Theoretical Insight into the Performance of Mn^II/III-Monosubstituted Heteropolytungstates as Water Oxidation Catalysts

The performance of MnII/III-monosubstituted heteropolytungstates [MnIII(H2O)­GeW11O39]5– ([GT-MnIII-OH2]5–, where GT = GeW11O39) and [MnII(H2O)­GeW11O39]6– ([GT-MnII-OH2]6–) as water oxidation catalysts at pH 9 was explored using density functional theory calculations. The counterion effect was fully considered, in which five and six Na+ ions were included in the calculations for water oxidation catalyzed by [GT-MnIII-OH2]5– and [GT-MnII-OH2]6–, respectively. The process of water oxidation catalysis was divided into three elemental stages: (i) oxidative activation, (ii) O–O bond formation, and (iii) O2 evolution. In the oxidative activation stage, two electrons and two protons are removed from [Na5-GT-MnIII-OH2] and three electrons and two protons are removed from [Na6-GT-MnII-OH2]. Therefore, the MnIV-O• species [Na5-GT-MnIV-O•] is obtained. Two mechanisms, (i) water nucleophilic attack and (ii) oxo–oxo coupling, were demonstrated to be competitive in O–O bond formation triggered from [Na5-GT-MnIV-O•]. In the last stage, the O2 molecule could be readily evolved from the peroxo or dinuclear species and the catalyst returns to the ground state after the coordination of a water molecule(s)

Computational Study on Redox-Switchable 2D Second-Order Nonlinear Optical Properties of Push−Pull Mono-tetrathiafulvalene-Bis(Salicylaldiminato) Zn(II) Schiff Base Complexes

The redox-switchable 2D second-order nonlinear optical (NLO) property of a series of tetrathiafulvalene (TTF) derivatives has been studied based on the density functional theory (DFT) calculations. The redox-active TTF unit has been considered as a manipulative center for switching the 2D second-order NLO properties. Our DFT calculations show that introduction of the TTF unit cannot effectively enhance the second-order NLO properties relative to the reference system 1 because the nonplane embowed arrangement of the TTF unit reduces the electron donor capacity. The electronic structure analysis shows that the TTF unit acts as the oxidized center in one- and two-electron-oxidized processes for 5. A significant transformation on the structure of the TTF unit, the TTF unit changes from the embowed structure to a planar structure, has been found in the series of oxidized processes according to DFT-optimized calculations. This leads to the low excited energy and different charge transfer features of the oxidized species relative to its reduced parents, and thus enhances the static first hyperpolarizabilities. The β value of one- and two-electron-oxidized species is at least ∼15 and ∼8.6 times as large as that of its reduced parents according to our DFT calculations. Simultaneously, the oxidized process increases the contributions from the y-polarized transition, and thus improves the 2D second-order NLO property

Probing the REDOX effect of helical tetraspirobenzene on nonlinear optical properties

The helical structure is a classical framework to design high-performance organic electro-optical materials. In this work, the structure-property’s relationships of helical tetraspirobenzene (1) and its oxidation (12+) and reduction (12–) products are explored. The results show that the redox brings some distinctive changes in their geometric structure and electronic property, which regulate the first hyperpolarisability (βtot). Among these structures, the 12– has the largest βtot value of 4.2 × 104, which is greatly larger than 2.0 × 102 a.u. of. 12+. Therefore, the reduction effect is more obvious than the oxidation effect. Furthermore, the UV-Vis absorption spectrum also proves this phenomenon: the oxidation product has a new red-shifted absorption peak (571 nm) and the reduction product has two new red-shifted absorption peaks (577 and 797 nm). We hope the present work can provide theoretical guidance for the search for high-performance nonlinear optical materials by using the redox effect.</p

Heterolytic versus Homolytic: Theoretical Insight into the Ni⁰‑Catalyzed Ph–F Bond Activation

The Ni0-catalyzed borylation of fluorobenzene (PhF) was theoretically investigated. Density functional theory (DFT) calculations disclosed that the Ph–F bond activation occurred heterolytically via an unprecedented nucleophilic aromatic substitution reaction (SNAr) assisted by an sp2–sp3 diboron complex [B2nep2·(OPh)]‑Na+, which forms a Ni0-ate complex as an active species. The diboron-ate complex stabilizes the transition state of the Ph–F bond activation through three interactions, a Ni···O coordination, a Na+···F cationic dipole interaction, and a charge transfer arising from NaOPh. On the other hand, the Ph–F bond activation catalyzed by Ni0(dcpe) and Ni0(PCy3)2 complexes has also been studied to allow a comparison between the monophosphine and bisphosphine ligands. Results suggest that Ni0(PCy3)2 is less effective than Ni0(dcpe) for the concerted oxidative addition of the Ph–F bond because the Ni dπ orbital of Ni0(PCy3)2 is at a lower energy level than that of Ni0(dcpe) in the equilibrium geometry. The characteristic molecular orbital features of Ni0-catalyzed Ph–F bond activation via both the nucleophilic aromatic substitution reaction (heterolytic) and the concerted oxidative addition (homolytic) were theoretically disclosed

A Series of Three-Dimensional Lanthanide Coordination Polymers with Rutile and Unprecedented Rutile-Related Topologies

The complexes of formulas Ln(pydc)(Hpydc) (Ln = Sm (1), Eu (2), Gd (3); H2pydc = pyridine-2,5-dicarboxylic acid) and Ln(pydc)(bc)(H2O) (Ln = Sm (4), Gd (5); Hbc = benzenecarboxylic acid) have been synthesized under hydrothermal conditions and characterized by elemental analysis, IR, TG analysis, and single-crystal X-ray diffraction. Compounds 1−3 are isomorphous and crystallize in the orthorhombic system, space group Pbcn. Their final three-dimensional racemic frameworks can be considered as being constructed by helix-linked scalelike sheets. Compounds 4 and 5 are isostructural and crystallize in the monoclinic system, space group P21/c. pydc ligands bridge dinuclear lanthanide centers to form the three-dimensional frameworks featuring hexagonal channels along the a-axis that are occupied by one-end-coordinated bc ligands. From the topological point of view, the five three-dimensional nets are binodal with six- and three-connected nodes, the former of which exhibit a rutile-related (4.62)2(42·69·84) topology that is unprecedented within coordination frames, and the latter two species display a distorted rutile (4.62)2(42·610·83) topology. Furthermore, the luminescent properties of 2 were studied

Theoretical Design of Perylene Diimide Dimers with Different Linkers and Bridged Positions as Promising Non-Fullerene Acceptors for Organic Photovoltaic Cells

The intermolecular stacking and crystallization of perylene diimides (<b>PDIs</b>) has become research obstacles for small molecule acceptors (SMAs). For breaking molecular rigidity and planarity, it is an executable way to increase the distortion between two <b>PDI</b> units. A class of <b>PDI</b> dimers were designed via bridging different linkers in bay positions (1–1′ bridge) and headland positions (1–2′ bridge) to screen suitable acceptor materials for organic photovoltaic cells (OPVs). Density functional theory (DFT) and time-dependent density functional theory (TD-DFT) calculations were performed to investigate their electronic structures, open circuit voltage (<i>V</i>_OC), driving forces (Δ<i>E</i>_L‑L), and some major parameters related to the short-circuit current density (<i>J</i>_SC) such as absorption spectrum and carrier transport ability. Meanwhile, the intermolecular charge transfer (inter-CT) and charge recombination (inter-CR) rates were calculated for a further analysis on charge transfer properties at donor/acceptor (D/A) interface by employing the Marcus semiclassical model. The results manifest that the investigated 1–2′ bridged molecules possess low-lying LUMO energy levels, relatively bigger Δ<i>E</i>_L‑L, bathochromic-shifted absorption, as well as the strongest maximum absorption and more effective charge transport than 1–1′ bridged molecules. Surprisingly, compared with <b>P3HT</b>/(1–1′ bridged <b>PDI</b> dimers) interface, almost constant reorganization energy (λ), higher Gibbs free energy change of exciton dissociation (Δ<i>G</i>_CT), and considerable inter-CT/inter-CR rates ratios (<i>k</i>_inter‑CT<i>/k</i>_inter‑CR) of P3HT/(1–2′ bridged <b>PDI</b> dimers) provides further evidence for that 1–2′ bridged <b>PDI</b> dimers as acceptors might perform higher efficiency in OPV device. Moreover, constructing <b>NDT</b> and <b>DPPT</b> as bridged linkers in <b>PDI</b> dimers as “push–pull” structures may rationally expect more favorable properties as acceptors in OPVs, which might provide theoretical guideline for the design and synthesis of new organic SMAs

Reply to “Comment on ‘How the Number and Location of Lithium Atoms Affect the First Hyperpolarizability of Graphene’”

Reply to “Comment on ‘How the Number and Location of Lithium Atoms Affect the First Hyperpolarizability of Graphene’

Syntheses and Characterization of Six Coordination Polymers of Zinc(II) and Cobalt(II) with 1,3,5-Benzenetricarboxylate Anion and Bis(imidazole) Ligands

Six new coordination polymers, namely [Zn1.5(BTC)(L1)(H2O)2]·1.5H2O (1), [Zn3(BTC)2(L2)3] (2), [Zn3(BTC)2(L3)1.5(H2O)]·H2O (3), [Co6(BTC)4(L1)6(H2O)3]·9H2O (4), [Co1.5(BTC)(L2)1.5]·0.25H2O (5), and [Co4(BTC)2(L3)2(OH)2(H2O)]·4.5H2O (6), where L1 = 1,2-bis(imidazol-1-ylmethyl)benzene, L2 = 1,3-bis(imidazol-1-ylmethyl)benzene, L3 = 1,1‘-(1,4-butanediyl)bis(imidazole), and BTC = 1,3,5-benzenetricarboxylate anion, were synthesized under hydrothermal conditions. In 1−6, each of L1−L3 serves as a bidentate bridging ligand. In 1, BTC anions act as tridentate ligands, and compound 1 shows a 2D polymeric structure which consists of 2-fold interpenetrating (6, 3) networks. In compound 2, BTC anions coordinate to zinc cations as tridentate ligands to form a net with (64·82)2(86)(62·8)2 topology. In compound 3, BTC anions act as tetradentate ligands and coordinate to zinc cations to form a net with (4·62·83)2(8·102)(4·6·83·10)2 topology. In compound 5, each BTC anion coordinates to three Co cations, and the framework of 5 can be simplified as (64·82)2(62·82·102)(63)2 topology. For 4 and 6, the 2D cobalt−BTC layers are linked by bis(imidazole) ligands to form 3D frameworks. In 6, the Co centers are connected by μ3-OH and carboxylate O atoms to form two kinds of cobalt−oxygen clusters. Thermogravimetric analyses (TGA) for these compounds are discussed. The luminescent properties for 1−3 and magnetic properties for 4−6 are also discussed in detail

Computational Design of Host Materials Suitable for Green-(Deep) Blue Phosphors through Effectively Tuning the Triplet Energy While Maintaining the Ambipolar Property

We theoretically designed a series of ambipolar host materials (<b>1</b>–<b>8</b>) which incorporate phosphine oxide and carbazole groups to the two ends of diphenyl (DP)-like bridges by para- and meta-connections, respectively. Density functional theory calculations were performed to investigate the influence of altering the DP-like bridges of these molecules on electronic structures and properties, and further to predict their performances as host materials in organic light-emitting diodes. The investigated results show the highest occupied molecular orbitals (HOMOs) and lowest unoccupied molecular orbitals (LUMOs) of <b>1</b>–<b>8</b>, distributed at the phenylcarbazole and the DP-like bridge, are responsible for hole and electron injection properties, respectively. The difference in the energies of HOMOs or LUMOs for <b>1</b>–<b>8</b> may be derived from different degrees of conjugation effect and electrostatic induction with altering the DP-like bridges of <b>1</b>–<b>8</b>. The singlet states (S₁), arising from the HOMO → LUMO transition, have intramolecular charge transfer character, which determines the small and different values of S₁ energies. On the other hand, altering the DP-like bridges brings a great effect on triplet exciton distributions, and consequently different triplet energies. The different singlet/triplet energies for <b>1</b>–<b>8</b> make hosts <b>1</b>–<b>8</b> suitable for four reference guests with green/deep-blue light when scientists consider the matching of host and guest in singlet/triplet energies for efficient energy transfer