The photoisomerization mechanism of azobenzene: a semiclassical simulation of nonadiabatic dynamics

We have simulated the photoisomerization dynamics of azobenzene, taking into account internal conversion and geometrical relaxation processes, by means of a semiclassical surface hopping approach. Both n-->pi* and pi-->pi* excitations and both cis-->trans and trans-->cis conversions have been considered. We show that in all cases the torsion around the N==N double bond is the preferred mechanism. The quantum yields measured are correctly reproduced and the observed differences are explained as a result of the competition between the inertia of the torsional motion and the premature deactivation of the excited state. Recent time-resolved spectroscopic experiments are interpreted in the light of the simulated dynamics.     

Acceleration of self‐consistent field convergence in ab initio molecular dynamics simulation with multiconfigurational wave function

The Lagrange interpolation of molecular orbital (LIMO) method, which reduces the number of self‐consistent field iterations in ab initio molecular dynamics simulations with the Hartree–Fock method and the Kohn–Sham density functional theories, is extended to the theory of multiconfigurational wave functions. We examine two types of treatments for the active orbitals that are partially occupied. The first treatment, as denoted by LIMO(C), is a simple application of the conventional LIMO method to the union of the inactive core and the active orbitals. The second, as denoted by LIMO(S), separately treats the inactive core and the active orbitals. Numerical tests to compare the two treatments clarify that LIMO(S) is superior to LIMO(C). Further applications of LIMO(S) to various systems demonstrate its effectiveness and robustness. © 2014 Wiley Periodicals, Inc.     

Wavelet transform analysis of ab initio molecular dynamics simulation: application to core-excitation dynamics of BF3

We propose a novel analysis method of ab initio molecular dynamics (AIMD) simulation using a continuous wavelet transform (c-WT) technique. The c-WT technique, one of the time-frequency signal analysis methods, provides a clear view of the dynamical information in time developments. Combined with the auto-correlation function of velocity by AIMD simulation, c-WT analysis enables us to well understand dynamical distribution, such as the vibrational properties following a change of electronic structure in a molecular system. As a practical application, AIMD simulation of core-excited BF(3) (B1s --> 2a(2) (')) is illustrated. AIMD simulation leads to the change of vibrational motion as well as structural deformation by core-excitation. The c-WT analysis clarifies the relationship between structural deformation and the related significant vibrational modes in core-excitation within 50 fs.     

The photoisomerization of 11‐cis‐retinal protonated schiff base in gas phase: Insight from spin‐flip density functional theory

This extensive theoretical study employed the spin‐flip density functional theory (SFDFT) method to investigate the photoisomerization of 11‐cis‐retinal protonated Schiff base (PSB11) and its minimal model tZt‐penta‐3,5‐dieniminium cation (PSB3). Our calculated results indicate that SFDFT can perform very well in describing the ground‐ and excited‐state geometries of PSB3 and PSB11. We located the conical intersection (CI) point and constructed the photoisomerization reaction path of PSB3 and PSB11 by using the SFDFT method. To further verify the SFDFT results, we computed the energy profiles along the constructed linearly interpolated internal coordinate (LIIC) pathways by using high‐level theoretical methods, such as the EOM‐CCSD, CR‐EOM‐CCSD(T), CASPT2, NEVPT2, and XMCQDPT2 methods. The SFDFT method predicts that the photoisomerization of PSB3 is barrierless, in accordance with previous complete‐active‐space self‐consistent‐field (CASSCF) results. However, an energy barrier is predicted along the LIIC pathways of PSB11. This finding is different from previous CASSCF results and may indicate that the photoisomerization of PSB11 in gas phase is similar to that in solution. However, the higher spin contamination of the SFDFT method in the vicinity of the CI point caused the located CI geometry to deviate from that of the real CI. In addition, the LIIC pathways are only approximations to the minimum energy path (MEP). Thus, further experimental and theoretical studies are needed to verify the existence of an energy barrier along the photoisomerization reaction path of PSB11 in gas phase. © 2013 Wiley Periodicals, Inc.     

A single‐molecule reaction cascade: First‐principles molecular dynamics simulation

The success of mechanochemistry is continued with the targeted organic synthesis of functional nano‐scale devices. In the present theoretical study, first principles molecular dynamics simulations are performed for a recently synthesized three‐ring system that functions as a molecular reaction cascade. Mechanochemical and photochemical reaction conditions are investigated. The system was designed in a way that three bonds would break consecutively in mechanochemical and sonochemical setups. We succeeded to simulate the reaction mechanisms with first‐principles molecular dynamics simulations and discuss the stereochemistry.     

Distinguishing between keto–enol and acid–base forms of firefly oxyluciferin through calculation of excited‐state equilibrium constants

Although recent years have seen much progress in the elucidation of the mechanisms underlying the bioluminescence of fireflies, there is to date no consensus on the precise contributions to the light emission from the different possible forms of the chemiexcited oxyluciferin (OxyLH₂) cofactor. Here, this problem is investigated by the calculation of excited‐state equilibrium constants in aqueous solution for keto–enol and acid–base reactions connecting six neutral, monoanionic and dianionic forms of OxyLH₂. Particularly, rather than relying on the standard Förster equation and the associated assumption that entropic effects are negligible, these equilibrium constants are for the first time calculated in terms of excited‐state free energies of a Born–Haber cycle. Performing quantum chemical calculations with density functional theory methods and using a hybrid cluster‐continuum approach to describe solvent effects, a suitable protocol for the modeling is first defined from benchmark calculations on phenol. Applying this protocol to the various OxyLH₂ species and verifying that available experimental data (absorption shifts and ground‐state equilibrium constants) are accurately reproduced, it is then found that the phenolate‐keto‐OxyLH^– monoanion is intrinsically the preferred form of OxyLH₂ in the excited state, which suggests a potential key role for this species in the bioluminescence of fireflies. © 2014 Wiley Periodicals, Inc.     

Nonadiabatic relaxation dynamics of water anion cluster and its isotope effects by ring‐polymer molecular dynamics simulation

We have applied a recently developed hybrid quantum ring‐polymer molecular dynamics method to the nonadiabatic p → s relaxation dynamics in water anion clusters to understand the isotope effects observed in previous experiments. The average relaxation times for (H₂O)₅₀^? and (D₂O)₅₀^? were calculated at 120 and 207 fs, respectively, and are comparable to the experimental results. Therefore, we conclude that nuclear quantum effects play an essential role in understanding the observed isotope effects for water anion cluster nonadiabatic dynamics. The nonadiabatic relaxation mechanisms are also discussed in detail. © 2014 Wiley Periodicals, Inc.     

An acetatopalladium(II) complex with 1‐benzyl‐N‐(3,5‐di‐tert‐butylsalicylidene)piperidin‐4‐amine: Synthesis,structure and catalytic applications in Suzuki–Miyaura coupling of arylboronic acids with hydroxyaryl halides

The Schiff base 1‐benzyl‐N ‐(3,5‐di‐tert ‐butylsalicylidene)piperidin‐4‐amine (HL) and its acetatopalladium(II) complex having the formula [Pd(L)(OAc)] were synthesized. Both HL and [Pd(L)(OAc)] were characterized using elemental analysis and various spectroscopic (infrared, UV–visible, ¹H NMR and ¹³C NMR) and mass spectrometric measurements. The molecular structure of the complex was determined using X‐ray crystallographic analysis. In the complex, the pincer‐like NNO‐donor L⁻ and the monodenate OAc⁻ provide a distorted square‐planar N₂O₂ coordination environment around the metal centre. The physicochemical properties and the spectroscopic features of [Pd(L)(OAc)] are consistent with its molecular structure. The complex was found to be an effective catalyst for the Suzuki–Miyaura cross‐coupling reactions of hydroxyaryl halides with arylboronic acids in predominantly aqueous media. The reactions afforded hydroxybiaryl products in good to excellent yields with a wide substrate scope.     

N‐Germyl derivatives of sulfacetamide and ortho‐(sulfonamido)phenylamines: characterization of N‐[o‐(N′,N′‐dimethylsulfonamido)phenyl]‐N‐dimesitylgermaimine

Triethylgermylation of sulfacetamide occurs on the sulfonamido nitrogen in competition with the 1,2 addition of the starting triethylgermyl dimethylamine on the carbonyl group. Thermal decomposition in the presence of dimethylamine yields N‐triethylgermylsulfanilamide. Stable 1:1 sulfacetamide–DBU and 1:1 sulfacetamide–Et₃N complexes were isolated and fully characterized in the course of dehydrochlorination reactions. o‐Sulfonamidophenylamine yields N,N′‐bis‐triethylgermylated derivatives, whereas o‐(N,N‐dimethylsulfonamido)phenylamine leads to monogermylated compounds. The N‐dimethylaminodimesitylgermyl derivative is thermally stable. Dehydrohalogenation of the N‐dimesitylfluorogermyl compound leads to the thermally stable but water sensitive N‐[o‐(N′,N′‐dimethylsulfonamido)phenyl]‐N‐dimesitylgermaimine. Copyright © 2003 John Wiley & Sons, Ltd.     

Implicit and explicit solvent models for modeling a bifunctional arene ruthenium hydrogen‐storage catalyst: A classical and ab initio molecular simulation study

Classical and ab initio, density functional theory‐ and semiempirical‐based molecular simulation, including molecular dynamics, have been carried out to compare and contrast the effect of explicit and implicit solvation representation of tetrahydrofuran (THF) solvent on the structural, energetic, and dynamical properties of a novel bifunctional arene ruthenium catalyst embedded therein. Particular scrutiny was afforded to hydrogen‐bonding and energetic interactions with the THF liquid. It was found that the presence of explicit THF solvent molecules is required to capture an accurate picture of the catalyst's structural properties, particularly in view of the importance of hydrogen bonding with the surrounding THF molecules. This has implications for accurate modeling of the reactivity of the catalyst. © 2014 Wiley Periodicals, Inc.     

Simultaneous construction of a polyether backbone and a variety of keto side chains by three‐component polycondensation: An improved method for the use of a variety of silyl enol ethers

For the synthesis of polyethers with a variety of keto side chains in a one‐step reaction, the three‐component polycondensation of dialdehydes, diol disilyl ethers, and silyl enol ethers of ketones was investigated. The method of monomer addition strongly affected the molecular weight of polymers and was optimized to yield high molecular weight polymers by model reactions. A variety of dialdehydes, diol disilyl ethers, and silyl enol ethers were polymerized in the presence of a catalytic amount of triphenylmethyl (trityl) perchlorate in CH₂Cl₂ at −78 °C according to the method of monomer addition. This polymer synthesis was unusual in that it concurrently constructed both the polyether backbone and the keto side chains from three starting compounds. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 179–188, 2000     

Negative charge induced dissociation: fragmentation of deprotonated N‐benzylidene‐2‐hydroxylanilines in electrospray ionization mass spectrometry

Unimolecular reactivities of different N‐benzylidene‐2‐hydroxylaniline anions were investigated in gas phase by electrospray ionization tandem mass spectrometry. All the collision‐induced dissociation spectra of N‐benzylidene‐2‐hydroxylaniline anions show similar ions at phenyl anions, neutral loss of benzonitrile and benzoxazole anions, respectively. The possible fragmentation pathway was probed through deuterium labeling and various group substituents experiments. Computational results were applied to shed light on the mechanism of fragmentation patterns. The proton in the CH=N is reactive in the formation of the concerned ions. Its direct transfer to the oxygen results in 2‐hydroxyphenyl anion. Proton abstraction between benzoxazole and phenyl anion leads to the formation of benzene and benzoxazole anion. Copyright © 2014 John Wiley & Sons, Ltd.     

1H, 13C and 15N NMR spectroscopic,x‐ray structural and ab initio/HF studies on nitramino and N‐alkylamino‐4‐nitro derivatives of pyridine N‐oxides and pyridines

The ¹H, ¹³C and ¹⁵N NMR spectra in DMSO‐d₆ were measured for eight nitraminopyridine N‐oxides, ten 4‐nitropyridine N‐oxides, four 2‐nitraminopyridines and five 4‐nitropyridines. Their chemical shift assignments are based on PFG ¹H,X (X = ¹³C and ¹⁵N) HMQC and HMBC experiments. The relative energies for the tautomers of two nitraminopyridine N‐oxides were determined by ab initio HF/6–311G** calculations. A single‐crystal x‐ray structural analysis was made for 4‐methyl‐2‐nitraminopyridine: C₆H₇O₂N₃, M = 153.15, triclinic, space group P‐1 (No. 2), a = 7.0275(4), b = 6.8034(3), c = 8.6086(5) Å, α = 103.620(2), β = 90.309(2), γ = 122.215(3)°, V = 334.11(3) ų, Z = 2. Copyright © 2003 John Wiley & Sons, Ltd.     

Thermodynamic compatibility of actives encapsulated into PEG‐PLA nanoparticles: In Silico predictions and experimental verification

Achieving optimal solubility of active substances in polymeric carriers is of fundamental importance for a number of industrial applications, including targeted drug delivery within the growing field of nanomedicine. However, its experimental optimization using a trial‐and‐error approach is cumbersome and time‐consuming. Here, an approach based on molecular dynamics (MD) simulations and the Flory–Huggins theory is proposed for rapid prediction of thermodynamic compatibility between active species and copolymers comprising hydrophilic and hydrophobic segments. In contrast to similar methods, our approach offers high computational efficiency by employing MD simulations that avoid explicit consideration of the actual copolymer chains. The accuracy of the method is demonstrated for compatibility predictions between pyrene and nile red as model dyes as well as indomethacin as model drug and copolymers containing blocks of poly(ethylene glycol) and poly(lactic acid) in different ratios. The results of the simulations are directly verified by comparison with the observed encapsulation efficiency of nanoparticles prepared by nanoprecipitation. © 2016 Wiley Periodicals, Inc.     

Brownian dynamics simulation of two‐dimensional nanosheets under biaxial extensional flow

The morphology dynamics of two‐dimensional nanosheets under extensional flow are investigated using a coarse‐grained model. Nanosheets (graphene, BNNS, MX₂) are promising materials for a variety of materials and electronics applications. Extensional flow fields are often present during dispersion processing, such as spin coating. Both nanosheet properties (e.g., moduli, size) and processing parameters (e.g., extension rate) can have a significant impact on the nanosheet morphology and thus, the structure and properties of the bulk material. Our previously developed dimensionless Brownian dynamics methodology is used to explore biaxial extensional flow. Nanosheets exhibit a flat conformation under extensional flow for high bending moduli and an extended “washrag” conformation for low bending moduli. Intrinsic extensional viscosity increases with strain before reaching a plateau. The intrinsic viscosity exhibits a weak power law with nanosheet molecular weight. These simulation results allow for experimental control over morphology as a function of nanosheet properties and flow type and strength. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 1247–1253     

α‐keto‐β‐diimine nickel‐catalyzed olefin polymerization: Effect of ortho‐aryl substituents and preparation of stereoblock copolymers

A series of α‐keto‐β‐diimine nickel complexes (Ar‐N = C(CH₃)‐C(O)‐C(CH₃)=N‐Ar)NiBr₂; Ar = 2,6‐R‐C₆H₃‐, R = Me, Et, iPr, and Ar = 2,4,6‐Me₃‐C₆H₃‐) was prepared. All corresponding ligands are unstable even under an inert atmosphere and in a freezer. Stable copper complex intermediates of ligand synthesis and ethyl substituted nickel complex were isolated and characterized by X‐ray. All nickel complexes were used for the polymerization of ethene, propylene, and hex‐1‐ene to investigate their livingness and the extent of chain‐walking. Low‐temperature propene polymerization with less bulky ortho‐substituents was less isospecific than the one with isopropyl derivative. Propene stereoblock copolymers were prepared by iPr derivative combining the polymerization at low temperature to prepare isotactic polypropylene (PP) block and at a higher temperature, supporting chain‐walking, to obtain amorphous regioirregular PP block. Alternatively, a copolymerization of propene with ethene was used for the preparation of amorphous block. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 2440–2449     

Synthesis and polymerization of fluorinated monomers bearing a reactive lateral group. XII. Copolymerization of vinylidene fluoride with 2,3,3‐trifluoroprop‐2‐enol

An improved synthesis of 2,3,3‐trifluoroprop‐2‐enol (FA1) and its copolymerization in solution with vinylidene fluoride (VDF, or 1,1‐difluoroethylene) initiated by tert‐butyl peroxypivalate are presented. A new synthesis of FA1, with NaH and lithium diisopropylamine as bases, from 2,2,3,3‐tetrafluoropropanol is described. A series of nine copolymerization reactions were investigated from initial [VDF]₀/[FA1]₀ molar ratios of 9.1/90.9 to 94.2/5.8. The copolymer compositions were calculated via ¹⁹F NMR spectroscopy. From the Tidwell–Mortimer method, the reactivity ratios of both comonomers were determined (r_FA1 = 0.11 ± 0.22 and r_VDF = 0.83 ± 0.77 at 50°C), and they showed an azeotropic point. Alfrey and Price's Q and e values of FA1 were calculated to be 0.0178 (from Q_VDF = 0.008), 0.039 (from Q_VDF = 0.015), and 0.275 (from Q_VDF = 0.036) and 2.74 (vs e_VDF = 1.20), 2.04 (vs e_VDF = 0.50), and 1.94 (vs e_VDF = 0.4), respectively, and they indicated that FA1 is an electron‐accepting monomer. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3634–3643, 2002     

Short-time Fourier transform analysis of ab initio molecular dynamics simulation: collision reaction between CN and C4H6

Collision reactions between cyano radical (CN) and dimethylacetylene (C4H6) are thought to occur in the atmosphere of Saturn's moon Titan. However, it is difficult to reproduce reactions occurring in unique environments to study their dynamical processes. In this study, collision reactions between CN and C4H6 were investigated using ab initio molecular dynamics (AIMD) simulations. The simulation results were categorized into three kinds: nonreactive collision, incorporation, and substitution. Short-time Fourier transform analysis of velocity autocorrelation functions obtained by the AIMD simulations, which has been recently developed by our research group, was performed to examine the nonequilibrium condition of the vibrational states. Spectrograms, which correspond to the time evolution of power spectra, clarify the relationship between the three reaction channels and the dynamical changes of the vibrational states.