Theoretical Study of the Oxidation of Methane to Methanol by the [Cu^IICu^II(μ-O)₂Cu^III(7‑<i>N</i>‑Etppz)]¹⁺ Complex

The reactivity patterns of a series of trivalent copper complexes have been studied to gain a better understanding of the chemical reactions occurring at the active site of particulate methane monooxygenase (pMMO). In this study, hybrid density functional theory is used to study the oxidation of methane to methanol mediated by the [Cu^IICu^II(μ-O)₂Cu^III(7-<i>N</i>-Etppz)]¹⁺ complex. Reaction mechanisms in different spin states were explored. Based on the calculated free-energy profile, a mechanism is suggested for the reaction of the oxidation of methane to methanol. The first step (<b>1</b> → <b>2</b>) is a hydrogen transfer to the bridged oxygen in the Cu₂O₂ core from the methane to form a methyl radical. The second step (<b>2</b> → <b>3</b>) is the radical recombination, in which the bridged hydroxyl rotates upward and exposes the oxygen moiety toward the methyl radical to form methanol. The radical recombination step is rate-limiting, with a calculated free-energy barrier of 19.6 kcal mol^–1, which is in good agreement with the experimental value of 18.4 kcal mol^–1. The mixed valent bis­(μ-oxo)­Cu^IICu^III species in the Cu₃O₄ core is directly responsible for the C–H activation of methane

Theoretical Investigations of the Chiral Transition of α‑Amino Acid Confined in Various Sized Armchair Boron–Nitride Nanotubes

We computationally study the chiral transition process of the α-Ala molecule under confined different sizes of armchair SWBNNTs to explore the confinement effect. We find that the influence of a confinement environment (in armchair SWBNNTs) on the α-Ala molecule would lead to different reaction pathways. Meanwhile, the preferred reaction pathway is also different in various sizes of armchair SWBNNTs, and their energy barriers for the rate-limiting step decrease rapidly with the decreasing of the diameters of the nanotubes. It is obvious that significant decrease of the chiral transition energy barrier occurs compared with the isolated α-Ala molecule chirality conversion mechanism, by ∼15.6 kcal mol^–1, highlighting the improvement in the activity the enantiomers of α-Ala molecule. We concluded that the confinement environment has a significant impact at the nanoscale on the enantiomer transformation process of the chiral molecule

Unexpected Opposite Influences of Para vs Ortho Backbone Fluorination on the Photovoltaic Performance of a Wide-Bandgap Conjugated Polymer

Fluorination density and regioregularity are known factors that have high impact on the performance of organic solar cells; however, due to the limited available fluorination positions, the influence of backbone fluorination positions (such as ortho, para, and meta) has not been well studied. Here we disclose that the fluorination position on a conjugated polymer backbone may have completely opposite effects on its performance. Specifically, compared to the nonfluorinated control, Devices fabricated with the conjugated polymer based on para-fluorinated dibenzo­[<i>c</i>,<i>h</i>]­[2,6]­naphthyridine-5,11-(6<i>H</i>,12<i>H</i>)-dione (DBND) block exhibit improved power conversion efficiencies (PCEs) up to 6.55%, while devices fabricated with the conjugated polymer based on ortho-fluorinated DBND block exhibit much worse PCEs as low as 1.44%, although both polymers have similar HOMO/LUMO levels, bandgaps, and backbone torsion angles. It is found that different fluorination positions result in different dipole moments, intermolecular binding energies, and syn/anti conformer ratios, which eventually lead to the distinct phase-separation behaviors of the corresponding solar cells

Computational Investigation of Acene-Modified Zinc-Porphyrin Based Sensitizers for Dye-Sensitized Solar Cells

A series of acene-modified zinc-porphyrin dyes (benzene to pentacene, denoted as LAC-1 to LAC-5) were chosen to examine their performance as photosensitizers in dye-sensitized solar cells (DSSCs). Their structural, electronic, and optical properties were investigated at the DFT/TDDFT levels using various theoretical models (i.e., the gas phase model and the implicit/explicit solvent model). The dye@TiO₂ complex was used to investigate the dye/semiconductor interfaces using both the cluster and periodic models. After a careful examination of the dependence of the results on different theoretical approaches, some basic principles could be derived based on the theoretical investigation of structure–function relationships in isolated dyes and dye–TiO₂ assemblies. Based on these ideas, some general suggestions can be proposed for the future design of dyes for use in DSSCs. For instance, the DFT functionals used in estimating the critical parameters for DSSCs should be carefully validated. Sometimes the performances of the DFT functionals can be improved by a specific energy-shift correction to compensate for systematic errors. Benchmark calculations indicated that the best approach for depicting the reduction potentials is either the M06-2X functional combined with the formula Δ<i>E</i>_red = (<i>E</i>⁰ – <i>E</i>^–)_GS or the B3LYP functional combined with Koopman’s Theorem. The best functional for estimating the excitation energies was found to be LC-ωPBE. The impact of significant thermal fluctuations on the optoelectronic properties of dyes may also be an important consideration in the prediction of more efficient dyes for use DSSCs. In contrast to the selection of DFT functionals, both the cluster and periodic models resulted in consistent views of the dye–TiO₂ interactions, indicating that the use of either model should achieve reasonable results at least in the qualitative manner