Theoretical Study of Solvent Effects on the Electronic and Thermodynamic Properties of Tetrathiafulvalene (TTF) Molecule Based on DFT

Tetrathiafulvalene () is an organosulfur compound used in the production of molecular devices such as switches, sensors, nonlinear optical devices and rectifiers. In this work, a theoretical study on the effects of solvent on TTF molecule was investigated and reported based on Density Functional Theory (DFT) as implemented in Gaussian 03 package using B3LYP/6-31++G(d,p) basis set. Different solvents were introduced as a bridge to investigate their effects on the electronic structure. The HUMO, LUMO, energy gap, global chemical index, thermodynamic properties, NLO and DOS analysis of the TTF molecule in order to determine the reactivity and stability of the molecule were obtained. The results obtained showed that the solvents have effects on the electronic and non-linear-optical properties of the molecule. The optimized bond length revealed that the molecule has strong bond in gas phase with smallest bond length of about 1.0834Å than in the rest of the solvents. It was observed that the molecule is more stable in acetonitrile with HOMO-LUMO gap and chemical hardness of 3.6373eV and 1.8187eV respectively. This indicates that the energy gap and chemical hardness of TTF molecule increases with the increase in polarity and dielectric constant of the solvents. The computed results agreed with the results in the literature. The thermodynamics and NLO properties calculation also indicated that TTF molecule has highest value of specific heat capacity (Cv), total dipole moment () and first order hyperpolarizability () in acetonitrile, while acetone has the highest value of entropy and toluene has a slightly higher value of zero point vibrational energy (ZPVE) than the rest of the solvents. The results show that careful selection of the solvents and basis sets can tune the frontier molecular orbital energy gap of the molecule and can be used for molecular device applications.

Classical physical mechanism of quantum production and its explanation for hydrogen atom structure and photoelectric effect

In this paper, the problems existing in the concepts of Planck's energy element and Einstein's light quantum are analyzed, and the alternate concept of quantum and a new concept of electron transition power were proposed. This paper clarifies the common misunderstanding in classical electromagnetics that the electron will radiate electromagnetic wave when it moves around the nucleus in a uniform circular motion and points out that the electron will radiate and absorb electromagnetic waves only when it moves around the nucleus in an accelerated or decelerated motion with a change of frequency and expounds the classical physical mechanism of quantum generation. Based on this, the quantization of electron orbital energy level of hydrogen atom and the phenomenon of spectrum are explained without Bohr's “quantization hypothesis.” In addition, the photoelectric effect is explained by using the modified quantum concept. The modified quantum concept and its mechanism of classical physics break the gap between macro and micro physics, eliminate the contradiction between “classical physics” and “quantum mechanics,” and lay an important foundation for the reconstruction of unified macro and micro physics.

Active sites of peptide from Arg-Ser-Ser protect against oxidative stress in HepG2 cells

Peptide Arg-Ser-Ser (RSS) was derived from Lactobacillus amylolyticus co-incubated with edible <i>Dendrobium aphyllum</i>. Here, we further examined the antioxidative effects of RSS in HepG2 cells subjected to 2,2-azobis(2-methylpropanimidamidine) dihydrochloride-induced oxidative stress. RSS protected cells by eliminating the level of reactive oxygen species (ROS). The protein expression of antioxidant enzymes, Nrf2 and Keap1 determined by western blot, indicated that RSS might maintain cellular homeostasis by directly scavenging free radicals instead of by enzymatic system. Furthermore, quantum chemistry calculations and a characterization of electronic-related properties showed that the highest occupied molecular orbital energy distribution was on arginine residue. Pre-treatment with RSS with the active site methylated resulted in increased ROS levels, thereby verifying that N₂-H₃ is the active site for antioxidant activity. Our findings provide valuable insights into the antioxidant activity of RSS and a basis for developing antioxidant functional foods.

Synthesis, Photophysical, Electrochemical, and DFT Examinations of Two New Organic Dye Molecules Based on Phenothiazine and Dibenzofuran

New dyes were developed and produced utilizing distinct electron donors (phenothiazine and dibenzofuran), a p-spacer, and an electron acceptor of cyanoacetohydrazide, and their structures were studied using FT-IR and NMR spectroscopy. Following the synthesis of dye molecules, the photophysical and photovoltaic characteristics were investigated using experimental and theoretical methods. The photosensitizers have been exposed to electrochemical and optical property experiments in order to study their absorption performance and also molecular orbital energies. The monochromatic optical conversion efficiency of (Z)-N-((5-(10H-phenothiazin-2-yl)furan-2-yl)methylene)-2-cyanoacetohydrazide (PFCH) found higher than that of (Z)-2-cyano-N'-((5-(dibenzo[b,d]furan-4-yl)furan-2-yl)methylene)acetohydrazide (BFCH), with IPCEs of 58 and 64% for BFCH and PFCH, respectively. According to the photosensitizer molecular energy level diagram, the studied dye molecules have strong thermodynamically advantageous ground and excited state oxidation potentials for electron injection into the conduction band of titanium oxide. It was observed that the ability to attract electrons correlated favorably with molecular orbital energy. While density functional theory calculations were used to examine molecule geometries, vertical electronic excitations, and frontier molecular orbitals, experimental and computed results were consistent. Natural bond orbital and nonlinear optical properties were also calculated and discussed.

Predicting Finite-Bias Tunneling Current Properties from Zero-Bias Features: The Frontier Orbital Bias Dependence at an Exemplar Case of DNA Nucleotides in a Nanogap

The electrical current properties of single-molecule sensing devices based on electronic (tunneling) transport strongly depend on molecule frontier orbital energy, spatial distribution, and position with respect to the electrodes. Here, we present an analysis of the bias dependence of molecule frontier orbital properties at an exemplar case of DNA nucleotides in the gap between H-terminated (3, 3) carbon nanotube (CNT) electrodes and its relation to transversal current rectification. The electronic transport properties of this simple single-molecule device, whose characteristic is the absence of covalent bonding between electrodes and a molecule between them, were obtained using density functional theory and non-equilibrium Green’s functions. As in our previous studies, we could observe two distinct bias dependences of frontier orbital energies: the so-called strong and the weak pinning regimes. We established a procedure, from zero-bias and empty-gap characteristics, to estimate finite-bias electronic tunneling transport properties, i.e., whether the molecular junction would operate in the weak or strong pinning regime. We also discuss the use of the zero-bias approximation to calculate electric current properties at finite bias. The results from this work could have an impact on the design of new single-molecule applications that use tunneling current or rectification applicable in high-sensitivity sensors, protein, or DNA sequencing.

Energy flows in tight focus of optical vortices

In this paper we investigated tight focusing of optical vortex with topological charge m = 2 and left circular polarization. The simulation was based on Richards-Wolf equation. Light with wavelength 532 nm was focused by aplanatic lens with numerical aperture NA=0.95. It was shown that the longitudinal component of Poynting vector has negative values on the optical axis. The reason of the energy backflow is due to the fact that the projection of the spin flow onto the optical axis is negative and exceeds in absolute value the projection of the orbital energy flow, which is always positive.

Charge Transfer Complexes of 1,3,6-Trinitro-9,10-phenanthrenequinone with Polycyclic Aromatic Compounds

Understanding the interactions of organic donor and acceptor molecules in binary associates is crucial for design and control of their functions. Herein, we carried out a theoretical study on the properties of charge transfer complexes of 1,3,6-trinitro-9,10-phenanthrenequinone (PQ) with 23 aromatic π-electron donors. Density functional theory (DFT) was employed to obtain geometries, frontier orbital energy levels and amounts of charge transfer in the ground and first excited states. For the most effective donors, namely, dibenzotetrathiafulvalene, pentacene, tetrathiafulvalene, 5,10-dimethylphenazine, and tetramethyl-p-phenylenediamine, the amount of charge transfer in the ground state was shown to be 0.134−0.240 e−. Further, a novel charge transfer complex of PQ with anthracene was isolated in crystalline form and its molecular and crystal structure elucidated by single-crystal synchrotron X-ray diffraction.

d- and s-orbital populations in the d block: unbound atoms in physical vacuum versus chemical elements in condensed matter. A Dronskowski-population analysis

The electron configurations of Ca, Zn and the nine transition elements M in between (and their heavier homologs) are reviewed on the basis of density functional theory and experimental facts. The d-s orbital energy and population patterns are systematically diverse. (i) The dominant valence electron configuration of most free neutral atoms M0 of groups g = 2–12 is 3d g−2 4s 2 (textbook rule), or 3d g−14s 1. (ii) Formal M q+ cations in chemical compounds have the dominant configuration 3d g−q 4s 0 (basic concept of transition metal chemistry). (iii) M0 atoms in metallic phases [M∞] of hcp, ccp(fcc) and bcc structures have intermediate populations near 3d g−1 4s 1 (lower d populations for Ca (ca. ½) and Zn (ca. 10)). Including the 4p valence orbitals, the dominant metallic configuration is 3d g−δ 4(sp) δ with δ ≈ 1.4 (±0.2) throughout (except for Zn). (iv) The 3d,4s population of atomic clusters M m varies for increasing m smoothly from single-atomic 3d g−24s 2 toward metallic 3d g−14s 1. – The textbook rule for the one-electron energies, i.e., ns < (n−1)d, holds ‘in a broader sense’ for the s block, but in general not for the d block, and never for the p block. It is more important to teach realistic atomic orbital (AO) populations such as the ones given above.

Fischer–Tropsch Synthesis: Effect of the Promoter’s Ionic Charge and Valence Level Energy on Activity

In this contribution, we examine the effect of the promoter´s ionic charge and valence orbital energy on the catalytic activity of Fe-based catalysts, based on in situ synchrotron X-ray powder diffraction (SXRPD), temperature-programmed-based techniques (TPR, TPD, CO-TP carburization), and Fischer–Tropsch synthesis catalytic testing studies. We compared the promoting effects of K (a known promoter for longer-chained products) with Ba, which has a similar ionic radius but has double the ionic charge. Despite being partially “buried” in a crystalline BaCO3 phase, the carburization of the Ba-promoted catalyst was more effective than that of K; this was primarily due to its higher (2+) ionic charge. With Ba2+, higher selectivity to methane and lighter products were obtained compared to the K-promoted catalysts; this is likely due to Ba´s lesser capability of suppressing H adsorption on the catalyst surface. An explanation is provided in terms of a more limited mixing between electron-filled Ba2+ 5p and partially filled Fe 3d orbitals, which are expected to be important for the chemical promotion, as they are further apart in energy compared to the K+ 3p and Fe 3d orbitals.