Physicochemical properties and density functional theory calculation of octahedral UiO-66 with Bis(Trifluoromethanesulfonyl)imide ionic liquids

In this study, the physicochemical properties and molecular interactions between zirconium-based metal-organic framework (UiO-66) and three different ionic liquids based on bis(trifluoromethanesulfonyl)imide anion (EMIM+, BMIM+ and OMIM+) was performed via a combined experimental and computational approach. The ionic liquid loaded UiO-66 or IL@UiO-66 was synthesized and characterized to understand the host-guest interaction. Density functional theory calculation was performed to analyse the electronic structure of IL@UiO-66 to provide molecular insight on the dominant interactions occurred in the hybrid material. Results showed that all ILs were successfully incorporated into the micropores of UiO-66. The 3D framework was retained even after loaded with ILs as analyzed from XRD pattern. FTIR spectrum reveals that interactions of ILs with UiO-66 influenced by the alkyl chain length of the cation. The anion has a profound affinity with the UiO-66 due to the presence of electronegative atoms. Phase transition study from DSC suggested that the incorporation of ILs has stabilized the framework of UiO-66 by shifting the endothermic peak to a higher state. These findings were further elaborated with DFT calculation. Geometrical optimizations confirmed the structural parameter changes of UiO-66 when loaded with ILs. These was mainly contributed by the non-covalent interactions which was confirmed by the reduced density gradient scattered plot. Another important findings are the strength of hydrogen bonding at the host-guest interface was influenced by the alkyl chain length. The molecular orbital analysis also shows that the size of alkyl chain influence the reactivity of the hybrid material. The present study provides fundamental insights on the molecular interaction of UiO-66 and ILs as a hybrid material, which can open new possibilities for advanced material for metal-organic framework applications in energy storage system, catalysis, gas storage and medicinal chemistry.

Effect of thiophene rings rigidity on dye-sensitized solar cell performance. Dithienothiophene versus terthiophene as π- donor moiety

Solar cells are fabricated based on two new dyes. Dye acts as an additive to thin layer interface. The effect of the π -conjugated rigidity of the thiophene rings on the photovoltaic characteristics has been investigated. The structures of the dye 1 was based on dithieno [3,2-b:2',3'-d] thiophene-2-cyanoacrylic acid, while dye 2 was based on [2,2':5',2″-terthiophene]-5-cyanoacrylic acid and were confirmed by elemental analysis, mass spectrometry, 1H NMR and 13C NMR spectral data. The P3HT/dye 1/nc-TiO2 solar cell produced the highest efficiency of 0.3 % with an open circuit voltage of 0.7 V compared to dye 2 solar cell. This has been attributed to the difference in energy levels of the dyes and location of their HOMO relative to conduction and valence bands of nc-TiO2. The dye 1 has rigid fused thiophene rings and its HOMO is located between valence band of TiO2 and HOMO of P3HT which leads to improve the charge carrier separation and increase the current density to reach 1.2 mA/cm2.

Different reaction mechanisms of SO4•- and •OH with organic compound interpreted at molecular orbital level in Co(II)/peroxymonosulfate catalytic activation system

Hydroxyl radical (•OH) and sulfate radical (SO₄•^-) produced in advanced oxidation processes (AOPs) have been widely studied for organic contaminants degradation, however, the different radical characteristics and reaction mechanisms on organics degradation are still needed. In this study, a homogeneous Co(II)/peroxymonosulfate activation system was established for caffeine (CAF) degradation, and pH was controlled to regulate the radicals production. The different attack routes driven by SO₄•^- and •OH were deeply explored by transformation products (TPs) identification and theoretical calculations. Specifically, a method on dynamic electronic structure analysis of reactants (R), transition state (TS) and intermediates (IMs) during reaction was proposed, which was applied to elucidate the underlying mechanism of CAF oxidation by •OH and SO₄•^- at the molecular orbital level. In total, SO₄•^- is kinetically more likely to attack CAF than •OH due to its higher oxidation potential and electrophilicity index. Single electron transfer reaction (SET) is only favorable for SO₄•^-due to its higher electron affinity than •OH, while only •OH can react with CAF via hydrogen atom abstraction (HAA) route. Radical adduct formation (RAF) is the most favorable route for both •OH and SO₄•^- attack according to both kinetics and thermodynamics results. These findings can significantly promote the understanding on the degradation mechanism of organic pollutants driven by •OH and SO₄•^- in AOPs.

Upon DFT-D3 dispersion correction and ECD spectral confirmation, only several conformers can stably coexist for three fungal cycloaspeptides (A, D, G)

Dispersion correction in theoretical determination of cyclopeptide conformations is emphasized. Whether in gas approximation or in solvation simulation, the density functional theory with London dispersion correction (DFT-D3) demonstrates that only 2-3 conformers can stably coexist for cycloaspeptides (A, D, G) at B3LYP-D3 and CAM-B3LYP-D3. Conformational rationality is confirmed by electronic circular dichroism (ECD). Whether for Cotton effect or for excitation energy, TD-B3LYP-D3 has better performances than TD-CAM-B3LYP-D3 because the former can better reproduce the experiment. A molecular orbital analysis is used to interpret ECD, where two energy bands observed in experiment originates from the ππ* transitions other than the σπ* transitions. Long-range correction and solvent effect make H-bonds shorten, and dispersion correction makes them further shorten.

Microsolvated Ion-Molecule SN2 Reactions with Dual Nucleophiles Induced by Solvent Molecules

Singly-hydrated HOO - anion was found to induce alternative nucleophile HO - via proton transfer from water molecule as react with CH 3 Cl recently. To investigate the generality of this effect, the competition between the solvent-induced HO - -S N 2 pathway and the normal HOO - -S N 2 pathway is studied for the microsolvated HOO - (H 2 O) n=1,2,3 + CH 3 X (X = F, Cl, Br, I) reaction by quantum chemistry calculation. Incremental hydration increases the barrier heights of both pathways and enlarges the barrier difference between them, which favors the HOO - -S N 2 pathway. Interestingly, the barrier difference is insensitive to the leaving group. Calculation shows the water induced HO - -S N 2 pathway is highly suppressed as the degree of hydration increases beyond two. The differential barrier under incremental hydration can be explained by solvent molecules stabilizing the HOMO level of HO - (HOOH)(H 2 O) n-1 nucleophile more than that of HOO - (H 2 O) n nucleophile. Comparison between these HO - -nucleophiles and HOO - -nucleophiles suggests that α-effect exists. Activation strain analysis attributes the barrier differences to the stronger distortion of the TS of HO - -S N 2 pathway than the counterparts of HOO - -S N 2 pathway. This work adds our understanding of the role of individual solvent molecules to induce new nucleophiles of the fundamental organic reaction.

Electronic investigation of the effect of substituents on the SOD mimic activity of copper (II) complexes with 8-hydroxyquinoline-derived ligands

Density functional theory (DFT) calculations were used to study the superoxide dismutase (SOD) mimic activity of two Cu²⁺ complexes with ligands derived from 8-hydroxyquinoline (8-HQ). Electron-donating and -withdrawing substituent groups were inserted into the structures to verify changes in the reactivity. The theoretical parameters obtained were compared and validated with the experimental data available. The results showed that the reduction process occurs with greater participation of the 8-HQ ligand and the oxidation step occurs with participation of the copper atom in the complexes, where the electron received during the reduction step is used to reduce the Cu²⁺ to Cu⁺. The calculated electronic affinity showed good correlation with the experimental mimetic activity, and the analysis of this property, of total charge and of molecular orbitals indicated an increase in the mimetic activity with the insertion of electron-withdrawing substituent groups in the structures.

Bis(acetylacetonato)copper(II) - structural and electronic data of the neutral, oxidized and reduced forms

Bis(acetylacetonato)copper(II) can be synthesized economically and with ease by the reaction between acetylacetone and a copper salt (Cu(OAc)₂ or CuCl₂·2H₂O). When used as catalyst, bis(acetylacetonato)copper(II) is sometimes being oxidized to Cu(III) or reduced to Cu(I), although only the structure of the neutral form is known experimentally. The content of this paper provides computational chemistry calculated data of the geometry, electronic structure, spin state and frontier orbitals for the neutral, as well as the oxidized and reduced forms of the bis(acetylacetonato)copper(II) molecule. This data shows that both the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) of the neutral molecule are copper based. The neutral molecule is a spin = ½ system. The data shows that the spin state of both the oxidized and reduced molecules is zero.

Optical activities of steroid ketones - Elucidation of the octant rule

Theoretical calculations of optical activities in steroid ketones are presented by using modern semi-empirical PM7 wavefunctions. Both circular dichroism (CD) and specific rotation, which is proportional to optical rotation dispersion (ORD), are well simulated, and signs of the Cotton effect at the most long-wavelength region are fully in accordance with the experimental results. The good accordance is related to the octant rule, which is deduced within the framework of the perturbation theory. Our treatment is promising to predict the signs of the Cotton effect of large molecules, and thus, the absolute configurations can also be grasped without demanding procedures.

Ab initio scrutiny of endohedral C20 fullerenes implanted in between gold electrodes

Using the smallest non-classical fullerene, we investigate the impact of endohedral fullerene molecules on the quantum transport through molecular junctions, and then compared this with the pure C₂₀-based molecular junction. By employing the density functional theory combined with the non-equilibrium Green's function, we contemplated different electronic parameters, namely, density of states, transmission coefficient, energy levels, molecular orbitals, conduction gaps, electron density and their charge transfer. A knowledge of these physical parameters is necessary in order to calculate current and conductance computed using Landauer-Büttiker formalism. The molecule-electrode coupling influenced by endohedral molecules affects junction devices in a unique manner. We observe that the highest quantum transport is possible in an Au-N@C₂₀-Au and Au-O@C₂₀-Au junction device, and is even higher than that of the intrinsic C₂₀ fullerene junction. Another notable observation is that the F@C₂₀ molecule exhibits the least conducting nature, being even lower than that of the endohedral molecule formed by inserting the noble element, neon. Graphical abstract Electrical characteristics of Endohedral fullerene junctions.

UV direct photolysis of sulfamethoxazole and ibuprofen: An experimental and modelling study

Photodegradation characteristics of pharmaceuticals and personal care products (PPCPs) during UV irradiation are of practical and scientific importance in selecting operational parameters during water treatment processes. In this study, the molar extinction coefficient (ε), quantum yield (φ), and degradation kinetics of neutral/anionic forms of sulfamethoxazole (SMX) and ibuprofen (IBU) were compared by varying solution pH. The degradation kinetics of the target compounds were observed to reversely correlate to the energy gap between highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) values of the target compounds. Then, a kinetic model for predicting the direct photolytic rates at different solution pH was established based on ε and φ of neutral/anionic species. The root mean squared errors for the modeled values suggest that the model exhibits good predictive power. Finally, in order to evaluate the electrical energy consumption during the UV direct photolysis process, the electrical energy per order (EE/O) was assessed. The experimental and modelling results are important to elucidate the mechanism of degradation of target PPCPs under UV irradiation and allow for the selection of optimal conditions in water treatment processes.

Photophysics of a coumarin based Schiff base in solvents of varying polarities

The present work reports detailed photophysics of a coumarin based Schiff base, namely, (E)-7-(((8-hydroxyquinolin-2-yl)methylene)amino)-4-methyl-2H-chromen-2-one (HMC) in different solvents of varying polarity exploiting steady state absorption, fluorescence and time resolved fluorescence spectroscopy. The dominant photophysical features of HMC are discussed in terms of emission from an intramolecular charge transfer (ICT) excited state. Molecular orbital (MO) diagrams as obtained from DFT based computational analysis confirms the occurrence of charge transfer from 8'-hydroxy quinoline moiety of the molecule to the coumarin part. The notable difference in the photophysical response of HMC from its analogous coumarin (C480) lies in a lower magnitude of fluorescence quantum yield of the former, particularly in the solvents of low polarity, which is rationalized by considering the higher rate of non-radiative decay of HMC in apolar solvents. Phosphorescence emission as well as phosphorescence lifetime of HMC has also been reported in 77K frozen matrix.

The DFT-NEGF scrutiny of doped fullerene junctions

Using the smallest non-classical fullerene, we investigate the impact of doping at the molecule-electrode interface on the electron transport of molecular junctions. This is accomplished by employing the density functional theory combined with the non-equilibrium Green's function. We contemplate different electronic parameters, namely, density of states, transmission coefficient, energy levels, molecular orbitals, conduction gaps, electron density, and their charge transfer. The relevance of these physical parameters is obtained to calculate their electrical parameters, current, and conductance, computed from Landauer-Büttiker formalism. The molecule-electrode coupling is influenced by the nature of doping atoms and affects the junction devices in a unique course. A particular aftermath is noticed in Au-C₁₈O₂-Au device with highest ballistic transport despite the electro-negative nature of oxygen atoms. Moreover, an interesting feature is observed in Au-C₁₈Be₂-Au device with double-barrier transmission resonance and corresponding oscillating conductance. Graphical abstract The doped C₂₀ fullerene in molecular and device mode.

On the structural and electronic properties of hexanuclear vanadium oxide clusters V6On(-/0) (n=12-15): is V6O12 cluster planar or cage-like?

Density functional theory (DFT) calculations are carried out to investigate the structural and electronic properties of a series of hexanuclear vanadium oxide clusters V6On(-/0) (n=12-15). Generalized Koopmans' theorem is applied to predict the vertical detachment energies (VDEs) and simulate the photoelectron spectra (PES) for V6On(-) (n=12-15) clusters. Extensive DFT calculations are performed in search of the lowest-energy structures for both the anions and neutrals. All of these clusters appear to prefer the polyhedral cage structures, in contrast to the planar star-like structures observed in prior model surface studies for the V6O12 cluster. Molecular orbitals are performed to analyze the chemical bonding in the hexanuclear vanadium oxide clusters and provide insights into the sequential oxidation of V6On(-) (n=12-15) clusters. The V6On(-) (n=12-15) clusters possess well-defined V(5+) and V(3+) sites, and may serve as molecular models for surface defects. Electron spin density analyses show that the unpaired electrons in V6On(-) (n=12-14) clusters are primarily localized on the V(3+) sites rather than on the V(5+) sites. The difference gas phase versus model surface structures of V6O12 hints the critical roles of cluster-substrate interactions in stabilizing the planar V6O12 cluster on model surfaces.

Structural, electronic, vibrational and NMR spectral analyses of [Ru(OAc)(2cqn)2NO] (H2cqn=2-chloro-8-quinolinol) isomers

Geometries of three [Ru(OAc)(2cqn)2NO] (H2cqn=2-chloro-8-quinolinol) isomers were fully optimized with density functional theory (DFT), and compared with their crystal structures. Their electronic spectra, infrared and NMR spectra were also calculated at the B3LYP level with Lanl2dz and 6-311G(d,p) as the basis set. And good agreement had been achieved between experimental and theoretical values of structural parameter, UV-vis absorption and scaled vibration frequency. With the gauge independent atomic orbital (GIAO) method, chemical shifts in (1)H and (13)C NMR of these isomers were also calculated, which could reasonably match with the experimental data. The calculated frontier molecular orbitals suggested that the electronic transition from a ligand-based orbital to an antibonding overlap of the Ru(d) and π(∗) NO(p) control the photo-induced reactivity of [Ru(OAc)(2cqn)2NO] complexes.