Density functional theory study on a fluorescent chemosensor device of aza‐crown ether

Three derivatives of alkyl anthracene covalently bonded to aza‐18‐crown‐6 at the nitrogen position, anthracene(CH₂)_n, (n = 1–3) which act as an on–off fluorogenic photoswitch have been theoretically studied using a computational strategy based on density functional theory at B3LYP/6‐31 + G(d,p) method. The fully optimized geometries have been performed with real frequencies which indicate the minima states. The binding energies, enthalpies and Gibbs free energies have been calculated for aza‐18‐crown‐6 ( L ) and their metal complexes. The natural bond orbital analysis is used to explore the interaction of host–guest molecules. The absorption spectra differences between L and their metal ligands, the excitation energies and absorption wavelength for their excited states have been studied by time‐dependent density functional theory with the basis set 6‐31 + G(d,p). These fluorescent sensors and switchers based on photoinduced electron transfer mechanism have been investigated. The PET process from aza‐crown ether to fluorophore can be suppressed or completely blocked by the entry of alkali metal cations into the aza‐crown ether‐based receptor. Such a suppression of the PET process means that fluorescence intensity is enhanced. The binding selectivity studies of the aza‐crown ether part of L indicate that the presence of the alkali metal cations Li⁺, Na⁺ and K⁺ play an important role in determining the internal charge transfer and the fluorescence properties of the complexes. In addition, the solvent effect has been investigated. Copyright © 2014 John Wiley & Sons, Ltd.     

1,5‐electrocyclization versus 1,5‐proton shift in imidazolium allylides and 2‐phospha‐allylides: a DFT investigation

The competitive 1,5‐electrocyclization versus intramolecular 1,5‐proton shift in imidazolium allylides and imidazolium 2‐phosphaallylides has been investigated theoretically at the DFT (B3LYP/6‐311 + +G**//B3LYP/6‐31G**) level. 1,5‐Electrocyclization follows pericyclic mechanism and its activation barrier is lower than that for the pseudopericyclic mechanism by ～5–6 kcal mol^?1. The activation barriers for 1,5‐electrocyclization of imidazolium 2‐phosphaallylides are found to be smaller than those for their nonphosphorus analogues by ～3–5 kcal mol^?1. There appears to be a good correlation between the activation barrier for intramolecular 1,5‐proton shift and the density of the negative charge at C8, except for the ylides having fluorine substituent at this position ( 7b and 8b ). The presence of fluorine atom reduces the density of the negative charge at C8 (in 7b it becomes positively charged) and thus raises the activation barrier. The ylides 7f and 8f having CF₃ group at C8, in preference to the 1,5‐proton shift, follow an alternative route leading to different carbenes which is accompanied by the loss of HF. The carbenes Pr _{7 , 8b – e} resulting from intramolecular 1,5‐proton shift have a strong tendency to undergo intramolecular S_N2 type reaction, the activation barrier being 7–28 kcal mol^?1. Copyright © 2011 John Wiley & Sons, Ltd.     

Understanding halogen‐substituent assistance in H‐atom abstraction‐based reactions of CHCl•− with CH4 − nXn (X = H,F, Cl; n = 0–3)

The effect of halogen‐substituent on hydrogen abstraction mechanisms was studied by applying density functional theory functional calculations to the gas‐phase reactions between CHCl^?? and CH_{4 ? n}X_n (X = H, F, Cl; n = 0–3), and it is found that a heavier X substituent in the substrate results in a greater stabilization of corresponding complex, a lower activation energy, a faster H‐abstraction reaction, and greater exothermicity. However, CH₄– reaction is more reactive than CH₃F– reaction under the same condition because of dominant π‐donation from the electronegative F atom. We also explored the reactivity difference for the seven reactions in terms of factors derived from bond order, second‐order perturbative energy, and activation strain model analysis. The rate constants are evaluated over a wide temperature range of 298–1000 K by the conventional transition state theory. Copyright © 2014 John Wiley & Sons, Ltd.     

Evaluation of various DFT protocols for computing 1H and 13C chemical shifts to distinguish stereoisomers: diastereomeric 2‐, 3‐, and 4‐methylcyclohexanols as a test set

¹H and ¹³C NMR chemical shifts were measured for a set of six isomers—the cis and trans 2‐, 3‐, and 4‐methylcyclohexanols. ¹H and ¹³C NMR chemical shifts were computed at the B3LYP, WP04, WC04, and PBE1 density functional levels for the same compounds, taking into account the Boltzmann distribution among conformational isomers (chair–chair forms and hydroxyl rotamers). The experimental versus computed chemical shift values for proton and carbon were compared and evaluated (using linear correlation (r²), total absolute error (|Δδ|_T), and mean unsigned error (MUE) criteria) with respect to the relative ability of each method to distinguish between cis and trans stereoisomers for each of the three constitutional isomers. For ¹³C shift data, results from the B3LYP and PBE1 density functionals were not sufficiently accurate to distinguish all three pairs of stereoisomers, while results using the WC04 functional did do so. For ¹H shift data, each of the WP04, B3LYP, and PBE1 methods was sufficiently accurate to make the proper stereochemical distinction for each of the three pairs. Applying a linear correction to the computed data improved both the absolute accuracy and the degree of discrimination for most of the methods. The nature of the cavity definition used for continuum solvation had little effect. Overall, use of proton chemical shift data was more discriminating than use of carbon data. Copyright © 2007 John Wiley & Sons, Ltd.     

Intramolecular Diels–Alder reaction in enyne–allenes: a computational investigation and comparison with the Myers–Saito and Schmittel reactions

The reaction mechanisms as well as substituted effect and solvent effect of the enyne–allenes are investigated by Density Functional Theory (DFT) method and compared with the Myers–Saito and Schmittel reactions. The Myers–Saito reaction of non‐substituted enyne–allenes is kinetically and thermodynamically favored as compared to the Schmittel reaction; while the concerted [4 + 2] cycloaddition is only 1.32 kcal/mol higher than the C₂? C₇ cyclization and more exothermic (Δ_RE = ?69.38 kcal/mol). For R₁ = CH₃ and t‐Bu, the increasing barrier of the C₂? C₇ cyclization is higher than that for the C₂? C₆ cyclization because of the steric effect, so the increased barrier of the [4 + 2] cycloaddition is affected by such substituted electron‐releasing group. Moreover, the strong steric effect of R₁ = t‐Bu would shift the C₂? C₇ cyclization to the [4 + 2] cycloaddition. On the other hand, for R₁ = Ph, NH₂, O^?, NO₂, and CN substituents, the barrier of the C₂? C₆ cyclization would be more diminished than the C₂? C₇ cyclization due to strong mesomeric effect; the reaction path of C₂? C₇ cyclization would also shift to the [4 + 2] cycloaddition. The solvation does not lead to significant changes in the potential‐energy surface of the reaction except for the more polar surrounding solvent such as dimethyl sulfoxide (DMSO), or water. Copyright © 2009 John Wiley & Sons, Ltd.     

A combined experimental and density functional study of 1‐(arylsulfonyl)‐2‐R‐4‐chloro‐2‐butenes reactivity towards the allylic chlorine

Nucleophilic substitution and dehydrochlorination reactions of a number of the ring‐substituted 1‐(arylsulfonyl)‐2‐R‐4‐chloro‐2‐butenes are studied both experimentally and theoretically. The developed synthetic procedures are characterized by a general rapidity, cheapness, and simplicity providing moderate to high yields of 1‐arylsulfonyl 1,3‐butadienes (48–95%), 1‐(arylsulfonyl)‐2‐R‐4‐(N,N‐dialkylamino)‐2‐butenes (31–53%), 1‐(arylsulfonyl)‐2‐R‐2‐buten‐4‐ols (37–61%), and bis[4‐(arylsulfonyl)‐3‐R‐but‐2‐enyl]sulfides (40–70%). The density functional theory B3LYP/6‐311++G(2d,2p) calculations of the intermediate allylic cations in acetone revealed their high stability occurring from a resonance stabilization and hyperconjugation by the SO₂Ar group. The reactivity parameters estimated at the bond critical points of the diene/allylic moiety display a high correlation (R² > 0.97) with the Hammett (σ_p) constants. 1‐Arylsulfonyl 1,3‐butadienes are characterized by a partly broken π conjugated system, which follows from analysis of the two‐centered delocalization (δ) and localization (λ) index values. The highest occupied molecular orbital energies of 1‐arylsulfonyl 1,3‐butadienes are lower than those of 1,3‐butadiene explaining their low reactivity towards the Diels–Alder condensation. Copyright © 2015 John Wiley & Sons, Ltd.     

Mechanistic insights into N‐heterocyclic carbene (NHC)‐catalyzed N‐acylation of N‐sulfonylcarboxamides with aldehydes

In the current work, density functional theory calculations were performed to elucidate the detailed reaction mechanism for N‐heterocyclic carbene (NHC)‐catalyzed oxidative N‐acylation reaction of amides with aldehydes affording imide products. According to the calculated results, the reaction is initiated by the nucleophilic attack of NHC to aldehydes forming zwitterionic intermediate, which can then form Breslow intermediate via proton transfer. The Breslow intermediate can then be oxidized affording the oxidative intermediate, which can then go through 1,2‐addition with the deprotonated N‐sulfonylcarboxamides. Subsequently, elimination of NHC catalyst produces the final imide product. Our results reveal that the proton in N‐sulfonylcarboxamides is probably abstracted by base t‐BuOK or DPQH, and the deprotonation process is barrier‐less. Moreover, for the second step, ie, the formation of Breslow intermediate, direct proton transfer is impossible to occur. On the contrary, the results reveal that t‐BuOH can mediate the proton transfer in this step and significantly lower the energy barrier to 24.1 kcal/mol, which is also the highest energy barrier for the whole reaction. The work provides not only valuable clues for elucidating the detailed reaction mechanism for the invaluable NHC‐catalyzed oxidative reactions but also mechanistic insights for the rational design of novel NHC‐catalyzed oxidative reactions in the future.     

A joint FTIR,FT‐Raman and scaled quantum mechanical study of 1,3‐dibromo‐2,4,5,6‐tetra‐fluoro benzene (DTB) and 1,2,3,4,5‐pentafluoro benzene (PB)

The liquid phase FTIR and FT‐Raman spectra of 1,3‐dibromo‐2,4,5,6‐tetrafluoro benzene (DTB) and 1,2,3,4,5‐pentafluoro benzene (PB) were recorded in the regions 4000–400 cm⁻¹ and 4000–50 cm⁻¹, respectively. The spectra were interpreted with the aid of normal coordinate analysis following full structure opti1mization and force field calculations based on the density functional theory using the standard B3LYP/6‐31G* method and basis set combination. The scaled force field reproduced the experimental wavenumbers of the molecule for DTFB and PFB, respectively. The effects of halogen substituents on the structure and vibrational wavenumbers have been investigated. Assignments of fundamental modes were made based on the comparison between calculated and experimental results. Copyright © 2009 John Wiley & Sons, Ltd.     

Solvation structure of magnesium,zinc, and alkaline earth metal ions in N,N‐dimethylformamide,N,N‐dimethylacetamide,and their mixtures studied by means of Raman spectroscopy and DFT calculations—Ionic size and electronic effects on steric congestion

The solvation structure of magnesium, zinc(II), and alkaline earth metal ions in N,N‐dimethylformamide (DMF) and N,N‐dimethylacetamide (DMA), and their mixtures has been studied by means of Raman spectroscopy and DFT calculations. The solvation number is revealed to be 6, 7, 8, and 8 for Mg²⁺, Ca²⁺, Sr²⁺, and Ba²⁺, respectively, in both DMF and DMA. The δ (O C N) vibration of DMF shifts to a higher wavenumber upon binding to the metal ions and the shift Δν(= ν_bound − ν_free) becomes larger, when the ionic radius of the metal ion becomes smaller. The ν (N CH₃) vibration of DMA also shifts to a higher wavenumber upon binding to the metal ions. However, the shift Δν saturates for small ions, as well as the transition‐metal (II) ions, implying that steric congestion among solvent molecules takes place in the coordination sphere. It is also indicated that, despite the magnesium ion having practically the same ionic radius as the zinc(II) ion of six‐coordination, their solvation numbers in DMA are significantly different. DFT calculations for these metalsolvate clusters of varying solvation numbers revealed that not only solvent–solvent interaction through space but also the bonding nature of the metal ion plays an essential role in the steric congestion. The individual solvation number and the Raman shift Δν in DMF–DMA mixtures indicate that steric congestion is significant for the magnesium ion, but not appreciable for calcium, strontium, and barium ions, despite the solvation number of these metal ions being large. Copyright © 2006 John Wiley & Sons, Ltd.     

Theoretical investigations on 4,4′,5,5′‐tetranitro‐2,2′‐1H,1′H‐2,2′‐biimidazole derivatives as potential nitrogen‐rich high energy materials

The ―NH₂, ―NO₂, ―NHNO₂, ―C(NO₂)₃ and ―CF(NO₂)₂ substitution derivatives of 4,4′,5,5′‐tetranitro‐2,2′‐1H,1′H‐2,2′‐biimidazole were studied at B3LYP/aug‐cc‐pVDZ level of density functional theory. The crystal structures were obtained by molecular mechanics (MM) methods. Detonation properties were evaluated using Kamlet–Jacobs equations based on the calculated density and heat of formation. The thermal stability of the title compounds was investigated via the energy gaps (?E_{LUMO ? HOMO}) predicted. Results show that molecules T5 (D = 10.85 km·s^?1, P = 57.94 GPa) and T6 (D = 9.22 km·s^?1, P = 39.21 GPa) with zero or positive oxygen balance are excellent candidates for high energy density oxidizers (HEDOs). All of them appear to be potential explosives compared with the famous ones, octahydro‐1,3,5,7‐tetranitro‐1,3,5,7‐tetraazocane (HMX, D = 8.96 km·s^?1, P = 35.96 GPa) and hexanitrohexaazaisowurtzitane (CL‐20, D = 9.38 km·s^?1, P = 42.00 GPa). In addition, bond dissociation energy calculation indicates that T5 and T6 are also the most thermally stable ones among the title compounds. Copyright © 2014 John Wiley & Sons, Ltd.     

A Curtin–Hammett pentamethylene chain symmetrization process in the Bergman cyclization of an 11‐membered ring enediyne

Pentamethylene chain conformational effects for the Bergman cyclization of the 11‐membered ring enediyne, (3Z)‐3‐cycloundecene‐1,5‐diyne, 2, are examined theoretically with unrestricted Becke, three‐parameter, Lee–Yang–Parr/6‐31 G(d,p) calculations. A C₁ symmetric enediyne conformation was found to be the global minimum, where its nonsymmetric pentamethylene chain prevented π‐orbital alignment of the acetylene groups for C–C σ bond product formation. The Bergman cyclization of 2 was found to be conformationally dependent. In a Curtin–Hammett type process, the C₁ symmetric 2 inverts to one of the C_S or C₂ symmetric conformers required for the Bergman cyclization, which produced a C_S or C₂ symmetric 1,4‐diradical intermediate. The activation energy for the cyclization is slightly higher to reach the C₂ symmetry diradical compared with the C_S symmetry diradical. Copyright © 2012 John Wiley & Sons, Ltd.     

Theoretical investigation of two‐photon absorption and fluorescence properties of cypridina luciferin‐based derivatives: 2,3,5‐trisubstituted pyrazine compounds

Two‐photon fluorescent probe materials are significant for achieving observation of living phenomena in entire organs and tissues. To explore new materials with high fluorescence and large two‐photon absorption (TPA) cross section, a series of 2,3,5‐trisubstituted pyrazine derivatives were designed. Their equilibrium geometries, one‐photon absorption, TPA, and luminescence properties have been studied by using density functional theory (DFT), time‐dependent DFT, and Zerner's intermediate neglect of differential overlap program. The results show that the introduction of styrene groups to 2,3,5‐trisubstituted pyrazine derivatives can efficiently increase the conjugated effect and enhance the TPA activity. Moreover, the luminescence properties of 2,3,5‐trisubstituted pyrazine derivatives were compared, and the effect of three substituents on the fluorescence of trisubstituted pyrazine derivatives was analyzed by means of different contribution of the basis functions localized on pyrazine fragment into the highest occupied molecular orbital and lowest unoccupied molecular orbital. The oscillator strengths in the excited state (?_em) for the pyrazine derivatives substituted by styryl are larger than that of other derivatives with acetylamino and indole groups substituted at 2‐site and 5‐site of the pyrazine core, and the ?_em of 3‐indolyl pyrazine derivatives is larger than that of 3‐styrene pyrazine derivatives. It suggests that the styrene group has a great influence on the luminescence property. In addition, the indole group substituted at 3‐site of the pyrazine derivatives can also promote the fluorescence property. Copyright © 2013 John Wiley & Sons, Ltd.     

Spectroscopic and computational studies on self‐assembly complexes of bis(pyrrol‐2‐ ylmethyleneamine) ligands linked by alkyl spacers with Cu(II)

Bis(pyrrol‐2‐ylmethyleneamine) ligands and their mononuclear monomeric and dinuclear dimeric self‐assembly complexes with Cu(II) were investigated by means of IR and Raman spectroscopies and density functional theory. The ground‐state geometries were calculated by using the Becke Lee Yang Parr composite exchange‐correlation functional (B3LYP) and a combined basis set (LanL2DZ for Cu; 6–31G(d) for C, H, N), and they were compared with the single‐crystal X‐ray diffraction (XRD) structures. The DFT‐calculated Cu N bond lengths are generally higher by 0.001–0.040 Å than those determined through XRD. The vibrational spectra were also calculated at the same level of theory for the optimized geometries. The calculated wavenumbers were scaled by a uniform scaling factor and compared with the experimental fundamentals. The predicted spectra are in good agreement with the experimental ones with the deviations generally less than 30 cm⁻¹. In comparison with the spectra of the ligands, the coordination effect shifts the υ(CN) wavenumber by about 50 cm⁻¹ toward a lower value. Because of the weak intermolecular C H···Cu hydrogen bond, the Cu N stretching mode is shifted toward a lower wavenumber. Copyright © 2006 John Wiley & Sons, Ltd.     

Density functional theory study of the bis‐3‐benzo‐crown ethers and their complexes with alkali metal cations Na+, K+, Rb+ and Cs+

The binding interactions of bis‐3‐benzo‐15‐crown‐5 ethers and bis‐3‐benzo‐18‐crown‐6 ethers (neutral hosts) with a series of alkali metal cations Na⁺, K⁺, Rb⁺ and Cs⁺ (charged guests) were investigated using quantum chemical density functional theory. Different optimized structures, binding energies and various thermodynamic parameters of free crown ethers and their metal cation complexes were obtained based on the Becke, three‐parameter, Lee–Yang–Parr functional using mixed basis set (C, H, O, Na⁺ and K⁺ using 6‐31 g, and the heavier cation Rb⁺ and Cs⁺ using effective core potentials). Natural bond orbital analysis is conducted on the optimized geometric structures. The main types of driving force host–guest interactions are investigated. The electron donating O offers a lone pair of electrons to the contacting LP* (1‐center valence antibond lone pair) orbitals of metal cations. The bis‐3‐benzocrown ethers are assumed to have sandwich‐like conformations, considering the binding energies to gauge the exact interactions with alkali cations. It is found that there are two different types of complexes: one is a tight ion pair and the other is a separated ion pair. Copyright © 2011 John Wiley & Sons, Ltd.     

Structural dynamics of 4‐pyrimidone in lower‐lying excited States

The structural dynamics of 4‐pyrimidone (4PMO) in the A‐ and B‐band absorptions was studied by using the resonance Raman spectroscopy combined with quantum chemical calculations to better understand whether the excited state intramolecular proton‐transfer (ESIPT) reaction occurs in Franck–Condon regions or not. The transition barrier for the ground state proton‐transfer tautomerization reaction between 3(H) (I) and hydroxy (II) was determined to be 165 kJ·mol⁻¹ in vacuum on the basis of the B3LYP/6‐311++G(d,2p) level of theory calculations. Two ultraviolet absorption bands of 4PMO were, respectively, assigned as π_H→π*_L and π_H→π*_L+1 transitions. The vibrational assignments were done on the basis of the Fourier transform (FT)‐Raman and FT‐infrared (IR) measurements, the density‐functional theory computations and the normal mode analysis. The A‐ and B‐band resonance Raman spectra of 4PMO were measured in water, methanol and acetonitrile. The structural dynamics of 4PMO was obtained through the analysis of the resonance Raman intensity pattern. We discuss the similarities in the structural dynamics of 4PMO and 2‐thiopyrimidone (2TPM), and the results were used to correlate to the intramolecular hydrogen‐atom‐transfer process as observed by matrix‐isolation IR experiments for 4PMO. A variety of NH/CH bend modes + C = O stretch mode mark the hydrogen‐detachment‐attachment or ESIPT reaction initiated in Franck–Condon region for 4PMO and 2TPM. Copyright © 2013 John Wiley & Sons, Ltd.     

Betulin and its natural resource as potential anticancer drug candidate seen by FT‐Raman and FT‐IR spectroscopy

The Fourier transform Raman and IR spectra of betulin (lup‐20(29)‐ene‐3β,28‐diol) crystalline powder were recorded and analyzed. The vibrational wavenumbers and the corresponding vibrational assignments were theoretically studied using the Gaussian 03 package. The calculated vibrational wavenumbers with the B3LYP density functionals are generally consistent with the observed spectra. A complete vibrational characterization of betulin modes has been proposed here for the first time. Based on the vibrational analysis, two direct applications of the results have been described. It was shown that the outer bark of Betula Pendula Roth (the birch tree) contains betulin as a major component along with minor amounts of betulinic acid (BA), lupeol and other pentacyclic triterpenes derivatives. Since the major disadvantage of betulin is its low solubility, giving rise to serious problems in making pharmaceutical formulations, several guest–host type of complexes of betulin–cyclodextrins have been prepared and analyzed using FT‐Raman spectroscopy. Based on the vibrational analysis, it was concluded that the OH and CH₂OH functional groups are free from chemical interactions with the cyclodextrin cavity. Copyright © 2010 John Wiley & Sons, Ltd.     

Theoretical investigation on the excited‐state intramolecular proton transfer mechanism of 2‐(2′‐benzofuryl)‐3‐hydroxychromone

Spectroscopic studies on excited‐state proton transfer of a new chromophore 2‐(2′‐benzofuryl)‐3‐hydroxychromone (BFHC) have been reported recently. In the present work, based on the time‐dependent density functional theory (TD‐DFT), the excited‐state intramolecular proton transfer (ESIPT) of BFHC is investigated theoretically. The calculated primary bond lengths and angles involved in hydrogen bond demonstrate that the intramolecular hydrogen bond is strengthened. In addition, the phenomenon of hydrogen bond reinforce has also been testified based on infrared (IR) vibrational spectra as well as the calculated hydrogen bonding energies. Further, hydrogen bonding strengthening manifests the tendency of excited state proton transfer. Our calculated results reproduced absorbance and fluorescence emission spectra of experiment, which verifies that the TD‐DFT theory we used is reasonable and effective. The calculated Frontier Molecular Orbitals (MOs) further demonstrate that the excited state proton transfer is likely to occur. According to the calculated results of potential energy curves along O―H coordinate, the potential energy barrier of about 14.5 kcal/mol is discovered in the S₀ state. However, a lower potential energy barrier of 5.4 kcal/mol is found in the S₁ state, which demonstrates that the proton transfer process is more likely to happen in the S₁ state than the S₀ state. In other words, the proton transfer reaction can be facilitated based on the photo‐excitation effectively. Moreover, the phenomenon of fluorescence quenching could be explained based on the ESIPT mechanism. Copyright © 2015 John Wiley & Sons, Ltd.     

Computer simulations and analysis of structural and energetic features of crystalline cage energetic compound: 2, 4, 6, 8, 12‐pentanitro‐10‐(3, 5, 6‐trinitro (2‐pyridyl))‐2, 4, 6, 8, 12‐hexaazatetracyclo [5.5.0.03,11.05,9]dodecane

First principles molecular orbital and plane‐wave ab initio calculations have been used to investigate the structural and energetic properties of a new cage compound 2, 4, 6, 8, 12‐pentanitro‐10‐(3, 5, 6‐trinitro (2‐pyridyl))‐2, 4, 6, 8, 12‐hexaazatetracyclo [5.5.0.0^3,11.0^5,9]dodecane (PNTNPHATCD) in both the gas and solid phases. The molecular orbital calculations using the density functional theory methods at the B3LYP/6‐31G(d,p) level indicate that both the heat of formation and strain energy of PNTNPHATCD are larger than those of 2, 4, 6, 8, 10, 12‐hexanitro‐2, 4, 6, 8, 10, 12‐hexaazatetracyclo [5.5.0.0.0] dodecane (CL‐20). The infrared spectra and the thermodynamic property in gas phase were predicted and discussed. The calculated detonation characteristics of PNTNPHATCD estimated using the Kamlet–Jacobs equation equally matched with those of CL‐20. Bond‐breaking results on the basis of natural bond orbital analysis imply that C–C bond in cage skeleton, C–N bond in pyridine, and N–NO₂ bond in the side chain of cage may be the trigger bonds in the pyrolysis. The structural properties of PNTNPHATCD crystal have been studied by a plane‐wave density functional theory method in the framework of the generalized gradient approximation. The crystal packing predicted using the Condensed‐phase Optimized Molecular Potentials for Atomistic Simulation Studies (COMPASS) force fields belongs to the Pbca space group, with the lattice parameters a = 20.87 Å, b = 24.95 Å, c = 7.48 Å, and Z = 8, respectively. The results of the band gap and density of state suggest that the N–NO₂ bond in PNTNPHATCD may be the initial breaking bond in the pyrolysis step. As the temperature increases, the heat capacity, enthalpy, and entropy of PNTNPHATCD crystal all increase, whereas the free energy decreases. Considering that the cage compound has the better detonation performances and stability, it may be a superior high energy density compound. Copyright © 2015 John Wiley & Sons, Ltd.     

Computational design of tetrazolone‐based high‐energy density energetic materials: Property prediction and decomposition mechanism

The density functional theory methods are used to design a series of new highly energetic tetrazolone‐based molecules by the combination of the linked tetrazolone framework and versatile substitutes. The molecular and electronic structures, physicochemical, and energetic properties were analyzed and predicted. The decomposition mechanisms were computationally simulated, and 3 potential decomposition channels were proposed. These newly designed tetrazolone‐based compounds show high densities (up to 2.08 g/cm³) and highly positive heats of formation (407.0‐1377.9 kJ/mol) due to all right content of nitrogen and oxygen. Most of them exhibit good detonation velocity (8.31‐9.62 km/s) and detonation pressure (32.40‐43.86 GPa), and some are comparative to excellent explosive CL‐20. Results show that compounds 6 , 10 , 11 , 12 , 15 , 16 , 17 , 22 , 23 , and 24 own superior detonation performance than widely used explosive HMX and may be promising candidates of green high‐performance energetic materials.     

Theoretical design on a new double functional device of 2,2′‐bipyridine‐embedded N‐(9‐pyrenyl methyl)aza‐15‐crown‐5

Theoretical design on a new molecular switch and fluorescent chemosensor double functional device of aza‐crown ether (2,2′‐dipyridine‐embedded N‐(9‐anthraceneyl(pyrenyl)methyl)aza‐15‐crown‐5) was explored. The interactions between ligands and a series of alkaline earth metal cations (Mg²⁺, Ca²⁺, Sr²⁺, and Ba²⁺) were investigated. The fully optimized geometry structures of the free ligands ( L _1, L ₂) and their metal cation complexes ( L ₁/M²⁺, L ₂/M²⁺) were calculated with the B3LYP/6‐31G(d) method. The natural bond orbital analysis, which is based on optimized geometric structures, was used to explore the interaction of L ₁/M²⁺, L ₂/M²⁺ molecules. The absorption spectra of L _1, L ₂, L ₁/M²⁺, and L ₂/M²⁺, and their excited states were studied by time‐dependent density functional theory. A new type molecular device L ₂(2,2′‐dipyridine‐embedded N‐(9‐pyrenyl methyl)aza‐15‐crown‐5) is designed, which not only has the selectivity for Sr²⁺, and construct allosteric switch, but also has fluorescent sensor performance.