Stable Molecular Configuration Research Articles

Structural and spectroscopic features of naphthol green B integrated for improved light harvesting capability of organic/inorganic hybrid solar cells

Regarding the intensified interest in photovoltaic devices for a wide range of applications, here, we exploited a promising naphthol green organic dye for designing efficient organic/inorganic heterojunction for solar cell applications. The crystal and molecular structures of the spin-coated NGB thin films were inspected using XRD and FTIR techniques, respectively. A nanostructured polycrystalline film was obtained with a crystallite size of ∼76.2 nm with a stable molecular configuration. The optical properties of the films were analyzed using spectrophotometrically measured transmission and reflection. The prepared films showed high absorption over the UV–Vis–NIR regimes with a relatively small energy gap of ∼1.42 eV and a low refractive index of ∼1.48 which increased its suitability for photosensing applicability. The photovoltaic performance of the fabricated Ag/NGB/p-Si/Al heterojunction was evaluated in detail yielding promising photovoltaic characteristics with Voc ∼0.77 V, Jsc ∼18.64 mA/cm2, and PCE ∼6.49 %.

Extensively amino-functionalized graphene captures carbon dioxide.

The development of robust carbon dioxide (CO2) scavengers is a challenging but paramount problem of modern humanity. In the present work, we report a prospective CO2 sorbent based on amino-functionalized graphene (FG). Amino-FG retains the favorable physicochemical properties of graphene and acquires the capability of chemically fixing CO2via the carbamic acid formation mechanism. In the present work, we comprehensively investigate CO2 capturing prospects by extensively amino-FG using hybrid density functional theory. We show that up to six amino groups can be grafted, remain stable, and subsequently chemisorb CO2 per benzene ring. Two functional groups above the benzene ring and four such groups below the benzene ring represent a thermodynamically stable molecular configuration in which the number of carbon atoms is equal to the number of functional groups. The thermochemistry of chemisorption is, in general, negatively impacted by the increase in the density of functional groups. However, a less favorable Gibbs free energy is compensated by a several fold higher number of prospective reaction sites. The thermochemistry results are rationalized by considering steric hindrances on the surface of graphene in the context of the states of hybridization and genuine geometries of the amino- and carboxamido functional groups. The functionalization and chemisorption decrease the hydrophobicity of graphene derivatives and, therefore, foster the development of novel and more robust chemical engineering setups.

In Search of the Most Stable Molecular Configuration of Heptakis(2,6-O-dimethyl)-β-cyclodextrin and Its Complex with Mianserin: A Comparison of the B3LYP-GD2 and M062X-GD3 Results.

Cyclodextrins are well known for their ability to form stable, highly soluble complexes with various substances, which makes them widely used as excipients in food, cosmetics, and pharmaceuticals. In this work, properties of heptakis(2,6-O-dimethyl)-β-cyclodextrin (DM-β-CD) in vacuo and in water, as well as its ability to bind the antidepressant drug mianserin (MIA) in aqueous solution, are investigated computationally. The results are shown to depend strongly on the density functional theory (DFT) applied. The most stable conformers of DM-β-CD found with the B3LYP-GD2 method differ from these indicated by M062X-GD3 and other functionals. According to the latter, two crystal structures, ZULQAY and BOYFOK03, optimized in vacuo and in water, respectively, have the lowest energy. Both the B3LYP-GD2 and M062X-GD3 results show that all tested inclusion and noninclusion complexes of MIA:DM-β-CD in stoichiometry 1:1 are stable in water. However, the structures and their energetic properties obtained with each method differ: in the most stable configurations, different aromatic rings of MIA are embedded inside DM-β-CD, and the corresponding complexation energies (calculated with the 6-31++G(d,p) basis set and corrected for the basis set superposition error) are −29.6 (B3LYP-GD2) and −23.9 (M062X-GD3) kcal/mol. The NMR spectra of DM-β-CD and MIA:DM-β-CD are also compared.

Molecular structural characteristics of late Jurassic Shengli lignite submacerals

Different lignite submacerals have complex physical and chemical properties, and exploring their molecular structures are of great significance for enrichment the evolution mechanism of coal microstructure and efficient utilization. In this paper, raw lignite with rich-(eu-ulminite) (FJ) and rich-leviglinite (FW), respectively, were selected on the basis of petrographic identification. The proximate analysis and ultimate analysis, FTIR, XPS, 13C NMR, HRTEM and molecular simulation technique were used to construct the molecular structure of FJ and FW. The experimental data and molecular structural models show that FW has a higher aromaticity, larger size of the aromatic layer, and more pronounced directional arrangement. In a single stable molecular configuration, aromatic rings and the aliphatic ring are arranged in a wrapped arrangement. Furthermore, the type of hydrogen bond mainly depends on the type of oxygen-containing functional group of the molecular structure. In addition, the length and angle of the hydrogen bond tend to be polarized. There is a little difference on the value of experimental and simulated density.

Electronic, reactivity and third order nonlinear optical properties of thermally-stable push-pull chalcones for optoelectronic interest: Experimental and DFT assessments

The present work highlighted the integration of quantum chemical approach and experimental results in attempts to elucidate the structural-property characteristics and behaviour of the fused-aromatic chalcones on the impact of their nonlinear attribute at the molecular level. Two push-pull chalcones namely 1-(anthracen-9-yl)-3(9-ethyl-carbazol-3-yl)prop-2-en-1-one (1AECP) and 3(9-ethyl-carbazol-3-yl)-1(pyren-1-yl)prop-2-en-1-one (3ECPP) were successfully designed, synthesised and analysed through FT-IR, UV–Vis, 1D NMR, TGA, DSC and third-order optical nonlinearities were performed via Z-scan measurement. Concurrently, density functional theory (DFT) analysis with basis set of B3LYP/6-31G (d,p) was computed to optimize the most stable molecular geometry configuration, HOMO-LUMO energy gap, global chemical reactivity descriptors (GCRD), molecular electrostatic potentials (MEP), natural bond orbital (NBO) analysis and hyperpolarizability analyses. The experimental optical gap (Egopt) of both compounds has demonstrated good agreement with corresponding calculated result and fall in the range of organic semiconducting materials with low range of HOMO-LUMO energy gap values, 2.98 and 2.74 eV respectively. The DFT result revealed that fused-aromatic reinforce intramolecular charge transfer (ICT), electronic dipole moment and improve polarizabilities on NLO properties of the material. The thermal stability analysis pinpointed that both of these materials are able to withstand high temperature up to 300 °C which unintentionally unveil their encouraging performance potentially. Additionally, Z-scan analysis discovered that both of the targeted compounds are indeed nonlinear refraction (NLR) active, manifesting self-defocusing effect with n2 value of −1.75 x 10−9 esu (1AECP) and −1.75 x 10−8 esu (3ECPP). In short, the theoretical output complement the experimental results fundamentally in the evaluation and prediction of their electronic nature which hence proved their prospect essentially in the optoelectronic-manufacturing development.

Activation of CO2 on graphitic carbon nitride supported single-atom cobalt sites

Using solar energy to realize photoreduction of CO2 into valuable chemicals is a potential way to solve energy crisis and carbon cycle. Due to the extremely stable molecular configuration of CO2, activating CO2 molecule is the key and difficult step in the whole CO2 conversation process. In this work, we used density functional theory (DFT) to calculate the reaction pathways of CO2 to CO on pure g-C3N4 and single-atom cobalt (Co) modified g-C3N4. Theoretical calculation predicts that single-atom Co sites modified g-C3N4 (Co-CN) possess stronger CO2 adsorption ability and lower barrier of CO2 hydrogenation activation than pure g-C3N4. The strong interaction between Co 3d electrons and C 2p electrons of CO2 is the crucial factor to activate C = O bonds of CO2 molecule. Better CO2 adsorption and activation abilities also are proved in Co-CN by CO2 adsorption, temperature programmed desorption (TPD), and sensor tests. As a result, the optimal 1%Co-CN exhibits higher CO yield of 94.9 umol/g/h than pure g-C3N4 (0.25 umol/g/h). This work provides a new insight of the role of single-atom sites in CO2 reduction reactions.

Electronic structure and adsorption geometry of Pt and Pd metal complexes with 1,3-dithiole-2-thione-4,5-dithiolate ligand on TiO2(101) surface from first-principles calculations

Metal complexes based on 1,3-dithiole-2-thione-4,5-dithiolate (dmit) ligand have been intensively studied for more than 40 years due to their unusual chemical and physical properties. Besides, the highly delocalized frontier orbitals, that allow direct electron transfer through the ligand π orbitals, make these class of complexes promising candidates for photochemical devices as well as sensitizer for dye-sensitized solar cells. In this work, we investigated the electronic and geometric properties of Pd and Pt (CH3)2[M(dmit)2] complexes isolated on TiO2(101) surface by means of first-principles calculations using plane-wave basis sets and DFT calculation. Adsorption energies of metal complexes supported on a TiO2(101) surface are calculated for three different configurations, linked by the sulfur atom of Sthione, Sthiole–Sthiolate, and planar. The studies found that the most stable adsorption molecular configuration mode for the palladium(II) and platinum(II) complexes is the planar mode. TD-DFT molecular calculations revealed that the lowest energy transition in the ultraviolet visible near-infrared range mainly corresponds to the HOMO–LUMO excitation for the (CH3)2[M(dmit)2] complexes. Theoretical calculations of optical absorption spectra of (CH3)2[M(dmit)2] complexes adsorbed on the anatase (101) surface show that the interaction induces a slightly redshift of electronic absorption bands. Density of states for the metal complexes/TiO2(101) system revealed that the LUMO of the metal complexes lies at below the edge of the TiO2 conduction band. The adsorption of the (CH3)2[Pd(dmit)2] complex on the anatase (101) surface results in the emergence of new transitions below 1 eV that can be ascribed to the presence of a favorable overlap between the LUMO of the complex and the conduction band of the TiO2 semiconductor.

Performance enhancement using a stable low-pretilt molecular configuration and a novel driving method for optically compensated bend liquid crystal devices.

A stable low-pretilt molecular configuration (SLPMC) is successfully developed in optically compensated bend (OCB) liquid crystal (LC) devices by simultaneously employing the curing voltage and surface-anchored crosslinking monomer during the polymerization process. For the SLPMC OCB cell with the low-bend state, the warm-up voltage making the LC molecules reorient from the splay to the bend state is annihilated, and the transient twist state occurring as the driven LC molecules recover from the bend to the splay state is also eliminated. In addition, with the novel driving method selecting the specific driving point, the proposed SLPMC OCB cell not only exhibits a good response performance, but also outputs a higher light transmittance, which is superior to the conventional OCB and no-bias-bend cells. This Letter demonstrates an effective SLPMC fabrication method, and points out the significant contributions of SLPMC on the electro-optical properties, which will benefit and enhance the performance design in OCB-based applications.

Effects of Molecular Configuration and Driving Architecture on Electro-Optical Properties of Cholesteric Liquid Crystal Displays

The effects of molecular configuration and driving architecture on the electro-optical properties of cholesteric liquid crystal (ChLC) displays are demonstrated. Two kinds of ChLC cells, composed by mixing the chiral dopant with the positive nematic LC (P-ChLC cell) and with the negative nematic LC (N-ChLC cell), are fabricated in order to make a detailed investigation. Compared with the conventional P-ChLC cell driven by the uniform vertical electric fields, the N-ChLC cell driven by the in-plane switching electric fields shows a higher output light transmittance and a more stable helical molecular configuration, which is attributed to the fact that the focal conic configuration does not exist in the N-ChLC cell. In addition, via the three-terminal-electrode driving architecture, a faster switching response (5.2 ms) of the N-ChLC cell at a low driving voltage is successfully achieved. This study not only exhibits the difference in the electro-optical properties of the P-ChLC and N-ChLC cells, but also provides a driving method for the N-ChLC cell to enhance its electro-optical performance, which is beneficial to the development of fast dynamic optical devices.

DFT Studies on the Electronic Spectrum and the Second-Order Nonlinear Optical Properties of Donor-Acceptor Helicenes

A series of chiral donor-acceptor helicenes have been designed using the molecular engineering of organic nonlinear optical materials. The geometries of donor-acceptor helicenes 1, 2, 3, 4, 5 are optimized using density functional theory (DFT-B3LYP) method at the 6-31g (d, p) basis set level. Based on the obtained stable molecular configuration, we adopt the TDHT/PM3 method and time-dependent density-functional theory (TD-DFT) to calculate the nonlinear optical (NLO) properties and electronic spectra of these molecules. Results show that molecule 4 has the largest static hyperpolarizability βμ of 40.4×10-30esu, which is enhanced by its two charge transfer orientations. In molecule 2, there exists two competitive charge transfers that weaken the second-order nonlinear optical effect of D-π-A structures greatly. The structural type of molecule 3, 4 and 5 are expected to be more efficient to achieve large β values.

Study on the Second-Order Nonlinear Optical Properties of [6]Helicenes with Chromophores

A series of chiral [6]helicenes have been designed using the molecular engineering of organic nonlinear optical materials. The geometries of [6]helicenes 1, 2, 3, 4,5 are optimized using density functional theory (DFT-B3LYP) method at the 6-31g (d, p) basis set level. Based on the obtained stable molecular configuration, we adopt the TDHT/PM3 method and time-dependent density-functional theory (TD-DFT) to calculate the nonlinear optical (NLO) properties and electronic spectra of these molecules. Results show that the static hyperpolarizability βµ alternates between positive value and negative value, whereas it remains positive for the molecues 2 and 3 which have medium magnitudes βµ, 3.4×10-30esu and 9.6×10-30esu respectively. In molecule 5, there exists two competitive charge transfers that reduce the hyperpolarizability β.

Second-Order Nonlinear Optical Properties of a Series of Y-Shaped Organic Molecules with a Thiazole Chromophore

Density functional theory (DFT) B3LYP/6-31G* method was employed to optimize the structures of a series of Y-shaped organic heterocyclic molecules containing a thiazole chromophore. Based on the obtained stable molecular configuration, we adopted the finite field (FF) method and time-dependent density-functional theory (TD-DFT) to calculate and analyze the nonlinear optical (NLO) properties and electric spectra of these molecules. Results show that the molecules possess A-π-D-π-A (A: acceptor, D: donor) structures, and the dipole moment of the ground state, the polarizability, and the second-order NLO coefficient (β) of the molecules increase with increase of the length of conjugate bridge of the branched chain and the conjugation effect of the chromophore. The total virtual value of second-order polarizability (βtot) of the series of organic heterocyclic molecules was found to be related to the energy gap of the frontier molecular orbital. The molecule with smaller energy gap of the frontier molecular orbital shows larger values of βtot.

Molecular oxygen on the Si(111)-7×7 surface

The adsorption of neutral molecular oxygen at room temperature on the Si(111)-7\ifmmode\times\else\texttimes\fi{}7 surface has for more than 20 years been a central issue in physics and chemistry as it offers a unique model system for surface reactions with a maximum number of observable parameters. A comprehensive set of new details of this system come from synchrotron radiation induced photoelectron spectroscopy, in terms of changes of the population of the surface states and of the number of chemically shifted atoms at the surface. The reaction steps between oxygen molecules and different surface bonds and atoms in the unit cell are now followed in full detail including the existence of a stable molecular configuration up to exposures of 6 L.

Molecular resonance and highly deformed fission fragments in28Si+28Si

A high-resolution measurement of fragment-fragment-$\ensuremath{\gamma}$ triple coincidence events in the symmetric and near-symmetric mass exit channels from the ${}^{28}\mathrm{Si}{+}^{28}\mathrm{Si}$ reaction has been undertaken using the EUROGAM Phase II $\ensuremath{\gamma}$-ray spectrometer. The bombarding energy of ${E}_{\mathrm{lab}}{(}^{28}\mathrm{Si})=111.6 \mathrm{MeV}$ has been selected to populate the conjectured ${J}^{\ensuremath{\pi}}{=38}^{+}$ quasimolecular resonance in the ${}^{56}\mathrm{Ni}$ dinuclear system. In the ${}^{28}\mathrm{Si}{+}^{28}\mathrm{Si}$ symmetric mass exit channel, the resonance behavior is clearly verified at the chosen energy. The population of highly excited states in the ${}^{24}\mathrm{Mg},$ ${}^{28}\mathrm{Si},$ and ${}^{32}\mathrm{S}$ nuclei is discussed within a statistical fusion-fission model. Evidence is presented for selective population of states in the ${}^{28}\mathrm{Si}$ fragments arising from the symmetric fission of the ${}^{56}\mathrm{Ni}$ compound nucleus. The enhanced population of the ${K}^{\ensuremath{\pi}}{=3}_{1}^{\ensuremath{-}}$ band of the ${}^{28}\mathrm{Si}$ nucleus, indicative of an oblate deformed shape, suggests that the oblate configuration plays a significant role in the resonant process. Fragment angular distributions for the elastic and low-lying inelastic channels as well as $\ensuremath{\gamma}$-ray angular correlations for the mutual inelastic channel ${(2}^{+}{,2}^{+})$ indicate that the spin orientations of the outgoing fragments are perpendicular to the orbital angular momentum. This unexpected result, which is different from the alignment found for the resonance structures in the ${}^{24}\mathrm{Mg}{+}^{24}\mathrm{Mg}$ and ${}^{12}\mathrm{C}\mathrm{}{+}^{12}\mathrm{C}$ systems, suggests a situation where two oblate ${}^{28}\mathrm{Si}$ nuclei interact in an equator-to-equator stable molecular configuration. A discussion concerning the spin alignment and spin disalignment for different reactions such as ${}^{12}\mathrm{C}\mathrm{}{+}^{12}\mathrm{C},$ ${}^{24}\mathrm{Mg}{+}^{24}\mathrm{Mg},$ and ${}^{28}\mathrm{Si}{+}^{28}\mathrm{Si}$ is presented.

The energetics of adsorption of HCOOH on the MgO(100) surface

Ab initio calculations based on density functional theory and the pseudopotential method have been used to investigate the adsorption of HCOOH (formic acid) on the flat non-defective MgO(100) surface. The aims of the work are to find the energetically most favorable adsorbed configurations, and to determine whether dissociative adsorption is favorable. The calculations are performed in slab geometry using periodic boundary conditions. They are fully converged with respect to the size of the plane-wave basis set, and full relaxation of all atoms in the system is performed throughout. Results obtained both with the local density approximation and including generalized gradient corrections are presented. It is found that the most stable configuration is dissociative, with the formate ion symmetrically attached via its oxygen atoms to two surface Mg ions. This configuration is more stable than the most stable molecular configuration by ∼0.3 eV. The energy barrier separating molecular and dissociated adsorbed configurations is small, so that spontaneous dissociation would occur under all conditions of interest. The relations between our findings and previous experimental and theoretical results are discussed.

A new interpretation of plasmodesmatal ultrastructure

It is shown that simple, unbranched, plasmodesmata between young xylem ray cells of willow have no direct intercellular continuity apart from the plasmalemma which limits the cytoplasm and lines the plasmodesmatal canal. Each plasmodesma is traversed by a 200 Å diameter tubule (the desmotubule) which has a wall with probably 11 subunits arranged around a central cavity through which runs a 40 Å diameter rod. This rod is connected to the inside of the tubule wall, by fine filaments. At the ends of each plasmodesma the plasmalemma and cell wall are closely appressed to the tubule, thus precluding direct continuity between the cytoplasm of adjacent cells. Through the central part of the plasmodesmata the tubule is separated from the plasmalemma by a 90-100 Å wide gap. Cytoplasmic microtubules in the same tissue have a diameter of approximately 250 Å and a wall probably composed of 13 subunits: both desmotubules and cytoplasmic microtubules therefore have a centre-to-centre subunit spacing of about 47 Å. It is suggested that the desmotubules are not microtubules but may be nuclear spindle fibres which become trapped in the wall during cell plate formation. The endoplasmic reticulum, while closely approaching the plasmodesmata, is not continuous across them. It is thought most unlikely that the endoplasmic reticulum traverses plasmodesmata, as the dimensions of the central tubule - found here as well as by other workers - are smaller than those which would be expected to allow a stable molecular configuration in a unit membrane. The plasmalemma, where it lines the plasmodesmatal canal, appears to have particulate subunits in the outer opaque layers and the presence of these subunits may be attributable to the need for stability in membranes arranged about so small a radius.

ELECTRONIC PROPERTIES AND PHOTOCHEMICAL MONOMOLECULAR REACTIONS IN ORGANIC CONJUGATED COMPOUNDS: PHOTOCYCLIZATIONS, PHOTOISOMERIZATIONS AND PHOTOCHEMICAL REARRANGEMENTS—I

Abstract— It is assumed that quantum yields of monomolecular reactions are mainly determined by the probability of de‐excitation from the excited state to the ground state of the photoproduct and that a reaction will occur only if the stable molecular configuration of the excited state is close enough the molecular configuration of the photoproduct. In order to evaluate the stabilizing deformation of the excited states, the different methods of representing the excited states wave‐functions are compared. Though very different in their ability to reproduce spin densities in the triplet state, these methods appear to give very close results for the electronic repartition; particularly, unrestricted Hartree‐Fock calculations seem to give nearly the same net charges and bond indices for corresponding singlet and triplet states. A simple method for a rough evaluation of the direction and of the amplitude of the stabilizing deformation is proposed. In the Hiickel scheme, the variations in bond orders may be taken as an approximate index of that deformation.