Growth Mechanisms of Fluorescent Silver Clusters Regulated by Polymorphic DNA Templates: A DFT Study

Interactions between fullerene C24 and a frequently used supplement for sport activities, ephedrine (EPH), have been studied in detail by a combination of density functional theory (DFT), time dependent DFT (TD-DFT) calculations, the symmetry-adapted perturbation theory (SAPT) approach and molecular dynamics (MD) simulations. Information about interaction energies and non-covalent interactions formed between C24 and EPH have been obtained by DFT calculations. TD-DFT calculations have been used in order to obtain UV/vis spectra and to check whether the presence of the EPH molecule produces significant changes in the spectrum. The SAPT approach has been employed in order to decompose the interaction energy into components and therefore to better understand the physical origins of interaction between C24 and EPH. Last, but not least, MD simulations have been used in order to track the influence of temperature on the interactions between C24 and EPH.

The aggregation ability and exciton dynamics of dyes are largely affected by properties of the dye monomers. To facilitate aggregation and improve excitonic function, dyes can be engineered with substituents to exhibit optimal key properties, such as hydrophobicity, static dipole moment differences, and transition dipole moments. To determine how electron donating (D) and electron withdrawing (W) substituents impact the solvation, static dipole moments, and transition dipole moments of the pentamethine indocyanine dye Cy5, density functional theory (DFT) and time-dependent (TD-) DFT calculations were performed. The inclusion of substituents had large effects on the solvation energy of Cy5, with pairs of withdrawing substituents (W-W pairs) exhibiting the most negative solvation energies, suggesting dyes with W-W pairs are more soluble than others. With respect to pristine Cy5, the transition dipole moment was relatively unaffected upon substitution while numerous W-W pairs and pairs of donating and withdrawing substituents (D-W pairs) enhanced the static dipole difference. The increase in static dipole difference was correlated with an increase in the magnitude of the sum of the Hammett constants of the substituents on the dye. The results of this study provide insight into how specific substituents affect Cy5 monomers and which pairs can be used to engineer dyes with desired properties.

Ruthenium, osmium and rhodium complexes of 1,4-di(3-nitrophenyl)-1,4-diazabutadiene (LDAB) of types trans-[RuII(LDAB)(PPh3)2Cl2] (1), trans-[OsII(LDAB)(PPh3)2Br2] (2) and trans-[Rh(LDAB)(PPh3)2Cl2] (3) are isolated and characterized by elemental analyses, IR, mass and 1H NMR spectra including the single crystal X-ray structure determination of 1·2toluene. The α-diimine fragment of the LDAB ligand in 1·2toluene is deformed, showing a relatively longer -C=N- bond, 1.320 Å, and a shorter =CH–CH= bond, 1.395 Å. Density functional theory (DFT) calculations on trans-[Ru(LDAB)(PMe3)2Cl2] (1Me) and trans-[Os(LDAB)(PMe3)2Br2] (2Me) with singlet spin states authenticated that the closed shell singlet state (CSS) solutions of 1 and 2 are stable and no perturbation occurs because of the diradical open shell singlet (OSS) state. The EPR spectra of 3 and the Mulliken spin density distribution obtained from the DFT calculation on trans-[Rh(LDAB)(PMe3)2Cl2] (3Me) imply that the ground electronic state of 3 can be defined by the [RhIII(LDAB˙−)(PPh3)2Cl2] (3RhL˙) ↔ [RhII(LDAB)(PPh3)2Cl2] (3Rh˙L) resonating states. In solid, the contribution of 3RhL˙ is higher and the gav is 2.018 with Δg = 0.10, whereas in frozen glasses the contribution of 3Rh˙L is higher and the gav is 2.026 with Δg (frozen glasses) = 0.13. The g parameters of the electrogenerated [1]+ (g1 = 2.456, g2 = 2.128 and g3 = 1.624, Δg = 0.824), [2]+ (g1 = 2.599, g2 = 2.041 and g3 = 1.965, Δg = 0.634), [1]− (g1 = 2.138, g2 = 2.109, g3 = 1.978 and Δg = 0.160) and [2]− (g1 = 2.168, g2 = 2.097, g3 = 1.987 and Δg = 0.181) ions and the spin density distributions obtained from the DFT calculations on [1Me]+, [2Me]+, [1Me]− and [2Me]− reveal that the reversible anodic peaks of 1 and 2 at 0.11 and 0.34 V, referenced versus Fc+/Fc couple, are due to the M(III)/M(II) redox couple, while the reversible cathodic waves at −1.27 V and −0.82 V of 1 and 2 are caused by the LDAB/LDAB˙− redox couple. Both [MII(LDAB˙−)(PPh3)2Br2]− and [MI(LDAB)(PPh3)2Br2]− tautomers contribute to the ground electronic states of [1]− (g = 2.075) and [2]− (g = 2.084) ions, which are isoelectronic to 3. Time dependent (TD) DFT calculations and spectroelectrochemical measurements elucidated that lower energy absorption bands of 1 and 2 are caused by the metal to ligand charge transfer (MLCT) that disappears upon oxidation or reduction.

A theoretical study is presented on the adsorption of the sarin molecule, a nerve agent, on three model solid surfaces: aliphatic (graphane), aromatic (graphene), and ionic (CaO). Calculations are carried out using accurate electronic structure methods based on configuration interaction (CI) as well as complementary density functional theory (DFT) and time dependent (TD) DFT calculations. The objective is to describe surface interactions accurately in order to identify factors that affect adsorption of sarin. Potential energy curves are calculated and compared between surface types. Computed CI binding energies to graphane, graphene, and calcium oxide surfaces are 2.2, 4.5, and 13.2 kcal/mol, respectively. The corresponding DFT binding energies are 6.4, 4.8, and 18.8 kcal/mol, respectively. Excited states of free sarin as well as sarin bound to the surfaces are examined using TDDFT and CI. Low-lying excited states of the adsorption complexes involving excitations from the surface to sarin are calculated.

Spectroscopic and DFT/TD-DFT studies on selective and sensitive fluorescent detection of Al(III) ion

Cholesterol-based dimeric liquid crystals: synthesis, mesomorphic behaviour of frustrated phases and DFT study

The decomposition of and the stability of in organic solvents, diethyl carbonate (DEC), dimethyl carbonate (DMC), γ-butyrolactone (GBL), and ethylene carbonate (EC), have been investigated through density functional theory (DFT) calculations, in which solvent was modeled as a dielectric continuum, and also by molecular dynamics (MD) simulations which treated solvents explicitly. Both calculations showed a similar trend in which the decomposition was further promoted in more polar solvents, yet the DFT calculations predicted an endothermic decomposition, while the MD simulations indicated exothermic. This sharp contrast in the results suggests strong solute-solvent interactions, especially for which were not accounted for in the DFT calculations. The specific interaction between and solvent was further investigated by DFT calculations for adduct models and also by the MD simulations for solutions. Both calculations suggest a stable formation of a -solvent adduct in solution and its stability depends on the solvent. It was found that is more stabilized in polar and sterically compact solvents such as EC and GBL than in less polar and bulky, linear carbonates such as DMC and DEC. The reactivity of with organic solvents and the difference in the stability of between organic and aqueous solution are also discussed. © 2003 The Electrochemical Society. All rights reserved.

In this study, the full reaction mechanism for N2O hydrogenation on silver doped Au(210) surfaces was investigated in order to clarify the experimental observations. Density functional theory (DFT) calculations were used to state the most favorable reaction paths for individual steps involved in the N2O hydrogenation. From the DFT results, the activation energy barriers, rate constants and reaction energies for the individual steps were determined, which made it possible to elucidate the most favorable reaction mechanism for the global catalytic process. It was found that the N2O dissociation occurs in surface regions where silver atoms are present, while hydrogen dissociation occurs in pure gold regions of the catalyst or in regions with a low silver content. Likewise, N2O dissociation is the rate determining step of the global process, while water formation from O adatoms double hydrogenation and N2 and H2O desorptions are reaction steps limited by low activation energy barriers, and therefore, the latter are easily carried out. Moreover, water formation occurs in the edges between the regions where hydrogen and N2O are dissociated. Interestingly, a good dispersion of the silver atoms in the surface is necessary to avoid catalyst poison by O adatoms accumulation, which are strongly adsorbed on the surface.

Dimethyl fumarate molecule, crystal, and plane: Optical absorption measurement and structural/optoelectronic properties by density functional theory calculations

Topological nodal line semimetal PdSn4 is investigated through high-pressure Raman spectroscopy, corroborated by first principles density functional theory (DFT) calculations. At ambient conditions, the Raman spectrum shows a broad peak structure at around 130 cm−1 together with several weak peaks. DFT calculations within the Ccce orthorhombic structure identify the 12 possible Raman active modes in this system below 140 cm−1, correlating well with the experimental observation. A comparison of the Raman spectra of RSn4 (R = Pd, Pt, and Au) showed a similar broad peak-like structure with slightly differing wavenumbers in agreement with a chemical pressure description of these systems. Indeed, phonon dispersions from DFT studies within the Ccce orthorhombic structure provided similar phonon band structures for both PdSn4 and PtSn4 and demonstrate that the orthorhombic lattice of PdSn4 to be stable at 25 GPa. In this pressure range, DFT as well as experiments showed a regular hardening of the Raman phonon modes. A careful analysis indicates that the pressure dependence of the mode positions has a different rate in the high- and low-pressure regions. This is an indication of a pressure-dependent isostructural phase transition in PdSn4, similar to that observed in PtSn4.

Density functional theory (DFT) calculations for the methanol oxidation reaction (MOR) has attracted much more attention than ever before, since the mechanism of methanol dehydrogenation is very important in direct methanol fuel cell (DMFC). Herein, methanol adsorption on Pd(111) with different electric field intensity (0.000, 0.0010, 0.0025 and 0.0050 au) were studied with DFT calculations. The results showed that methanol may adsorb on the Pd(1 1 1) either through the methyl or the hydroxyl of methanol in the absence electric field, since the two adsorption configurations share the similar adsorption energy. However, along with the increase of the electric field intensity, the angles formed by C-O bond axis and Pd(1 1 1) became gradually smaller, and it is only 1.9° when the electric field intensity value is 0.0050 au for the methyl case; while it kept at 35±5° for the hydroxyl case. The methanol molecule was not activated in the reported electric field.

New mixed valence gold(III/I) salt containing two complexes [Au(Me2phen)Br2][AuBr2] (1) was prepared from the reaction of AuBr3 and 5,6-dimethyl-1,10-phenanthroline (Me2phen) in a mixture of methanol and acetonitrile. Suitable crystals of 1 for X-ray diffraction measurement were obtained by slow evaporation of the resulted red solution at room temperature. This complex was characterized by spectral methods (IR, UV–Vis and 1H NMR), elemental analysis and single-crystal X-ray diffraction. The X-ray structural analysis indicated that the asymmetric unit of 1 contains one [Au(Me2phen)Br2]+ cation and two half anions of [AuBr2]ˉ. Furthermore, the packing diagram of this complex, 3-D structure stabilized by intermolecular Au…Br and Au…π interactions and intermolecular C–H···Br hydrogen bonds. The experimental investigations on complex have been accompanied computationally by the density functional theory (DFT) and time-dependent DFT calculations. The nature of the Au–N bonds was investigated using quantum theory of atoms in molecules. Moreover, natural bond orbital analysis carried out to obtain hyper-conjugative interactions and electron delocalization on the complex.

We theoretically analyze the optoelectronic properties of single crystals of 2,5-bis(4-biphenylyl) bithiophene (BP2T) and 2-(4-biphenyl)-5-[5-(4-biphenyl)-2-thienyl] furan (BPFT) molecules, aiming to provide a guiding principle for the material design of organic light-emitting transistors. The X-ray structure analysis and the density functional theory (DFT) calculations indicate that half of the BPFT molecules bend the π-conjugation plane in the crystal. The Marcus theory parametrized by the DFT calculations indicates anisotropic charge mobilities. The emission spectra of the BP2T and BPFT crystals are analyzed by the time-dependent DFT calculations in conjunction with the Frenkel exciton model and the vibronic coupling analysis. We revealed that the high photoluminescence efficiency of the BPFT crystal originates from the symmetry breaking of the H-aggregate, where the transition dipole of the dark state does not cancel out.

Structures and properties of metal-free and copper tetrakis(thiadiazole) porphyrazine and metal-free tetrakis(selenodiazole) porphyrazine based on density functional theory calculations

Oxidative dehydrogenation of ethanol on gold: Combination of kinetic experiments and computation approach to unravel the reaction mechanism