DFT simulations and vibrational analysis of FTIR and FT‐Raman spectra of 2‐amino‐4,6‐dihydroxypyrimidine

This work deals with the vibrational spectroscopy of 2‐amino‐4,6‐dihydroxy pyrimidine (ADHP) by means of quantum chemical calculations. The mid‐ and far FTIR and FT‐Raman spectra were measured in the condensed state. The fundamental vibrational wavenumbers and intensity of vibrational bands were evaluated using density functional theory (DFT) with the standard B3LYP/6‐311 + G** methods and basis set combinations, and were scaled using various scale factors, which yielded good agreement between the observed and calculated wavenumbers. The vibrational spectra were interpreted with the aid of normal coordinate analysis based on the scaled density functional force field. The results of the calculations were applied to simulate the infrared and Raman spectra of the title compound, which showed excellent agreement with the observed spectra. Copyright © 2008 John Wiley & Sons, Ltd.     

Ionic liquid structure: the conformational isomerism in 1‐butyl‐3‐methyl‐imidazolium tetrafluoroborate ([bmim][BF4])

As a probe of local structure, the vibrational properties of the 1‐butyl‐3‐methylimidazolium tetrafluoroborate [bmim][BF₄] ionic liquid were studied by infrared (IR), Raman spectroscopy, and ab initio calculations. The coexistence of at least four [bmim]⁺ conformers (GG, GA, TA, and AA) at room temperature was established through unique spectral responses. The Raman modes characteristic of the two most stable [bmim]⁺ conformers, GA and AA, according to the ab initio calculations, increase in intensity with decreasing temperature. To assess the total spectral behavior of the ionic liquid both the contributions of different [bmim]⁺ conformers and the [bmim]⁺− [BF₄]⁻ interactions to the vibrational spectra are discussed. Copyright © 2008 John Wiley & Sons, Ltd.     

Synthesis and structural study of 2′‐ and 2′,6′‐positioned methyl‐ and nitro‐substituted 3‐(arylhydrazono)pentane‐2,4‐diones

A systematic series of ortho‐methyl‐ and nitro‐substituted arylhydrazones 2–6 formed by Japp–Klingemann reaction between pentane‐2,4‐dione and the respective aryldiazonium salts have been synthesized and studied by X‐ray crystal structure analysis, with added quantum chemical calculations. The optimized molecular geometries based on DFT calculations, enabling determination of relevant rotational barriers, and the calculated bond and ring critical points, using the method of ‘atoms in molecules’, were found to correspond with the experimental data, involving specific molecular conformations and hydrogen‐bonded ring structure dependent on the ortho‐substitution, thus making possible reliable structural prediction of this compound class. Copyright © 2007 John Wiley & Sons, Ltd.     

Experimental vibrational spectra (Raman,infrared) and DFT calculations on monomeric and dimeric structures of 2‐ and 6‐bromonicotinic acid

In this work, the Fourier transform infrared and Raman spectra of 2‐bromonicotinic acid and 6‐bromonicotinic acid (abbreviated as 2‐BrNA and 6‐BrNA, C₆H₄BrNO₂) have been recorded in the region 4000–400 and 3500–50 cm⁻¹. The optimum molecular geometry, normal mode wavenumbers, infrared intensities and Raman scattering activities, corresponding vibrational assignments and intermolecular hydrogen bonds were investigated with the help of B3LYP density functional theory (DFT) method using 6‐311++G(d,p) basis set. Reliable vibrational assignments were made on the basis of total energy distribution (TED) calculated with scaled quantum mechanical (SQM) method. From the calculations, the molecules are predicted to exist predominantly as the C1 conformer. Copyright © 2009 John Wiley & Sons, Ltd.     

Molecular structure and vibrational spectra of 3 (or 4 or 6)‐methyl‐5‐nitro‐2‐pyridinethiones: FT‐IR,FT‐Raman and DFT quantum chemical calculations

IR and Raman spectra (RS) of polycrystalline 3‐(or 4 or 6)‐methyl‐5‐nitro‐2‐pyridinethione have been measured and analyzed by means of density functional theory (DFT) quantum chemical calculations. The B3LYP/6‐311G(2d,2p) approach has been applied for both the thiol and thione tautomers due to the possibility of the formation of these two thiole forms. Molecular structures of these compounds have been optimized starting from different molecular geometries of the thiol group and thione group. Two conformations of the 2‐mercaptopyridine, trans and cis, have been taken into account. It was shown that the studied compounds appear in the solid state in the thione form. The effect of the hydrogen‐bond formation in the studied compounds has been considered. Copyright © 2008 John Wiley & Sons, Ltd.     

Theoretical study of optical and electronic properties of the bis‐dipolar diphenylamino‐endcapped oligoarylfluorenes as promising light emitting materials

We present a detailed study of the structural, electronic, and optical properties of the bis‐dipolar emissive oligoarylfluorenes, OF(2)Ar‐NPhs. The aim of our quantum‐chemical calculations is to investigate the role of the transition and the influence of the optical properties of the various central aryl cores in the oligoarylfluorenes. Geometry optimizations were performed for the ground‐state and for the first electronically excited‐state. The absorption and emission spectra were calculated using time‐dependent density functional theory (TD‐DFT). The results show that the HOMO, LUMO, energy gap, ionization potentials (IP), electron affinities (EA) and reorganization energy (λ) of the oligoarylfluorenes are significantly affected by the electronic withdrawing property and the conjugated length of the central aryl core. Consistently, the stronger the electron withdrawing strength, the lower the LUMO energy is. This thus improves the electron‐accepting and transporting properties by the low LUMO energy levels. The absorption and emission spectra of this series of bis‐dipolar molecules exhibit red shifts to some extent by the electronic nature of the electron affinitive central core in the oligoarylfluorenes. All the calculated results show that the oligoarylfluorenes are promising as useful light emitting materials for OLEDs. Copyright © 2007 John Wiley & Sons, Ltd.     

A computational study (DFT,MP2, and GIAO‐DFT) of substituent effects on protonation regioselectivity in β,β‐disubstituted vinyldiazonium cations: formation of highly delocalized carbenium/diazonium dications

Protonation reactions were studied by quantum‐chemical theoretical methods (DFT and MP2) for a series of β,β‐disubstituted vinyldiazonium cations ( 1 ⁺ – 14 ⁺ ), bearing stabilizing electron‐releasing groups (H₃CO? , (H₃C)₂N? , H₃C? , (H₃C)₃Si? , as well as halogens F, Cl). Taking into account the various mesomeric forms that these species can represent, protonations at C_α, at the β‐substituent, and at N_β were considered. The energetically most favored pathway in all cases was C_α protonation, which formally corresponds to trapping of the mesomeric diazonium ylid. Based on the computed properties (optimized geometries, NPA‐charge densities, and multinuclear GIAO‐NMR chemical shifts), the resulting dications can best be viewed as carbenium/diazonium dications, in which the carbocation is further delocalized into the β‐substituent. For the α‐nitro derivative 15 , protonation of the nitro group was predicted to be the most favored reaction, while C_α‐ and N_β‐protonation resulted in the loss of the nitronium ion. Copyright © 2009 John Wiley & Sons, Ltd.     

Lithium solvation in a PMMA membrane plasticized by a lithium‐conducting ionic liquid based on 1‐butyl‐3‐methylimidazolium bis(trifluoromethanesulfonyl)imide

The Raman and Infrared (IR) spectra of poly(methyl methacrylate) (PMMA) membranes plasticized by ionic liquids of the (1 − x)[1‐butyl‐3‐methylimidazolium bis(trifluoromethanesulfonyl)imide (BMITFSI)],xLiTFSI type, where BMI⁺ is the 1‐butyl‐3‐methylimidazolium cation and TFSI⁻ the bis(trifluoromethanesulfonyl)imide anion, are analyzed for a lithium bis(trifluoromethane sulfone)imide (LiTFSI) mole fraction x = 0.23 and PMMA contents from 0 to 50 wt%. The lithium is found to have an average coordination of about three CO groups and less than one TFSI⁻ anion. It plays the role of a cross‐linker between the ester groups of PMMA and the nonvolatile ionic liquid. Addition of PMMA to the (1 − x)(BMITFSI),xLiTFSI ionic liquid lowers the conductivity but might improve the lithium transference number by transforming the [Li(TFSI)₂]⁻ anionic clusters present in the pure ionic liquid into a mixed coordination by ester groups and TFSI⁻ anions. Copyright © 2008 John Wiley & Sons, Ltd.     

Structure and properties of α‐cyclo[N]thiophenes as potential electronic materials – a theoretical study

Density functional theory (DFT) calculations of ring‐shaped α‐cyclo[N]thiophenes with N = 2 to N = 18 have been performed for ideal structures of high symmetry (point groups C_nv and D_nh) and for optimum energy structures of lower symmetry (D_2d, C_s, C_2v, C_i or C₁). Whereas the first three members of the series behave exceptionally the higher members are typical cyclothiophenes consisting of weakly interacting thiophene rings. In contrast to neutral compounds, cations and dications of cyclothiophenes with N ≥5 exhibit pronounced electron delocalizations along the carbon backbone. However, if the functional B3LYP is replaced by BH cations of large ring‐size cations show polaron‐type charge defects. According to broken symmetry DFT calculations dications with N = 14 and N = 18 have biradical character. These structures correspond to two‐polaron‐type structures rather than to dipolarons. The calculated vertical ionization energies of cyclo[N]thiophene are comparable with those of oligo[N]thiophenes of the same number of thiophene rings but the calculated absolute energies are probably too low at large ring size. Cyclothiophenes absorb light of lower energies than the related oligothiophenes. Cyclothiophenes belong to the strongly absorbing organic chromophores. In case of high molecular symmetry some of the excited states of cyclothiophenes are degenerate. The degeneracy is lifted with lower symmetries but the general absorption feature remains. The theoretical results are discussed with respect to recent experimental findings. Copyright © 2007 John Wiley & Sons, Ltd.     

New insights on surface‐enhanced Raman scattering based on controlled aggregation and spectroscopic studies,DFT calculations and symmetry analysis for 3,6‐bi‐2‐pyridyl‐1,2,4,5‐tetrazine adsorbed onto citrate‐stabilized gold nanoparticles

A systematic study on the surface‐enhanced Raman scattering (SERS) for 3,6‐bi‐2‐pyridyl‐1,2,4,5‐tetrazine (bptz) adsorbed onto citrate‐modified gold nanoparticles (cit‐AuNps) was carried out based on electronic and vibrational spectroscopy and density functional methods. The citrate/bptz exchange was carefully controlled by the stepwise addition of bptz to the cit‐AuNps, inducing flocculation and leading to the rise of a characteristic plasmon coupling band in the visible region. Such stepwise procedure led to a uniform decrease of the citrate SERS signals and to the rise of characteristic peaks of bptz, consistent with surface binding via the N heterocyclic atoms. In contrast, single addition of a large amount of bptz promoted complete aggregation of the nanoparticles, leading to a strong enhancement of the SERS signals. In this case, from the distinct Raman profiles involved, the formation of a new SERS environment became apparent, conjugating the influence of the local hot spots and charge‐transfer (CT) effects. The most strongly enhanced vibrations belong to a₁ and b₂ representations, and were interpreted in terms of the electromagnetic and the CT mechanisms: the latter involving significant contribution of vibronic coupling in the system. Copyright © 2010 John Wiley & Sons, Ltd.     

Calculated polar substituent effects on the stability of 4‐substituted(X) ‐ cub‐1‐yl and ‐bicyclo[2.2.2]oct‐1‐yl cations: a DFT study

The effects of substituents on the stability of 4‐substituted(X) cub‐1‐yl cations ( 2 ), as well as the benchmark 4‐substituted(X) bicyclo[2.2.2]oct‐1‐yl cation systems ( 7 ), for a set of substituents (X = H, NO₂, CN, NC, CF₃, COOH , F, Cl, HO, NH₂, CH₃, SiH₃, Si(CH₃)₃, Li, O^?, and NH) covering a wide range of electronic substituent effects were calculated using the DFT theoretical model at the B3LYP/6‐311 + G(2d,p) level of theory. Linear regression analysis was employed to explore the relationship between the calculated relative hydride affinities (ΔE, kcal/mol) of the appropriate isodesmic reactions for 2 / 7 and polar field/group electronegativity substituent constants (σ_F and σ_χ, respectively). The analysis reveals that the ΔE values of both systems are best described by a combination of both substituent constants. This highlights the distinction between through‐space and through‐bond electronic influences characterized by σ_F and σ_χ, respectively. Copyright © 2010 John Wiley & Sons, Ltd.     

An experimental and theoretical study on the preparation of 4,4′‐methylene‐bis(N,N‐dimethylaniline) in ionic liquid

The reaction of N,N‐dimethylaniline with tetrachloromethane in ionic liquid was found to give 4,4′‐methylene‐bis (N,N‐dimethylaniline) in considerable yield. The ionic liquid was prepared from N,N‐dimethylaniline which is also the one of raw materials for the preparation of 4,4′‐methylene‐bis (N,N‐dimethylaniline), and acts as both solvent and catalyst in the reaction. Mild reaction conditions, enhanced rates, improved yields, and reagents' reactivity which is different from that in conventional organic solvents are the remarkable features observed in ionic liquids. In addition, the results of calculations are in good accordance with the experimental outcomes. Copyright © 2016 John Wiley & Sons, Ltd.     

Thermal reaction of electron deficient 4‐oxo‐4H‐pyrazole 1,2‐dioxide with cycloheptatriene: the first examples of the formation of an endo‐[4π + 6π]‐cycloadduct and an intramolecular 1,3‐dipolar reaction leading to a heterocage

The reaction of 3,5‐bis(methoxycarbonyl)‐4‐oxo‐4H‐pyrazole 1,2‐dioxide (1a) with 1,3,5‐cycloheptatriene (2b) gave a mixture of the novel endo‐[4 + 6]‐cycloadduct (4ab), anti‐exo‐[4 + 2]‐cycloadduct (5ab), and the heterocage (6ab) derived from the intramolecular 1,3‐dipolar cycloaddition reaction of the syn‐endo‐[4 + 2]‐cycloadduct. Analogous endo‐[4 + 6] selectivity in 1,3‐dipolar cycloadditions has not been reported previously. The X‐ray analysis indicates that 6ab has a very long N_sp3–N_sp3 bond distance of 1.617(4) Å. The cycloaddition behaviour is discussed on the basis of transition‐state structures optimized at the B3LYP/6‐31G(d) level of theory, from which predictions of the peri‐, regio‐, and stereoselectivities agreed well with the experimental results. Copyright © 2012 John Wiley & Sons, Ltd.     

Pressure effects on structural,electronic, absorption,and thermodynamic properties of crystalline 2,4,6‐triamino‐3,5‐dinitropyridine‐1‐oxide: A DFT study

Density functional theory calculations have been performed to study the structural, electronic, absorption, and thermodynamic properties of crystalline 2,4,6‐triamino‐3,5‐dinitropyridine‐1‐oxide (TANPyo) in the pressure range of 0–50 GPa. The variation trends of the lattice constants, bond lengths, bond angles, intramolecular H‐bonds, and dihedral angles under compression show that there are two structural transformations at 17 and 38 GPa, respectively. The remarkable changes in the bond lengths indicate that there are two possible initiation decomposition mechanisms of TANPyo under compression. As the pressure increases, the intramolecular H‐bond strengthens. The obvious changes of the dihedral angles show that the planar structure of the TANPyo molecule is damaged under compression. Its absorption spectra show that as the pressure increases, the absorption coefficient of the N–H stretching decreases, while that of the O–H stretching increases. TANPyo has relatively high optical activity at high pressure. An analysis of thermodynamic properties indicates that both two structural transformations are endothermic and not spontaneous at room temperature. Copyright © 2013 John Wiley & Sons, Ltd.     

Synthesis,structural characterization,and spectroscopic properties of the ortho,meta, and para isomers of 8‐(HOCH2‐C6H4)‐BODIPY and 8‐(MeOC6H4)‐BODIPY

Fluorescent members of the 4, 4‐difluoro‐4‐bora‐3a, 4a‐diaza‐s‐indacene (BODIPY) family are widely used for a range of markers, dyes, and sensors. The capacity to substitute the basic framework is an attractive feature permitting a range of differently substituted materials to be formed. New isomeric BODIPYs, o‐, m‐, and p‐8‐[R‐C₆H₄]‐BODIPY (R = CH₂OH, 2a (o), 2b (m), 2c (p); R = OMe, 3a (o), 3b (m), 3c (p)), have been synthesized and characterized by nuclear magnetic resonance, absorbance and emission spectroscopy, and single crystal X‐ray diffraction. The o‐isomers have a very high quantum yield emission in non‐polar solvents, while the m‐ and p‐ analogs showed weak fluorescence under the same conditions. Spectroscopic analysis, as well as X‐ray structural characterization, suggested that substitution in the ortho‐position of the phenyl ring is sufficient to increase the steric hindrance and hence impede the rotation of the phenyl moiety about the 8C‐C axis, thereby favoring radiative compared to non‐radiative relaxation. Copyright © 2013 John Wiley & Sons, Ltd.     

Calculated polar substituent effects on the stability of 3‐substituted(X) bicyclo[1.1.1]pent‐1‐yl cations and 4‐substituted(X) bicyclo[2.2.1]hept‐1‐yl cations: a DFT study

The effects of substituents on the stability of 3‐substituted(X) bicyclo[1.1.1]pent‐1‐yl cations (3) and 4‐substituted(X) bicyclo[2.2.1]hept‐1‐yl cations (4), for a set of substituents (X = H, NO₂, CN, NC, CF₃, CHO, COOH , F, Cl, HO, NH₂, CH₃, SiH₃, Si(CH₃)₃, Li, O^?, and NH₃⁺) covering a wide range of electronic substituent effects were calculated using the DFT theoretical model at the B3LYP/6‐311 + G(2d,p) and B3LYP/6‐31 + G (d) levels of theory, respectively. Linear regression analysis was employed to explore the relationship between the calculated relative hydride affinities (ΔE, kcal/mol) of the appropriate isodesmic reactions for 3/4 and polar field/group electronegativity substituent constants (σ_F and σ_χ, respectively). The analysis reveals that the ΔE values for both systems are best described by a combination of both substituent constants. The result highlights the importance of the σ_χ dependency of charge delocalization in these systems. Copyright © 2012 John Wiley & Sons, Ltd.     

UV filter 2‐ethylhexyl 4‐methoxycinnamate: a structure,energetic and UV–vis spectral analysis based on density functional theory

2‐Ethylhexyl 4‐methoxycinnamate (EHMC) is a very commonly used UVB filter that is known to isomerize from the (E) to the (Z) isomer in the presence of light. In this study, we have performed high level quantum chemical calculations using density functional theory (DFT) with the B3LYP density functional and extended basis sets to study the gas‐phase molecular structure of EHMC and its energetic stability. Calculations were also performed for related smaller molecules cinnamic acid and 4‐methoxycinnamic acid. Charge delocalization has been analyzed using natural charges and Wiberg bond indexes within the natural bond orbital analysis and using nucleus independent chemical shifts. Density functional theory calculations reveal that the (E) isomer of EHMC is more stable than the (Z) by about 20 kJ mol^?1 in both the gas and aqueous phases. The enthalpy of formation in the gas phase of (E)‐EHMC was derived from an isodesmic bond separation reaction. Long‐range corrected DFT calculations in implicit water were made in order to understand the excited state properties of the (E) and (Z) isomers of EHMC. Copyright © 2013 John Wiley & Sons, Ltd.     

The effect of benzo‐annelation on intermolecular hydrogen bond and proton transfer of 2‐methyl‐3‐hydroxy‐4(1H)‐quinolone in methanol: A TD‐DFT study

Excited‐state intermolecular or intramolecular proton transfer (ESIPT) reaction has important potential applications in biological probes. In this paper, the effect of benzo‐annelation on intermolecular hydrogen bond and proton transfer reaction of the 2‐methyl‐3‐hydroxy‐4(1H)‐quinolone (MQ) dye in methanol solvent is investigated by the density functional theory and time‐dependent density functional theory approaches. Both the primary structure parameters and infrared vibrational spectra analysis of MQ and its benzo‐analogue 2‐methyl‐3‐hydroxy‐4(1H)‐benzo‐quinolone (MBQ) show that the intermolecular hydrogen bond O₁―H₂?O₃ significantly strengthens in the excited state, whereas another intermolecular hydrogen bond O₃―H₄?O₅ weakens slightly. Simulated electron absorption and fluorescence spectra are agreement with the experimental data. The noncovalent interaction analysis displays that the intermolecular hydrogen bonds of MQ are obviously stronger than that of MBQ. Additionally, the energy profile analysis via the proton transfer reaction pathway illustrates that the ESIPT reaction of MBQ is relatively harder than that of MQ. Therefore, the effect of benzo‐annelation of the MQ dye weakens the intermolecular hydrogen bond and relatively inhibits the proton transfer reaction.     

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.     

Comparison of SERRS and RRS excitation profiles of [Fe(tpy)2]2+ (tpy = 2,2':6',2'‐terpyridine) supported by DFT calculations: effect of the electrostatic bonding to chloride‐modified Ag nanoparticles on its vibrational and electronic structure

Nonresonance (or normal) Raman scattering (NRS), resonance Raman scattering (RRS), surface‐enhanced Raman scattering (SERS), and surface‐enhanced RRS (SERRS) spectra of [Fe(tpy)₂]²⁺ complex dication (tpy = 2,2':6',2''‐terpyridine) are reported. The comparison of RRS/NRS and SERRS/SERS excitation profiles of [Fe(tpy)₂]²⁺ spectral bands in the range of 445–780 nm is supported by density functional theory (DFT) calculations, Raman depolarization measurements, comparison of the solid [Fe(tpy)₂](SO₄)₂ and solution RRS spectra, and characterization of the Ag nanoparticle (NP) hydrosol/[Fe(tpy)₂]²⁺ SERS/SERRS active system by surface plasmon extinction spectrum and transmission electron microscopy image of the fractal aggregates (D = 1.82). By DFT calculations, both the Raman active modes and the electronic states of the complex have been assigned to the symmetry species of the D_2d point group. It has been demonstrated that upon the electrostatic bonding of the complex dication to the chloride‐modified Ag NPs, the geometric and ground state electronic structure of the complex and the identity of the three different metal‐to‐ligand charge transfer (¹MLCT) electronic transitions remain preserved. On the other hand, the effect of ion pairing manifests itself by a slight change in localization of one of the electronic transitions (with max. at 552 nm) as well as by promotion of the Herzberg–Teller activation of E modes resulting from coupling of E and B₂ excited electronic states. Finally, the very low, 1 × 10⁻¹¹ M SERRS spectral detection limit of [Fe(tpy)₂]²⁺ at 532‐nm excitation is attributed to a concerted action of the electromagnetic and molecular resonance mechanism, in conjunction to the electrostatic bonding of the complex dication to the chloride‐modified Ag NP surface. Copyright © 2014 John Wiley & Sons, Ltd.