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An operationally simple protocol is described for the facile, modular and regioselective access of all-pyrano-moiety-substituted iminochromenes, particularly under undried acetonitrile and air atmosphere.

Pd-catalyzed borylation of fluorobenzene was theoretically studied. DFT calculations revealed that the reaction occurs through an unprecedented 3 + 6-membered ring transition state, in which one LiHMDS (HMDS = hexamethyldisilazane) acts as a ligand and another LiHMDS is essential to provide Li···N and Li···F interactions, overcoming the large destabilization of the strong phenyl-F bond distortion. The characteristic feature of LiHMDS was elucidated by comparing it with HMDS and NaHMDS analogues.

A redox-neutral benzylic C-O cyclization under beneficial transition-metal-free conditions is reported. Key to the success of this process is the utilization of the Tf anion as the leaving group for achieving the redox-neutral transformation. This protocol delivers a series of captivating helical compounds having various functionality in good-to-excellent yields. It is particularly noteworthy that sterically hindered helical compounds are conformationally stable. In addition to simple helical chromenes, the bihelical multiple-ring systems which are potentially useful in material chemistry are also easily attained by employing this method. DFT calculation revealed that quinone intermediate is the key species, among four possible mechanisms, for accomplishing the desired cyclization via an oxa-6π-electrocyclization pathway.

Engineering the preorganization of photoactive units remains a big challenge in solid-state photochemistry research. It is of not only theoretical importance in the construction of topochemical reactions but also technological significance in the fabrication of advanced materials. Here, a cyanostilbene derivative, (Z)-2-(3,5-bis(trifluoromethyl)phenyl)-3-(naphthalen-2-yl) acrylonitrile (BNA), was crystallized into two polymorphs under different conditions. The two crystals, BNA-α and BNA-β, have totally different intra-π-dimer and inter-π-dimer hierarchical architectures on the basis of a very simple monomer, which provides them with distinct reactivities, functions and photoresponsive properties. Firstly, two different types of solid-state [2 + 2] photocycloaddition reaction: (i) a typical olefin–olefin cycloaddition reaction within the symmetric π-dimers of BNA-α and (ii) an unusual olefin-aromatic ring cycloaddition reaction within the offset π-dimers of BNA-β have been observed, respectively. Secondly, the crystal of BNA-α can be bent to 90° without any fracture, exhibiting outstanding flexibility upon UV irradiation, while the reversible photocycloaddition/thermal cleavage process (below 100 °C) accompanied by unique fluorescence changes can be achieved in the crystal of BNA-β. Finally, micro-scale photoactuators and light-writable anti-counterfeiting materials have been successfully fabricated. This work paves a simple way to construct smart materials through a bottom-up way that is realized by manipulating hierarchical architectures in the solid state., Two crystals with different hierarchical architectures are observed based on a single molecule, achieving different types of [2 + 2] photocycloaddition. Finally, controllable photoactuators and light-writable materials are successfully fabricated.

The sluggish kinetics and unclear mechanism have significantly hindered the development of Li-CO2 batteries. Here, a Li-CO2 battery cathode catalyst based on a porphyrin-based covalent organic framework (TTCOF-Mn) with single metal sites is reported to reveal intrinsic catalytic sites of aprotic CO2 conversion from the molecular level. The battery with TTCOF-Mn exhibits a low overpotential of 1.07 V at 100 mA/g as well as excellent stability at 300 mA/g, which is one of the best Li-CO2 battery cathode catalysts to date. The unique features of TTCOF-Mn including uniform single-Mn(II)-sites, fast Li+ transfer pathways, and high electron transfer efficiency contribute to effective CO2 reduction and Li2CO3 decomposition in the Li-CO2 system. Density functional theory calculations reveal that different metalloporphyrin sites lead to different reaction pathways. The single-Mn(II) sites in TTCOF-Mn can activate CO2 and achieve an efficient four-electron CO2 conversion pathway. It is the first example to reveal the catalytic active sites and clear reaction pathways in aprotic Li-CO2 batteries.

Zn=Zn double bonded-especially double-π bonded-systems are scarce due to strong Coulomb repulsion caused by the Zn atom's internally crowded d electrons and very high energy of the virtual π orbitals in Zn2 fragments. It is also rare for Zn atoms to exhibit negative oxidation states within reported Zn-Zn bonded complexes. Herein, we report Zn=Zn double-π bonded octahedral clusters Zn2 M4 (M=Li, Na) bridged by four alkali metal ligands, in which the central Zn atom is in a negative oxidation state. Especially in D4h -Zn2 Na4 , the natural population analysis shows that the charge of the Zn atom reaches up to -0.89 |e| (-1.11 |e| for AIM charge). Although this cooperation inevitably increases the repulsion between two Zn atoms, the introduction of the s1 -type ligands results in occupation of degenerated π orbitals and the electrons being delocalized over the whole octahedral framework as well, in turn stabilizing the octahedral molecular structure. This study demonstrates that maintaining the degeneracy of the π orbitals and introducing electrons from equatorial plane are effective means to construct double-π bonds between transitional metals.

Palladium-catalyzed C–F bond arylation of pentafluorobenzene was theoretically investigated as an example of aryl–F bond functionalization. DFT computations show that C3-regioselective arylation of pentafluorobenzene occurs more favorably than C1 and C2-ones as reported experimentally, through oxidative addition of the C–F bond to Pd0 species, transmetalation and reductive elimination of the C–C bond. Oxidative addition of the C–F bond is the rate-determining and regioselectivity-determining step. The lower energy transition state of the oxidative addition of the C3–F bond (TS-C3) arises from a larger stabilization energy between Pd0(BrettPhos) and distorted pentafluorobenzene moieties in TS-C3 than those in TS-C1 and TS-C2. The larger stabilization energy is a result of a lower σ* orbital energy of the distorted C3–F bond than those of C1–F and C2–F bonds, which leads to a larger charge transfer from the Pd dπ orbital to the σ* orbital of the C3–F bond. The results suggest that both σ* orbital energy and bond dissociation energy are important factors for determining the reactivity of the C–F bond. Also, the activation barriers of the C–F bond with different substitution groups follow the order: NO2 < COOMe < CN ∼ CF3 < F, which is approximately consistent with the order of electron-withdrawing ability of these groups. It is theoretically predicted here that NMe2-substituted BrettPhos is better for C–F bond cleavage than BrettPhos, where three NMe2 groups are introduced to BrettPhos instead of the isopropyl groups.

The C–N cross-coupling reaction has been achieved by photoredox-mediated iridium/nickel dual catalysis, but its mechanism is still controversial in these reactions. A theoretical mechanistic study of the highly chemoselective C–N cross-coupling of pyrrolidine with 4-bromobenzotrifluoride has been performed using density functional theory (DFT) calculations. The oxidation state modulation mechanisms initiated by reductive quenching and oxidative quenching are unfavourable due to the mismatched redox potentials and slow electron transfer rates. In contrast, a radical mechanism merging reductive quenching (IrIII–*IrIII–IrII–IrIII) and nickel catalytic cycles (NiII–NiIII–NiII–NiII) is favourable. It consists of four major processes: exogenous base triggered successive single electron transfer (SET) and hydrogen atom transfer (HAT) to generate a nitrogen-centred radical, radical capture by nickel(II) dibromide, SET to regenerate iridium(III), and the rate-determining σ-bond metathesis to achieve the C–N cross-coupling. Furthermore, the suppression effect caused by α-substitution of pyrrolidine on the reaction is dominantly attributed to the steric effect rather than the electronic effect. Unlike the C–N cross-coupling, the concerted σ-bond metathesis involving nickel(II) is inapplicable for the C–O and C–S cross-couplings due to the high energy barriers. This study is expected to provide new mechanistic insights into metallaphotoredox-catalysed C–N cross-coupling.

The nature of the 2e/12c bond and its conversion to a carbon-carbon single bond in phenalenyl dimers have prompted a great deal of interests recently. In this work, we theoretically investigated a series of π-stacking phenalenyl derivatives with 2e/12c bonding character by density functional theory (DFT) calculations to elucidate origin of this unusual bond conversion. Results show that bond-conversion of the phenalenyl dimer easily occurs at room-temperature both dynamically and thermodynamically. However, bond-conversion of hetero π-stacking adducts, in which the two center carbon atoms were substituted by boron and nitrogen atoms, respectively, is much more difficult, because the 2e/12c bond is stabilized by its charge transfer character. Consequently, the bond-conversion is an endothermic process, albeit with a low conversion barrier. Interestingly, Lewis acid-base interactions would be induced by substitution of the center nitrogen atom to phosphorus atom. The 2e/12c bond is further stabilized by 5.9 kcal mol-1 and its conversion is also thermodynamically unfavorable.

Iridium-catalyzed C–H borylation of THF was theoretically investigated as example of sp3 C–H functionalization. DFT computations show that β-regioselective borylation occurs more easily than does α-regioselective, as reported experimentally, through oxidative addition of C–H bond to iridium(III) species and reductive elimination of B–C bond. The reductive elimination is both a rate-determining step and a regioselectivity-determining step. The lower energy transition state (TS) of the reductive elimination of β-boryloxolane arises from the Ir···(β-oxolanyl) interaction at TS being stronger than the Ir···(α-oxolanyl) one. The Ir···(β-oxolanyl) interaction being stronger than the Ir···(α-oxolanyl) one is a result of the valence orbital energy of the α-oxolanyl group being higher than that of the β-oxolanyl group due to antibonding overlap of the valence orbital with O 2p orbital, where SOMO of oxolanyl radical is taken as valence orbital hereinafter. Reactivity of substrate decreases following the order prim...

Methane borylation catalyzed by Cp*M(Bpin)n (M = Ru or Rh; HBpin = pinacolborane; n = 2 or 3) and (TMPhen)Ir(Bpin)3 (TMPhen = 3,4,7,8-tetramethyl-1,10-phenanthroline) was investigated by DFT in com...

The efficient regioselective C-H cyanoalkoxylation and cyanoalkylation of 8-aminoquinoline derivatives at the C5 position have been achieved under O2 and N2 atmospheres, respectively. Using 2,2'-azobisisobutyronitrile (AIBN) as a radical precursor, the protocols afforded the corresponding products in moderate to good yields with broad substrate generality through Cu(OAc)2 or NiSO4 catalysis. Furthermore, the single electron transfer (SET) mechanism was proposed via a radical coupling pathway.

Herein, we presented a series of Be2X4Y2 clusters (X = Li, Na and Y = Li, Na, K) containing Be[triple bond, length as m-dash]Be triple bonds, which were constructed by six alkali metals as electron-donating ligands. By virtue of the electrostatic potential mapping of the precedent Be[double bond, length as m-dash]Be double-π bonded D4h-Be2X4 clusters, the Be2X4Y2trans-bent geometries and the Be[triple bond, length as m-dash]Be triple bonds inside were both well interpreted. More remarkably, we first identified a perfect classical Be[triple bond, length as m-dash]Be triple bond in D4h-Be2Na4K2 and its Wiberg bond index of Be-Be (WBIBe-Be) reached up to 2.43. Meanwhile, our strategy provides a new approach to explain the trans-bent structure caused by terminal coordination.

N-Heterocyclic carbene (NHC) ligands effective for the cross-coupling of nitroarenes were identified. A rational design of the NHC ligand structures enabled significant reduction of catalyst loadings compared with the previous system employing BrettPhos as a phosphine ligand. Experimental and theoretical studies to compare these ligands gave some insights into high activity of the newly developed NHC ligands.

An external electric field (EEF), as a metal-free catalyst, catalyzing the Markovnikov hydrosilylation of styrene was studied for the first time. As compared to the field-free situation, the barrier height was almost halved upon the application of EEF with a field strength of 180 × 10−4 a.u. in the direction perpendicular to the “bond axis”. Therefore, the use of EEF not only resolved the questions of the separation of homogeneous catalysts from the reaction mixture, but also facilitated the reaction by decreasing its barriers. Furthermore, we found that the lower the energy of the transition state (TSX) and the higher the energy of the HOMO of the reactant (R1′), the lower the barrier height of hydrosilylation. Hopefully, this study can provide guidance toward experiments involving an external electric field.

Pd0(BrettPhos) (1) was experimentally applied to Suzuki–Miyaura reactions of nitroarenes which occur through oxidative addition of nitroarene (ArNO2) to Pd0. On the other hand, Pd0(tBu-BrettPhos) (2) was experimentally applied to nitrations of bromoarenes which occur through reductive elimination of nitroarene. DFT calculations disclosed that oxidative addition of 4-nitroanisole to 1 was exergonic but that to 2 was endergonic, indicating that 1 is useful for oxidative addition of an Ar–NO2 bond but 2 is useful for reductive elimination of an Ar–NO2 bond. This difference in reactivity between 1 and 2 is explained in that bulky tBu groups on tBu-BrettPhos destabilize the PdII complex PdII(Ar)(NO2)(tBu-BrettPhos) due to large steric repulsion between Ar and tBu-BrettPhos but less bulky cyclohexyl groups on BrettPhos do not. It is theoretically predicted here that NMe2-substituted BrettPhos is better for Ar–NO2 bond cleavage than BrettPhos but xyl-BrettPhos is good for Ar–NO2 formation, as is tBu-BrettPhos, w...

The strong adsorption stability and significantly improved incident photon-to-current conversion efficiency (IPCE) of the new anchoring group hydantoin moiety (HY) introduced into D-A-π-A dyes for dye sensitized solar cells (DSSCs), compared with the commonly used anchoring group cyanoacrylic acid (CA), were investigated through DFT/TD-DFT calculations on the dye@(TiO2)48 interfacial electron dynamics for the first time. It is found that the dissociative bidentate bridging mode with a hydrogen bond is the most stable adsorption configuration on the TiO2 anatase (101) surface for HY-based dyes and could produce a dramatic increase in adsorption energy compared with that of CA-based dye. Energy decomposition analysis (EDA) was performed to elucidate the different adsorption energies for the different anchoring groups with different adsorption configurations. A simplified Tamm-Dancoff density functional theory approach (sTDA-DFT), proposed by Grimme, was used to calculate the excitation energy and oscillator strength of the sensitizers after adsorption. The calculated results indicate that the adsorption mode has significant effects on the absorption spectrum. In contrast to CA-based dye, HY-based dye exhibits comparable light harvesting ability after adsorption due to the combined effects of different adsorption configurations, although the isolated dye exhibits a blue-shifted absorption spectrum. It shows a similar electron injection and dye regeneration driving force, but the significantly larger coupling between the sensitizer and the semiconductor for HY-based dye is the main reason for its improved IPCE. Moreover, to further improve the light-harvesting ability of the dyes, two other heterocyclic groups, rhodanine (RD) and 2-(3-oxo-2,3-dihydroinden-1-ylidene)-malononitrile (MT), were introduced into the dyes as anchoring groups. The results show that dyes with the RD anchoring group exhibited significantly enhanced light harvesting ability with the red-shifted absorption spectrum, higher electron injection efficiency with larger electronic coupling and strong adsorption ability; thus, it is worthy of experimental synthesis for use in high-performance dye sensitized solar cells.

Based on s-indaceno[1,2,3-cd;5,6,7-c′d′]diphenalene (1) consisting of two phenalenyl moieties, the monomer 2 and its dimer 22 are designed by boron and nitrogen atoms substituting the central carbon atoms of phenalenyl moieties. Calculated energy decompose analysis (EDA) shows that the orbital interaction for 22 possesses a large attractive contribution of −18.31 kcal mol–1, which is dominated by the π–π stacking interaction between the upper and the lower π-conjugated units. Interestingly, the natural population analysis (NPA) charge and the transition density matrix (TDM) show that both intramolecular charge transfer and intermolecular charge transfer (CT) exist in 22. Further, the first hyperpolarizability (βtot = 4.56 × 104 au) of 2 with intramolecular CT is greatly larger than that of reported molecule 3 (5.45 × 103 au) with intermolecular CT. Significantly, 22 exhibits the largest βtot value to be 1.42 × 105 au, which is caused by combining the intra- and intermolecular CT transitions (βx = 1.40 × 1...

For novel all-metal electride, multicage chain structures [(Ni@Ge9) Ca3]n (n = 1–4) with all real frequencies are obtained theoretically for the first time. In the structure of n = 1, the Ni@Ge9 metal cage as the shortest chain skeleton is surrounded by nonbridge Ca atoms. In the structures of n = 2–4, Ni@Ge9 metal cages are connected by bridge Ca atom pair(s) forming new hybrid multicage chain skeletons surrounded by nonbridge Ca atoms. And interesting pull–push electron relay occurs. The chain skeleton pulls valence electrons from nonbridge Ca atoms forming skeleton polyanion, and then formed polyanion pushes remaining valence electrons of the Ca atoms forming excess electrons. The excess electron numbers are Ne = 2, 0, 4, 4 for n = 1, 2, 3, 4, respectively. It is shown that these structures with excess electrons are molecular all-metal electride multicage chains, unexpectedly, and the structure (n = 2) without excess electron is a Ca salt. For nonlinear optical (NLO) response, the electride chains have...

Recently, the structure-property relationships of an attractive isomeric radical 1 (Phys. Chem. Chem. Phys., 2016, 18, 29041–29044) with famous phenalenyl (PLY) was investigated. Can PLY and 1 form stable π-dimers? The single point energy scan result shows that the staggered π-dimer (2) has the lowest energy. In order to explore intermolecular charge-transfer and nonlinear optical property, two π-dimers (2a and 2b by boron and nitrogen atoms substituting the central carbon atoms of 2) are designed. 2 has smaller intermolecular charge-transfer (0.020) and the first hyperpolarizability (βtot, 3.18 × 102 au). However, boron and nitrogen substitution effect can greatly enhance intermolecular charge-transfer (0.215 for 2a and 0.181 for 2b) and the βtot values (6.32 × 103 for 2a and 6.80 × 103 for 2b). Interestingly, the βtot values of 2a and 2b are close to each other, but their βz components and the NBO charge analysis show that 2a and 2b have opposite direction of charge transfer, which can be well explained by the difference of the dipole moment component (Δμz) between the ground and the excited states. Further, the first hyperpolarizability density study clearly substantiates the difference in their βzzz values: negative contribution for 2a is much larger than positive contribution, while the first hyperpolarizability density for 2b shows much larger positive contribution. Thus, the primary component of βzzz is negative value for 2a and βzzz is positive value for 2b. Combining with the frontier molecular orbital (FMO) and the electron density difference map (EDDM), intermolecular charge-transfer transition from B substituted fragment to N substituted fragment for 2a and 2b is concluded. The significant structure-property relationships in present π-dimers are beneficial for further theoretical and experimental investigations of high-performance nonlinear optical materials.

Synthesis of biaryls via the Suzuki–Miyaura coupling (SMC) reaction using nitroarenes as an electrophilic coupling partners is described. Mechanistic studies have revealed that the catalytic cycle of this reaction is initiated by the cleavage of the aryl–nitro (Ar–NO2) bond by palladium, which represents an unprecedented elemental reaction.

Phenalenyl π-dimer (PLY2) has recently attracted intensive research interest due to its unique structure and binding characteristics (two-electron/12-center bonding). The directional transfer of electron or electron pair under the external electric field can produce a new structure with interesting properties. In the present work, we investigate for the first time the effect of the external electric field along the main molecule axis on PLY2. Two unpaired electrons between two layers are gradually shifted to the upper layer with increasing of the external electric field strength (Fext): the weaker the two-electron/12-center bonding, the stronger the electrostatic interaction between two layers. Significantly, a small increment of Fext makes a big difference: the interlayer distance in the PLY2 is sharply elongated from 3.241 A (Fext = 203 × 10–4 au) to 3.485 A (Fext = 204 × 10–4 au), which leads to the two-electron/12-center bonding breaking at 204 × 10–4 au. Therefore, the Fext = 204 × 10–4 au is regarde...

In the present study, DFT calculations are carried out on domestically designed 7-methyl-2-phenyl-5’H-spiro[chromene-4,2′-chromeno[3,4-e][1,3]oxazin]-5′-one spiropyran and merocyanine derivatives to recognize alkali and alkaline earth metal ions. Detection of these metal ions can be attained by exploiting the variation of the second-order nonlinear optical properties. Merocyanine forms of these derivatives exhibit the ability to complex with different metal ions (Li+, Na+, K+, and Ca2+), which is associated with large contrasts in the hyper-Rayleigh scattering (HRS) response as a function of metal size and charge. Interestingly, in this study, Mero-Li+ shows significant nonlinear optical response with dynamic HRS first hyperpolarizability amounting to 7607 a.u., which is about nine times higher than its corresponding spiro form (846 a.u.) at the CAM-B3LYP/6-311G* level of theory. The present investigation clarifies the effect of metal nature on the enhancement of the first hyperpolarizability between the closed and open forms of the studied coumarin derivatives.

Iridium-catalyzed C-H borylation of THF was theoretically investigated as example of sp

In this work, by combining the superiority of polyoxometalates (POMs) and catalytic single-metal site Co of metalloporphyrin, a series of mixed-valence POM-based metal-organic frameworks (MOFs) composites is synthesized by a post-modification method. The electron-transfer property of POM@PCN-222(Co) composite is significantly enhanced owing to the directional electron-transfer from POM to single-metal site Co in PCN-222(Co). In particular, H-POM@PCN-222(Co) gives a high Faradaic efficiency of 96.2% for electroreduction of CO2 into CO and good stability over 10 h. DFT calculations confirm that the directional electron transfer, which accelerates the multi-electron transfer from the electrode to active single-metal site Co, enriches the electron density of the Co center, and ultimately reduces the energy of the rate-determining step, thus increasing the catalytic activity of CO2 reduction reaction (CO2 RR). This work therefore suggests some new insight for the design of efficient electrocatalysts for CO2 RR.

For a photochromic spiro-diarylethene derivative (Spiro-DAE), its photocyclization reaction and multicolour fluorescence modulation performances were investigated based on a series of density functionals calculations in this work. Some elementary properties such as geometric and electronic structures at ground and the first excited state (S1), absorption and emission spectra in respective open-ring and closed-ring structures were compared, which indicate the cyclization reaction may occur at S1. It is further verified by the lower activation barrier (3.4 kcal/mol) of the transition state at S1 potential energy surface. The photochromic reaction rates for both cyclization and cycloreversion processes were quantitatively estimated, which suggests the much smaller radiative and internal conversion rates contribute to the higher photocyclization rate and thus efficiency. Furthermore, we suspect that the dihydroacridine fragment may make important contribution to the cyclization reaction occurring at S1 considering its contribution to electronic structure.

In this study, density functional theory (DFT) and time-dependent density functional theory (TDDFT) calculations were employed to investigate the geometries, electronic structures, reorganization energy (λ) and photophysical properties of four cyclometalated Pt(II) complexes (bzq)Pt(dpm) (1), (bzq)Pt(ppy) (2), (bzq)Pt(Ncaz) (3) and (bzq)Pt(Ndbt) (4) (where bzq = benzo[h]quinoline, dpm = dipivolylmethanoate, ppy = 2-phenylpyridine, Ncaz = N-substituted carbazole and Ndbt = N-substituted dibenzothiophene). In addition, the radiative decay processes and zero-field splitting were calculated based on the spin–orbit coupling (SOC) effect, and nonradiative decay pathways were discussed to evaluate the phosphorescence efficiency qualitatively. All the complexes retain the bzq as a cyclometalated ligand and our research focuses on the role recognition of another ancillary ligand modification theoretically. According to the results, in complexes 2–4 replacing the dpm with different ligands shows better rigidity which may weaken the nonradiative decay pathways and enhance the capability of charge transfer. Furthermore, complexes 1–4 tend to be bluish-green luminescent materials, and the emission wavelengths of 1, 2 and 4 are close to each other due to the similar excited state energy levels and electronic density distribution. Compared with complex 1, the radiative decay rate constants (kr) of 2–4 are greatly increased. Therefore, the designed complexes would be potential phosphorescence materials because of their high phosphorescence quantum efficiency and complex 3 can also serve as a promising bipolar transporting material due to its better charge transfer balance character.

The size-selective formation of eight molecular recognition pairs between the host corannulene and fullerene guest of various size have been studied by taking advantage of concave–convex π–π interactions. Herein, the structures, binding interactions, electronic absorption spectra, and first hyperpolarizabilities have been explored using density functional theory calculations. It is found that with the aim to maximize the concave–convex shape complementarity, the base of fullerene can be modified at certain angles with the central ring plane of C20H10 (0° for complexes 1–4 and 46°, 34°, 19°, and 5° for complexes 5–8, respectively). The interaction energies depend linearly on the convex surface area and the size of the fullerene sphere. Further, the results of first hyperpolarizabilities show that the shape of the fullerene is the dominant factor for complexes 1–4 because of the intramolecular charge transfer (CT) within fullerene cage. Among them, complex 4 presents the largest βtot value as 5.64 × 10–30 e...

A series of Li@BCN models were systematically investigated to explore the physical origin of the interaction between lithium atoms and BCNs. Theoretical results show that the crucial electron population in the BCNs of Li@B-BCN and Li@N-BCN series is dramatically different. As results, the first hyperpolarizability of Li@B-BCN series increases with the increase of carbon proportion whereas that of Li@N-BCN series significantly decreases with the increase of carbon proportion. The results indicate that the physical properties of Li@BCN models are significantly dependent on the different chemical environment of the tube termination.

The special iron(II) polypyridyl complex substituted by fluorine ([Fe(dftpy)2]2+, dftpy = 6,6″-difluoro-2,2’; 6′2″-terpyridine) with uncommon mixed ground states has been detected recently, but the related explanation and characterization are not enough, especially for the influence of substituents. On the basis of previous studies, the key problem of mixed spin states is expected to be described very well by means of theoretical calculations. In this work, density functional theory (DFT) and time-dependent density functional theory (TDDFT) calculations have been carried out to study the characteristics of the excited states in detail. Comparing with the parent complex [Fe(tpy)2]2+ (tpy = 2,2′:6′,2″-terpyridine) and corresponding bromine or chlorine substituted derivates, the ground states of [Fe(dftpy)2]2+ stay around the mixture of singlet state and quintet state, but also there is rare high spin excited state lifetime. Among the halogen substituted complexes, [Fe(dftpy)2]2+ has the shortest MLCT state lifetime of 14.0 ps which has been much longer than subpicosecond lifetime of [Fe(tpy)2]2+. The reason is explored by the combination of electronic structures, absorption properties, extended transition state coupled with natural orbitals for chemical valence (ETS-NOCV) and potential energy curves (PECs). We can find that the bond lengths of Fe-Nt play a significant role on the change of metal centered (MC) ground states. With Fe-Nt extended by fluorine atoms, the quintet state becomes lower than the singlet state. Due to the deformation of structures, the interactions between metal and ligands diminish and give rise to weaker d orbital splitting than that of [Fe(tpy)2]2+, but slightly impact the pairwise orbital deformation density characteristics. And the PEC of 5MC intersects with 1,3MC which renders faster non-radiative deactivation through low-lying energy crossing points.

The present work describes the comparison of the abilities of graphene-cyclodextrin conjugates to enhance the electrochemical performance of four tyramine-related compounds. First, cyclodextrin (CD)-modified graphene conjugates were synthesized via the amine-epoxy reaction between graphene oxide (GO) and 6-deoxy-6-ethylenediamino-β-CD, followed by l -ascorbic acid reduction. The resulting conjugates were characterized using UV–vis spectroscopy, Fourier-transform infrared spectroscopy (FTIR), Raman spectroscopy, thermogravimetric analysis (TGA), X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Subsequently, for the comparative study, glass carbon electrode electrochemical sensors modified with these conjugates were prepared to detect four structurally similar analytes (tyramine, l -tyrosine, dopamine and levodopa). The sensor sensitivities of the modified electrodes were markedly higher than that of the bare electrode. Based on the results of the comparative study, several crucial factors for improving the performance of the electrodes were proposed, including the binding affinity and the binding orientation of CD toward analytes. The conclusions drawn in this study could provide theoretical foundation for the design and optimization of versatile electrochemical platforms with excellent properties.

Stable phenalenyl (PLY) radical π-dimers still play an important role for new multifunctional materials owing to their intriguing molecular structure and unusual pancake π-π bonding mode. Herein, we design a new biphenalenyl biradicaloid (1) consisting of two PLYs and one benzene ring linkage tethered by single bonds, which presents an open-shell character. Further, three π-dimers (a1, b1, and c1) combined with 1 and conventional biphenalenyl biradicaloid (a, b, and c), which are capable of forming two staggered PLY dimers, exhibiting a short interlayer distance between the monomers. Interestingly, the analysis of the frontier molecular orbital reveals that two bonding orbitals, namely, the two highest occupied molecular orbitals (HOMO and HOMO-1) are doubly occupied. The results reveal that three π-dimers display two parallel pancake bonds. Moreover, they have small diradical and tetraradical characters, large interaction energies, and strong aromaticity, which indicate the stability of these π-dimers. The present work creates a new class of strong pancake bonding and might be utilized in devising an array of materials.

A series of diradical π-dimers 2 with interesting pancake-shaped 2e/24c π-π bonding character were designed and investigated based on the famous phenalenyl (PLY) π-dimer with 2e/12c π-π bonding character. The position of stronger interaction between two layers of radicals was found by the Wiberg bond index (WBI) maximum component. Further, the different contributions of the interaction energy were analyzed quantitatively by energy decomposition analysis (EDA). Among these new diradical π-dimers, 2180 has the smallest layer distance and the largest interaction between two layers of radicals. The unusual PLY analogues can provide new insights into the unique features of two-electron/multicenter (2e/mc) π-π bonding.

Besides the classic double bond scheme, several novel schemes have been proposed to describe the nature of the chemical bond in dicarbon, including a quadruple bond and a singlet diradical state. The results presented here show a harmony between MO and VB theories., Besides the classic double bond scheme, several novel schemes have been proposed to describe the nature of the chemical bond in dicarbon (C2), including a quadruple bond and a singlet diradical state. The results from a symmetry-broken CASSCF(8,8)/aug-cc-pVTZ study present a harmony between MO and VB theories, based on the orthogonal hybridization of the 3σg and 2σu orbitals together with the other six pristine valence orbitals. This scheme achieves the same bonding energy, RC–C, ωe and one electron density as that from the eight pristine valence orbitals. A quadruple bond scheme, identical to Prof. Shaik's result from VB theory, is achieved with the 4th bond energy in the range of 12.8–27.6 kcal mol–1. Meanwhile, the weight of a singlet open-shell configuration is the highest among all the possible configurations.

Two pillared-layer metal-organic frameworks (MOFs; PMOF-55 and NH2 -PMOF-55) based on 1,2,4-triazole and terephthalic acid (bdc)/NH2 -bdc ligands were assembled and display framework stabilities, to a certain degree, in both acid/alkaline solutions and toward water. They exhibit high CO2 uptakes and selective CO2 /N2 adsorption capacities, with CO2 /N2 selectivity in the range of 24-27, as calculated by the ideal adsorbed solution theory method. More remarkably, the site and interactions between the host network and the CO2 molecules were investigated by single-crystal X-ray diffraction, which showed that the main interaction between the CO2 molecules and PMOF-55 is due to multipoint supramolecular interactions of C-H⋅⋅⋅O, C⋅⋅⋅O, and O⋅⋅⋅O. Amino functional groups were shown to enhance the CO2 adsorption and identified as strong adsorption sites for CO2 by X-ray crystallography.

In 2003, a novel compound 2 containing the benzo-15-crown-5 moiety was synthesized and described. In the present work, we have designed two compounds 1 (benzo-12-crown-4) and 3 (benzo-18-crown-6) on the basis of compound 2. Further, nine configurations N*M (N = 1, 2 and 3; M = Li+, Na+ and K+) are designed by the compounds 1, 2 and 3 complexing alkali metal cations. Density functional calculation is performed to investigate the effect of ring size and the nature of the alkali metal cations on the interaction energy, charge transfer and nonlinear optical properties. The results indicate that the interaction energy of N*M depends on both the ring size and the nature of the alkali metal cations. Moreover, the amount of net charge transfer is related to the diameters of the alkali metal cations. In addition, the calculated nonlinear optical properties reveal that compound 2 has the largest first hyperpolarizability among the three compounds 1, 2 and 3. However, the alkali metal cations give rise to different effects on the nonlinear optical properties. Significantly, the order of the first hyperpolarizability can be explained by the transition energy and the dipole moment variation within the two-state approximation.

The photosensitive polyoxometalate (POM) [PW11O39RhCH2CO2H]5− was first introduced into the liquid crystal material through the encapsulation of dimethyldioctadecylammonium (DODA+). The theoretical calculation was performed to simulate the distribution of DODA+ around the POM anion. The surface photovoltage spectroscopy (SPS) result indicated that the hybrid exhibits the photovoltaic effect upon optical illumination and displays the character of a p-type material, which paves a new way for their potential application in the optoelectronics.

Three molecules HArF@BNNT(5,0), HArF@BNNT(6,0), and HArF@BNNT(7,0) have been formed by HArF encapsulated in boron nitride nanotubes (BNNTs) with different sizes. Due to the interaction between the HArF and the BNNTs, the HAr bond lengths are in a decrease trend, while the ArF bond lengths are in an increase trend compared with those of HArF. To investigate the nature of the interaction between H and Ar and the interaction between Ar and F, the quantum theory of “atoms in molecules” was carried out. The Laplacian (▿2ρb) values of HAr suggest that the covalent interaction plays a key role in the H-Ar interaction. For ArF, the results indicate that the Ar-F interaction has a dominant noncovalent character. Moreover, the results obtained from the ratio of the kinetic-energy density (Gb) and the potential-energy density (Vb) (−Gb/Vb) and the total energy density (Hb) are in good agreement with that of ▿2ρb values. In addition, the results of natural bond orbital charge and electron density difference between the HArF and BNNTs show that less electrons transfer away from the HArF to BNNTs with the gradual increase in the diameters of the BNNTs. © 2014 Wiley Periodicals, Inc.

Recently, the N-connecting pattern of the BN-segment has been shown as a suitable strategy to enhance the static first hyperpolarizability (β0) of carbon–boron–nitride heterojunction nanotubes (J. Phys. Chem. C 2013, 117, 10039–10044). In this work, we report a quantum chemical investigation on the lithiation effect to further reveal the mechanism of modification. Interestingly, the lithiation effect is significantly dependent on the activating segment of the heterojunction nanotubes. For lithiation on the BN-segment, the β0 (3.22 × 104 au) of Li5–BN-1a is larger than that (1.42 × 104 au) of Li5–BN-2a, which shows that the N-connecting pattern of the BN-segment linking to the C-segment is an efficient way to enhance the β0 of heterojunction nanotubes. However, for lithiation on the C-segment, the β0 (6.03 × 104 au) of Li5–BN-1b is even slightly smaller than that (6.97 × 104 au) of Li5–BN-2b. Besides, results show that activating the C-segment is a more effective strategy than activating the BN-segment for...