong Wu (96-100).
We recorded the IR spectra of C2H4 + trapped in solid Ar through electron bombardment of a mixture of ethylene and Ar during matrix deposition. The four most intense lines of C2H4 + were observed and assigned according to comparison with the literature data for ethylene with solid Ne and the predicted vibrational anharmonic wavenumbers. Experiments involving further UV irradiations of the matrix samples were performed in the region 345–225 nm. Upon UV radiation, lines of C2H4 + decreased and lines corresponding to C2H4, C2H2, and C2H3 increased, indicating that the photodissociation and photo-assisted neutralization of C2H4 + in the matrix may occur simultaneously.

Density-functional study of the pure and palladium doped small copper and silver clusters by Hamideh Kahnouji; Halimeh Najafvandzadeh; S. Javad Hashemifar; Mojtaba Alaei; Hadi Akbarzadeh (101-105).
Density functional full potential investigation of pure and Pd mono- and bi-doped small Cu and Ag clusters: structural parameters, magic numbers, GW corrected electronic properties, magnetic moments, and vibrational properties. Display OmittedThe size-dependent properties of small pure copper and silver clusters and their alloys with one and two palladium atoms are studied by using full-potential density functional computations. The stable isomers of these clusters are identified and their magic numbers are determined via the analysis of the second difference of their minimized energy. We discuss that the doped Pd generally prefers the high coordination sites of the pure cluster. It is argued that Pd doping influences the structural cross over of these clusters. The GW correction is applied for more accurate determination of the electronic structure of the systems.

AuO x F y species (x  +  y  = 2–5) are systematically studied using gradient corrected density functional theory. Their vertical detachment energies are larger than the electron affinity of halogen, suggesting them as a new class of superhalogen anions. Attempts have been made to tune the oxidation states of Au successively from +2 to +8 in AuO x F y . However, AuO x F y are stable only up to +5 oxidation state which is predicted to be the highest possible oxidation state of Au. Our calculations clearly show that AuO x F y become unstable and tend to form (AuO x−2F y )O2 complexes when the oxidation state of Au exceeds +5.

Photofragment imaging from mass-selected ions using a reflectron mass spectrometer I. Development of an apparatus and application to Mg+–Ar complex by Hiroshi Hoshino; Yoshihiro Yamakita; Kenichi Okutsu; Yoshitomo Suzuki; Masataka Saito; Kiichirou Koyasu; Keijiro Ohshimo; Fuminori Misaizu (111-115).
The velocity and angular distributions of Mg+(2P3/2) produced by photolysis of Mg+–Ar complex at 4.66 eV were observed using an apparatus set up for imaging fragment ions from mass-selected ions. The translational energy E t and the anisotropy parameter β were measured to be 640 ± 80 cm−1 and 1.03 ± 0.05, respectively. The binding energy of Mg+–Ar in the ground state, estimated to be 1180 ± 80 cm−1, agreed with those reported in the literature. We have demonstrated that the recoil energy as small as 100 meV can be resolved using this apparatus.