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Molecular structure, chemical reactivity, nonlinear optical activity and vibrational spectroscopic studies on 6-(4- n -heptyloxybenzyoloxy)-2-hydroxybenzylidene)amino)-2H-chromen-2-one: A combined density functional theory and experimental approach
Abstract
In this work, we have synthesized new coumarin Schiff base molecule, viz., 6-(4-n-heptyloxybenzyoloxy)-2-hydroxybenzylidene)amino)-2H-chromen-2-one and characterized its structural, electronic and spectroscopic properties experimentally and theoretically. The theoretical analysis of UV–visible absorption spectra reflects a red shift in the absorption maximum in comparison to the experimental results. Most of the vibrational assignments of infrared and Raman spectra predicted using density functional theory approach match well with the experimental findings. Further, the chemical reactivity analysis confirms that solvent highly affects the reactivity of the studied compound. The large hyperpolarizability value of the compound concludes that the system exhibits significant nonlinear optical features and thus, points out their possibility in designing material with high nonlinear activity.
... [9][10][11][12][13] Unlike inorganic materials in which band structure phenomena cause nonlinear phenomena, in organic materials and polymers, these phenomena arise from the transition of an electron from the highest occupied molecular orbital (HOMO) to the lowest unoccupied molecular orbital (LUMO) that caused a transition of the dipole moment from the ground state to the excited state. [14][15][16][17][18] Different types of organic compounds with extensive conjugated π system are expected to exhibit nonlinear optical properties because of π-π interactions that allow an intramolecular charge transfer (ICT). [19][20][21][22][23][24][25][26][27][28][29] Moreover, ICT is responsible for the broadening of the absorption spectrum, and the reduction of the optical bandgap. ...
... 49,50 (13) (14) The first hyperpolarizability (β) , which is studied using second harmonic generation (SHG) is: (15) Also, the direction of charge transfer in the title compound was determined by the ratio of β vec and β total using the following equations: (16) where β vec is the vector component of first hyperpolarizability. 51 (17) The second hyperpolarizability (γ), which is studied using third-harmonic generation (THG) is: (18) The isotropic polarizability (α), the anisotropy of the polarizability (∆α), the vector component of the first hyperpolarizability and hyperpolarizabilities (β, γ) of the title compound are listed in the table 4. unidirectional charge transfer in the title compound. Therefore it is a good candidate for future studies of nonlinear optical properties. ...
In this study, 4-(4,5-Diphenyl-1H-imidazole-2-yl) phenol is successfully synthesized, and its nonlinear optical properties (NLO) are investigated both experimentally and theoretically. Theoretical investigations have been done by using TD-DFT and B3LYP functional with usual 6-31+G(d,p) basis set. The results of HOMO-LUMO and NBO analysis show the low energy gap, high total dipole moment, and hyperpolarizabilities (β, γ) as well as the presence of dipolar excited states with relatively significant dipole-moment changes which are linked to the nonlinearity. The z-scan technique confirmed the NLO properties of title compound. The nonlinear absorption coefficient, refractive index, and third-order susceptibility were found to be 4.044 × 10 −1 cmW −1 , 2.89 × 10 −6 cm 2 W −1 and 2.2627 × 10 −6 esu, respectively. The negative sign of n 2 indicated the occurrence of self-defocusing nonlinearity. The results show that the title compound can been used as potential NLO material.
... The many applications of GQDs as a material can be traced back to the fact that their properties may be designed and manipulated via the manipulation of their structure and components. Chemical potential, chemical hardness, global softness, and the electrophilicity index are all useful chemical reactivity indices for DFT-based studies of reactivity trends, excited states, and toxicity evaluations [43,44]. Koopman's theorem provides a useful framework to evaluate the expressions of the chemical reactivity indices [45][46][47][48][49]. ...
Using density functional theory (DFT), we investigate the structural, stability, and electronic properties of boron nitride (BN) dimers cooped graphene quantum dots (GQDs). A molecule with seven benzene rings and a hydrogen atom at the end of each edge carbon atom (C24H12) as a model for GQDs is used. We assumed that the geometrical arrangement of boron nitride (BN) dimers in GQDs can improve the electronic properties of GQDs. Different positions of B and N atoms are employed to create the three types of BN arrangement, ortho, meta, and para dimers. It has been discovered that the HOMO-LUMO energy gaps of the GQDs structure are significantly affected by the presence of BN dimers. It is noted the energy gap of GQDs changes from − 16.7% to -32.4% by adding BN dimers in different positions, which leads to significant applications. As a result of the value of the electronic gap being around 2.7 eV, these BN dimers can generate an electronic transition for the GQDs system, transforming it from an insulator to a semiconductor. Also, the arrangement of the BN dimers within the GQDs impacts the structural, stabilities, and electronic properties of the nanostructure. These results promote the development of nanodevices with GQDs energetic electronic abilities and improve our knowledge of how chemical doping affects their performance.
... The structural and spectroscopic properties of the substance 6-(4-n-heptyloxybenzyoloxy)− 2-hydroxybenzylidene) amino)− 2H chromen-2-one 5 were investigated both experimentally and theoretically. The first hyper polarizability value in particular, with its huge magnitude, showed its potential application in nonlinear optical devices [43]. ...
... We consider the molecular electrophilicity a better molecular descriptor than chemical potential and hardness because it is a combination of the two, as can be seen in equation 5. Electrophilicity measures a compound's tendency to accept electrons, with lower values indicating higher photostability. [38] The molecular structure with the lowest chemical potential is expected to be the most stable. Hardness indicates a compound's resistance to electron addition or removal, making higher hardness values indicative of greater photostability. ...
Theoretical study of the photophysical/photochemical properties of 1H‐benzimidazole and its derivatives was carried out using APFD, B3LYP, CAM‐B3LYP and PBE0 density functionals with 6‐311+G(2d,p) basis set. The effects of ethanol, 1,4‐dioxane, acetonitrile and water was investigated by means of Integral Equation Formalism of the Polarizable Continuum Model (IEPCM) in the framework of Self‐Consistent Reaction Field (SCRF). The results obtained show that S2 state of the 1H‐benzimidazole molecule is more acidic than the S0 state as the N5−H11 bond length increased to ~ 1.01 Å. At B3LYP/6‐311+G(2d,p) level of theory, the excitation energy of 1H‐bensimidazole molecule in ethanol from S0 to the S2 state was calculated to be 273 nm (4.54 eV). The electronic energy for this transition was calculated to be 0.131 a.u. and observed to occur between π→π* orbitals. Calculations with the PBE0, APFD and B3LYP functionals reproduced the experimental dipole moment in 1,4‐dioxane, with values of 4.09, 4.09 and 4.07 Debye respectively. However, the dipole moments of the 2‐ethyl‐7‐nitro‐5‐substituted‐1H‐benzimidazoles were calculated to be higher for electron donating groups (EDGs) than those bearing electron withdrawing groups (EWGs). In addition, the molecular polarizability was observed to increase with decreasing energy gap. Local excitation (LE) and charge‐transfer (CT) were observed to mediate the mechanisms of electronic excitation in 2‐ethyl‐7‐nitro‐5‐substituted‐1H‐benzimidazoles.
... The MEP predicts electrophilic and nucleophilic sites that combine with nearby molecules [75,76]. The different color codes represent its potential gradient; red signifies the electronegative region, blue and green signify the electropositive region, and the zero potential areas [30]. ...
... The DFT study of the cadmiun(II) complex is performed using M06-2X functional [51] along with 6-311 þ G(d,p) basis set [52] for carbon, oxygen, hydrogen, nitrogen atom and LANL2DZ basis set for cadmium atom as implemented in Gaussian 09 (Rev D.01) package. [53] The gas-phase ground state geometry of the cadmium(II) complex is fully optimized with tight convergence criteria excluding any symmetry constrain. The computed structural parameters of the cadmiun(II) complex evaluated ( [54] of the molecule. ...
2022): A new N 2 O 2-donor compartmental Schiff base ligand and its cadmium(II) complex: synthesis, mesogenic and photoluminescent properties, Inorganic and Nano-Metal Chemistry, A new mesomorphic compartmental [N 2 O 2 ] donor Schiff base ligand [H 2 L] has been synthesized and one corresponding polymeric cadmium(II) complex of the type [Cd-L] n fH 2 L ¼ 4,6-bis((E)-1-(octadecylimino)ethyl) benzene-1,3-diolg is prepared by direct reaction of metal ion with ligand. Both the ligand and its Cd-complex do exhibit mesomorphic properties. The IR spectrum of the lig-and clearly reveals that the ligand acts as a bi-negative tetradentate donor through the two sets of phenolate oxygen and azomethine nitrogen. Mesomorphic behavior of these compounds are investigated with the help of polarizing optical microscopy (POM) and differential scanning calor-imetry (DSC). The organization of the ligand and complex molecules in the mesophase are investigated by X-ray diffraction techniques. The Schiff base ligand and its Cd-complex shows plastic columnar mesophase (Col p) at $82 and $86 C, respectively. The polymeric Cd-complex is blue light emitter with a broad emission maximum at $475 nm on excitation at 380 nm. GRAPHICAL ABSTRACT ARTICLE HISTORY
... The title molecule was created using a method that differed from that described in the literature [23] . The 4NBASA salt was made by dissolving benzenesulfonic acid and p-nitroaniline in methanol in a 1:1 ratio at room temperature. ...
Novel 4-nitrobenzenaminium benzenesulfonate (4NBASA) was synthesized and evaluated using Fourier Transform Infrared (FTIR), 1H and 13C Nuclear Magnetic Resonance (NMR), Ultra-Violet Visible (UV-Vis) spectroscopy, and Single-Crystal X-ray Diffraction (SC-XRD). In addition, theoretical calculations include optimized structure analysis. The (HOMO) high occupied molecular orbital and (LUMO) lowest unoccupied molecular orbital analysis, UV-Vis. parameters with the gas base model, MEP-Molecular Electrostatic Potential, and Non-Linear Optical (NLO) properties were accomplished. All theoretical computations were completed using the DFT/B3LYP functional and the 6-311G++ (d, p) basis set in the ground state. The assignments of estimated infrared vibrational frequencies were accomplished for the first time utilizing the VEDA4 program through the optimized structure, experimental and theoretical data correspond well. In particular, the title compound 4NBASA revealed potent bactericidal activity with maximum of (16.6±1.1mm) at 2.5 µg/mL against Staphlococcus aureus (MTCC 3615) and minimum zone of inhibition of (10.3±0.5mm) on Yersinia enterocolitica (MTCC 840) and also obtained excellent antifungal activity. Further, investigations are warranted to explore their promising NLO properties and other biochemical properties.
... where E N-GQD and E N/X co-doped GQD denote the total energy of the Ndoped and N/X-codoped GQD (X = B, P and S), The possibility of designing and manipulating properties of GQDs by controlling their shape and components has made GQDs one of the most versatile materials. The chemical reactivity parameters [45][46][47][48], such as chemical hardness η [49], chemical potential μ [50] and electrophilicity index ω [51,52], are very useful to study reactivity trend, excited states and analyzing toxicity [53,54]. The quantitative definitions for chemical potential and chemical hardness can respectively be given as: Table 1 The chemical formula, cohesive energy E c , chemical hardness η, chemical potential μ and electrophilicity index ω of doped GQDs with different heteroatom doped patterns. ...
Heteroatom doping, especially co-doping, is an effective way to tailor electronic structures of graphene quantum dots (GQDs) with synergistic effects and desirable properties. However, due to different synthesis methods, the widespread use of GQDs co-doped with heteroatoms is hindered by the poor understanding of their optical properties and mechanisms. In this work, co-doped GQDs based on three N-doping configurations are chosen to reveal underlying mechanisms of optical properties using density functional theory and time-dependent density functional theory calculations. Based on different N-doping patterns, B, P and S atoms can endow GQDs with a wide spectrum of new optical properties and electronic structures. The HOMO–LUMO gaps of N-doped GQDs with graphitic N, pyrrolic N, and pyridinic N are 0.77, 0.25 and 2.69 eV, respectively. In the co-doped GQDs, B, P and S containing functional groups cause low absorptions in the range of 400 to 800 nm and multiple absorption peaks at about 400 and 600 nm, while the N atom affects the position and intensity of prominent absorption peak according to three different N-doping patterns. The B atom forms sp² hybridization in the graphene lattice, while the P and S atoms transform the sp² hybridized carbon into the sp³ state. It is anticipated that this work will provide valuable insights for understanding absorption mechanisms and electronic properties of heteroatom co-doped GQDs as well as achieving new applications with well-defined and desired properties.
... Green indicates the neutral electrostatic potential region. 39 ESP maps (using CAM-B3LYP function) of all the epoxies and hardeners are shown in Table 2. Almost all of oxygen atoms are on a level of lower potential. The oxygen atom of isosorbide epoxy has a highest electronic density followed by CHDM. ...
Non-planar-ring epoxies together with non-planar-ring hardeners could achieve thermosets combining ultra-high shape recovery speed and excellent thermal properties. High shape recovery speed reflected high efficiency, and could decrease the energy consumption and the harmful effect of external stimuli on the materials, while it often conflicts with the thermal properties of shape memory polymers. In this paper, for the first time, epoxy resins with the super-short shape recovery time within 3 s were developed from non-planar-ring epoxies and hardeners, and their glass transition temperature (Tg) were ∼127 °C much higher than their benzene ring analogues. The effects of non-planar-ring structures of the epoxies and hardeners on the curing behavior, thermal properties as well as the shape memory properties of the thermosets were systematically investigated; the structure-property relationships were disclosed with the help of computational simulation of structure parameters and ESP maps. The faster shape recovery speed of the non-planar-ring epoxy thermosets is from their higher molecular mobility contributed by the conformational transition of non-planar-rings as well as their higher recovery force compared with benzene ring analogs. Their higher Tgs are from the steric hindrance by the larger molecular volume of the non-planar-rings than benzene ring. This work will provide an effective method to produce shape memory polymers with excellent shape memory effects and high performance.
... The nonlinear optical property of a material is mainly characterized by large hyperpolarizability (β) value. The basic requirement for having large β value is that the structure should be non-centrosymmetric in nature [15] and have a large number of π-electrons. Graphyne possesses this type of geometry and for this reason, we have chosen graphyne system in our present study to investigate the non-linear optical response. ...
The change in electronic and nonlinear optical properties of pristine graphyne due to the substitution of hydrogen atom by donor-acceptor groups (by varying the position and concentration of donor-acceptor group) have been investigated with the help of density functional theory approach employing the cam-b3lyp/6-311+g(d,p) level of theory. This conjugated framework exhibits enormous improvement in first order hyperpolarizability (both static and dynamic) than that of their pristine counterpart and thus they demand as a potential candidate for designing high quality nonlinear optical materials.
The current study has obtained excellent potential nonlinear optical(NLO) materials by combining density functional theory methods with sum-over-states model to predict the second order NLO properties of helical graphene nanoribbons(HGNs) through introducing azulene defects or/and BN units. The introduction of these functional groups deforms the pristine HGN (compression or tension) and enhances obviously the static first hyperpolarizability(〈β0〉) of system by up to two orders of magnitude. The tensor components along the helical axis of HGNs play a dominant role in the total 〈β0〉. The azulene defects and the BN units polarize the pristine HGN to different degrees, and the azulenes and contiguous benzenes are involved in the major electron excitations with significant contributions to 〈β0〉 but the BN units are not. The BN-doped chiral HGNs have good kinetic stability and strong second order NLO properties(6.84 × 105 × 10−30 esu), and can be a potential candidate of high-performance second order NLO materials. The predicted two-dimensional second order NLO spectra provide useful information for further exploration of those helicenes for electro-optic applications.
Optical properties of N- and F-doping triangular-shaped carbon molecules have been investigated in theory and experiment. The theoretical results showed that carbon molecules with impurity F and Cl have the same characters with pure carbon. Doping N into pure carbon molecule would change the optical rotation at 589 nm. For doping N replacing hydrogen atom structures (N-doping 1 and N-doping 2 molecules), the absorption spectra of them are similar to pure carbon molecule. However, for molecules with impurity N atom in benzene ring (N-doping 3 and N-doping 4 molecules), the peaks of wavelength of absorption spectra shift to long wavelength compared to that of pure carbon molecule. Moreover, the delocalization of molecular orbital (MO) is different from pure carbon molecule, which is caused by the impurity N changing the electrons distribution of benzene ring. We have calculated 3 without H and 4 without H molecules which are removing hydrogen atom in nitrogen atom from N-doping 3 and 4. 3 without H and 4 without H molecules have similar optical properties with pure carbon molecule. The results testified that the impurity N and F would not change the optical properties of carbon molecule if impurity did not change the delocalization of all benzene rings.Graphical abstract
Optical properties of nitrogen- and fluorine-doping carbon molecules investigating in theory and experiment.
In this work, azulene is introduced into nano-graphene with coronene center to enhance the second-order nonlinear optical (NLO) properties. The sum-over-states(SOS) model based calculations demonstrate that dipolar contributions are larger than octupolar contributions to the static first hyperpolarizability(〈β0〉) in most nano-graphenes except those with high symmetry(e.g., a C2v nano-graphene has octupolar contributions ΦJ=3 up to 59.0% of the 〈β0〉). Nano-graphenes containing two parallel orientating azulenes (i.e., Out-P and Out-Ps) have large dipole moments, while their ground state is triplet. Introducing B/N/BN atoms into the positions with a high spin density transfers the ground state of Out-P and Out-Ps to closed-shell singlet, and the Out-Ps-2N has a large 〈β0〉 of 1621.67×10−30 esu. Further addition of an electron donor(NH2) at the pentagon end enhances the 〈β0〉 to 1906.22×10−30 esu. The two-dimensional second-order NLO spectra predicted by using the SOS model find strong sum frequency generations and difference frequency generations, especially in the near-infrared and visible regions. The strategies to stabilize the electronic structure and improve the NLO properties of azulene-defect carbon nanomaterials are proposed, and those strategies to engineer nano-graphenes to be semiconducting while maintaining the π-framework are extendable to other similar systems.
Zinc oxide nanosheet (ZnONS) is a promising road to deliver numerous anticancer drugs (5-FU, 6-MP, GB, and CP) in the human body. The electronic properties of the anticancer drugs/ZnONS studied by using DFT method, which implemented in the quantum espresso package. Our finding shown that ZnONS has a semiconductor behavior. Interestingly, the electronic band gap of the 5-FU/ZnONS and GB/ZnONS is decreased, but they still have semiconductor behaviors. For 6-MP/ZnONS, it is increased and converted to n-type semiconductor for CP/ZnONS structure. According to acquired findings, the complex structures became more stable and lower reactive due to the total energy of these complex structures is increased compared to pristine ZnONS. All complex structures are required higher excitation energy to transfer an electron due to the chemical hardness of all complex structures is decreased, but the 6-MP/ZnONS structure has the opposite behavior. There is a weak interaction between ZnONS and (5-FU, 6-MP, and GB) and good interaction between the ZnONS and CP due to the electrophilic of these structures has lower and higher values, respectively. Concisely, ZnONS considered the greatest substrate to carry all these anticancer drugs.
Spectroscopic analysis and different quantum mechanical studies of four phramaceutically active flavanoid compounds, 5,7-dihydroxy-3-(4-hydroxyphenyl)-4H-chromen-4-one (genistein) (F1), 5,7-dihydroxy-2-(4-hydroxyphenyl)-4H-chromen-4-one (apigenin) (F2), 5,6,7-trihydroxy-2-phenyl-4H-chromen-4-one (baicalein) (F3) and 2-(3,4-dihydroxyphenyl)-3,7-dihydroxy-4H-chromen-4-one (fisetin) (F4) are reported in this manuscript using DFT/B3LYP/6-311++G(d,p) level of theory. Simulated IR spectrum of these compounds was compared with experimentally available data, and essential functional group assignments were made. NBO studies helped to study the various intramolecular electron delocalisation possible in the molecule. We also report the frontier orbital properties and other derived local energy descriptors which talks about the relative stability and reactivity of the compounds. The photovoltaic efficiency of the compounds was studied from the simulated electronic spectra. The compound was found to interact with graphene, to form molecular self-assembly. These self-assemblies showed tremendous enhancement in various physicochemical properties when compared with its constituents. Biological activity of the compounds were predicted using molecular docking studies.
Bridging group is an indispensable element for the preparation of diphenol-based benzoxazines, and inevitably, it’s electronic features will affect the H-bonds formation of obtained benzoxazine, which is a crucial factor that not only makes a difference on curing behaviors of benzoxazine, but also poses significant influence on the performances of cured resins. However, systematical investigation about the effects of bridging group on the H-bonds in benzoxazine is still in a barren state. Herein, we bridge the gap with three high purity model benzoxazine monomers. The results showed that electron-donating bridge groups made the benzoxazine monomers tend to start curing reaction earlier, whereas the electron-withdrawing bridging groups had the opposite effect. In addition, it was also confirmed that the H-bonds in polybenzoxazine could be readily tailored by carefully selecting the bridge groups of aromatic diphenols. In this work, some basic characteristics about benzoxazine have been revealed, which is helpful for us to understand its structure-properties relationship more deeply.
Organic compounds based on ferrocene, pyrazolole and octahydroacridine exhibit high interest due to their unusual structure, with potential practical applications due to their special optical properties. Nonlinear optical properties of some new synthesized derivatives are evaluated in relationship with the chemical structure by using DFT molecular modeling.
In condensed state ferrocene and other organic molecules were found in a staggered arrangement(D5d) as non-polar molecule, but the eclipsed (D5h) and twisted (D5) forms exhibit SHG capabilities. The molecular polarizability (α), first order hyperpolarizabilities (βtot,), dipole (μtot) and quadrupole (Q) moments, were computed. The NLO efficiency was assessed by the relationship between high (βtot,) and low HOMO-LUMO energy gap.
The nonlinear optical properties of some new synthesized compounds were evaluated in thin films with nanometric morphology obtained using various methods: Langmuir Blodgett thin films, sol-gel deposition, layer by layer deposition.
Keywords: nonlinear optics, thin films, nanostructures, hybrid materials, Langmuir Blodgett film, layer-by-layer.
The present study emphasizes on structural, opto-electronic, vibrational and non-linear properties, at electronic structure level, on 4-fluoro-4-hydoxybenzophenone molecule using the first principle calculation. Detailed vibrational assignments of the wavenumbers are carried out on the basis of potential energy distribution and a good agreement between the reported and calculated wavenumber has been observed. Further, molecular electrostatic potential surface predicts the reactive site of the molecule. From the time dependent density functional theory analysis on UV-visible spectra, a red shift has been observed on maximum absorption wavelength when gaseous medium is replaced by solvent medium. The nonlinear optical property of the 4-fluoro-4-hydroxybenzophenone molecule shows that this molecule possesses large nonlinear optical properties which might make it useful for various nonlinear optical applications.
In the present study, as a result of detailed conformational search of
the 7-Ethoxycoumarin, four different conformers of (7EC) have been
obtained. The FT-IR and Raman spectra of 7EC were recorded in the region
4000-400 cm-1 and 3500-50 cm-1, respectively.
Vibrational frequences of the title compound were calculated by B3LYP
method using 6-311++G(d,p) basis sets. The calculated vibrational
frequences were analyzed and compared with experimental results.
Characteristic vibrational bands of the pyrone ring, methylene and CO
groups have been identified.
6-Amino coumarin has been established as an efficient nitrite ion selective fluorescent sensor. The developed method shows linearity up to 1.6 × 10 mol L of nitrite ion concentration. Interference from other common anions is almost negligible. The reagent shows strong binding affinity towards nitrite ion as evident from its binding constant value (5.8 × 10), estimated by Stern-Volmer method. Some real samples were analyzed. Single crystal X-ray structure of the reagent is reported. Preliminary computational studies on the molecular level interaction between the reagent and nitrite ion were performed by density functional theory (DFT, B3LYP) method.
A coumarin-based Schiff base (receptor ) exhibited fluorescence enhancement selectively with Zn(2+) at a nanomolar level in near-aqueous medium (EtOH-H2O; 1 : 1, v/v). The response was instantaneous with a detection limit of 3.26 × 10(-9) M. The sensing event is supposed to incorporate a combinational effect of intramolecular charge transfer (ICT), chelation-enhanced fluorescence (CHEF) and C[double bond, length as m-dash]N isomerization mechanisms. Various spectroscopic methods, viz. IR, UV-visible, fluorescence and NMR in association with single crystal XRD studies, were used for thorough investigation of the structure of receptor as well as of the sensing event. The Zn(2+) complex of receptor exhibited a very nice 1D chain coordination polymeric framework in its single crystal XRD.
Rare-earth complexes of mesomorphicSchiff's bases, 4-[(alkylimino)methyl]-3-hydroxyphenyl-4- alkyloxybenzoates, were synthesized. Whereas the ligands LH display a nematic and/or a smectic C phase, the metal complexes show a viscous smectic A phase and decompose at the clearing point. The mesophase was investigated by hot-stage polarizing optical microscopy, by differential scanning calorimetry and by high temperature X-ray diffraction. Two types of complex were found, [Ln(LH)(3)(NO3)(3)] and [Ln(LH)(2)L(NO3)(2)], depending on the ligand or the central metal ion. The first coordination sphere of the rare-earth ion in these metallomesogens is comparable to that in the structure of complexes with 4- alkoxy-N-alkyl-2-hydroxybenzaldimine ligands
We present two new hybrid meta exchange- correlation functionals, called M06 and M06-2X. The M06 functional is parametrized
including both transition metals and nonmetals, whereas the M06-2X functional is a high-nonlocality functional with double
the amount of nonlocal exchange (2X), and it is parametrized only for nonmetals.The functionals, along with the previously
published M06-L local functional and the M06-HF full-Hartree–Fock functionals, constitute the M06 suite of complementary functionals.
We assess these four functionals by comparing their performance to that of 12 other functionals and Hartree–Fock theory for
403 energetic data in 29 diverse databases, including ten databases for thermochemistry, four databases for kinetics, eight
databases for noncovalent interactions, three databases for transition metal bonding, one database for metal atom excitation
energies, and three databases for molecular excitation energies. We also illustrate the performance of these 17 methods for
three databases containing 40 bond lengths and for databases containing 38 vibrational frequencies and 15 vibrational zero
point energies. We recommend the M06-2X functional for applications involving main-group thermochemistry, kinetics, noncovalent
interactions, and electronic excitation energies to valence and Rydberg states. We recommend the M06 functional for application
in organometallic and inorganometallic chemistry and for noncovalent interactions.
A novel Near Infra-Red emitting BODIPY derivative is presented which exhibits the largest Stokes shift thus far reported for a BODIPY compound.
An amorphous polymer bearing a number of H-bonded coumarin groups can display large bending towards incident UV light. Imbalanced surface stresses generated by the photocrosslinking of polymer chains occurring on the side of the film receiving the UV light are believed to cause the photoinduced deformation.
New hockey-stick-shaped 2,5-diphenyl-1,3,4-thiadiazole-containing mesogens have been designed and synthesised. These molecules possess 4-n-alkoxy chain at the elongated arm whereas and 4-n-butyloxy chain at the shorter arm of the molecule. The compounds are fluorescent and emission located in the violet to blue region with a large stoke shift observed in polar solvents. No substantial solvatochromic effect was found in the absorption maxima, but in the emission, a red shift was observed with increasing the solvent polarity. In the solid thin film, compounds emitted green light. The compounds having longer chain (n > 8) exhibit SmA and SmC phase, while the compounds with shorter chain at one end of the molecule display nematic and SmC phase. The density functional theory study has been carried out to investigate the stable configuration and the influence of solvent on bond length, bond angle, bending angle, dipole moment, polarisability of the molecule. It also enables us to predict the possible reactive sites and effect of solvent on the chemical reactivity descriptors. Our study concludes that the molecule becomes more reactive in solvent compared to gas. The large voltage holding ratio confirms that this molecule may be used for active matrix display applications.
The hard / soft acids / bases principle has been justifiably criticized because of the lack of a precise definition of hardness and the inability to quantify this property; recent developments have overcome these objections, however. Keywords (Audience): Second-Year UndergraduateKeywords (Domain): Inorganic ChemistryKeywords (Subject): Acids / Bases
By condensing 2‐aminobenzothiazole with 2‐hydroxy‐1‐naphthaldehyde, 2‐hydroxybenzaldehyde, 4‐methoxybenzaldehyde, 4‐hydroxybenzal‐dehyde, benzaldehyde and 4‐dimethylaminobenzaldehyde, and five Schiff bases Ia‐Ie are prepared. Also, two Schiff bases IIa and IIb are prepared by condensation of 2‐amino‐3‐hydroxypyridine with 2‐hydroxy‐1‐naphthaldehyde and 2‐hydroxybenzaldehyde. The ¹ H NMR, IR and UV/Vis spectra of these seven Schiff bases are investigated. The signals of the ¹ H NMR spectra as well as the important bands in the IR spectra are considered and discussed in relation to molecular structure. The UV/Vis absorption bands in ethanol are assigned to the corresponding electronic transitions and the electronic absorption spectra of Schiff bases Ib and IIb are studied in organic solvents of different polarities. The UV/Vis absorption spectra of 2‐amino‐3‐hydroxypyridine Schiff bases IIa and IIb are investigated in buffer solutions of different pH values containing 5% (v/v) methanol, and the results are utilized for the determination of pK a and ΔG * of the ionization of the phenolic OH‐groups. The fluorescence spectra of IIa and IIb are studied in organic solvents of different polarities.
The obtained spectral results are confirmed by some molecular calculations using the atom super position and electron delocalization molecular orbital theory for the Schiff base IIb.
A new coumarin-derived fluorescent probe (1) exhibited significant fluorescence quenching in the presence of Cu2+ ions. Other metal ions, e.g. Ag+, Ca2+, Cd2+, Co2+, Fe2+, Fe3+, Hg2+, K+, Mg2+, Mn2+, Ni2+, Pb2+, and Zn2+, produced only minor changes in the fluorescence of chemosensor 1. The binding ratio of the chemosensor-Cu2+ complexes was found to be 2:1, according to Job plot experiments. The association constant (Ka) for Cu2+ binding with chemosensor 1 was found to be 9.56 x 109 M-2. The maximum fluorescence quenching caused by Cu2+ binding with chemosensor 1 occurred over a pH range of 5–9. Moreover, fluorescence microscopy experiments showed that chemosensor 1 could be used as a fluorescent probe for detecting Cu2+ in living cells.
The large volume of research related to supramolecular π-gel chemistry indicates the potential of this area in the field of new functional materials useful for a variety of application, particularly to the fabrication of organic electronic devices. For improved electronic properties, it is necessary to avoid/reduce the content of insulating alkyl chains in the gelator molecules, which is the key point in balancing solubility and precipitation. This will improve the 1D ordering of the gelator and thereby the charge transport properties. Postpolymerization approaches and hybrid material assemblies of gels should be further explored to obtain stable structures that can overcome ambient conditions without loosing the electronic properties. π-gelators have great potential to the development of self-assembly based bulk heterojunction solar cells. For improved performance in this field, more appropriate D-A systems with absorption characteristics extendable to the near-IR and IR regions of the electromagnetic spectrum for more solar radiation coverage, improved stability and environmental compatibility are needed.
Precision is given to the concept of electronegativity. It is the negative of the chemical potential (the Lagrange multiplier for the normalization constraint) in the Hohenberg–Kohn density functional theory of the ground state: χ=−μ=−(∂E/∂N)v. Electronegativity is constant throughout an atom or molecule, and constant from orbital to orbital within an atom or molecule. Definitions are given of the concepts of an atom in a molecule and of a valence state of an atom in a molecule, and it is shown how valence‐state electronegativity differences drive charge transfers on molecule formation. An equation of Gibbs–Duhem type is given for the change of electronegativity from one situation to another, and some discussion is given of certain relations among energy components discovered by Fraga.
In the present study, an exhaustive conformational search of the (triphenylphosphoranylidene) acetaldehyde has been performed. The FT-IR spectrum of this compound was recorded in the region 4000–400 cm−1. The FT-Raman spectrum was also recorded in the region 3500–50 cm−1. Vibrational frequencies of the title compound have been calculated by B3LYP method using 6-311++G(d,p) basis sets. The calculated geometric parameters and vibrational frequencies were analyzed and compared with obtained experimental results.
In the past decades the development of photorefractive devices evolved rapidly as can be seen by the increasing number of publications and numerous applications. There is still need of innovative materials which are suitable for a broad range of applications through tailored properties. We present photorefractive linear and crosslinked polysiloxanes with refractive indices of up to n = 1.603 which may be tuned in their refractive index in a range of up to Δn = 0.04 photochemically. The polysiloxanes, more commonly named silicones, have side chains containing coumarin which are attached to the polymer backbone via different spacers ranging in length from 3 to 9 methyl groups. The coumarins undergo wavelength-dependent photodimerization and photocleavage in the polymer which cause the desired refractive index changes. The polysiloxanes have low glass transition temperatures ranging from −2 °C to 35 °C and show a high thermal stability (T5% > 410 °C). These properties make these materials promising candidates for the manufacture of photo tunable polymers, e.g. for the use as optical data storage materials, alignment of liquid crystals, and photorefractive intraocular lenses.
The CN stretching frequency in seventeen substituted salicylidene aniline—copper (II) complexes is assigned both in the solid state and in solution. In Nujol mulls, the CN stretching frequency is found at 1603–1616 cm−1, while in methylene chloride solution, the band is shifted slightly to 1602–1612 cm−1. In the copper (II) complexes, the phenolic CO appears in the region 1310–1330 cm−1 as compared to 1265–1288 cm−1 in the free anils.
FT-Raman and FT-IR spectra of the 7-aminoflavone have been recorded and analysed. The detailed interpretation of the vibrational spectra has been carried out with the aid of normal coordinate analysis following the scaled quantum mechanical force field methodology. The various intramolecular interactions that are responsible for stabilisation of the molecule were revealed by natural bond orbital analysis. The obtained vibrational wavenumbers and optimised geometric parameters were observed to be in good agreement with the experimental data. The carbonyl stretching vibrations have been lowered due to conjugation and hydrogen bonding in the molecules.
Gaussian-2 (G2) theory has been extended to molecules containing the third-row nontransition elements Ga–Kr. Basis sets compatible with those used in G2 theory for molecules containing first- and second-row atoms have been derived. Spin–orbit corrections for atoms and molecules having spatially degenerate states (2P, 3P for atoms and 2&Pgr; for molecules in this work) are included explicitly in the G2 energies. The average absolute deviation from experiment for 40 test reactions is 1.37 kcal/mol. In contrast to the situation for first- and second-row molecules, inclusion of spin–orbit effects is very important in attaining accurate energies for molecules containing third-row atoms. Without spin–orbit effects, the average absolute deviation is 2.36 kcal/mol.
This chapter discusses the chemical reactivity dynamics in ground and excited electronic states. Quantum fluid density functional theory (DFT) is employed to study a chemical reaction mimicked as a collision process between an ion and an atom in its ground and excited electronic states as well as the interaction of the atom with an external laser field, and to monitor the time evolution of various reactivity parameters to gain insights into the related structure principles in a dynamical context, involving ground as well as excited states. The basic aspects of quantum fluid DFT is introduced followed by the analysis of the nature of the chemical reactivity in the excited states. The chapter also describes ion–atom collision, atom–field interaction processes, chaotic ionization, and regioselectivity.
We report the synthesis of the Schiff base ligands, 4-[(4-bromo-phenylimino)-methyl]-benzene-1,2,3-triol (A1), 4-[(3,5-di-tert-butyl-4-hydroxy-phenylimino)-methyl]-benzene-1,2,3-triol (A2), 3-(p-tolylimino-methyl)-benzene-1,2-diol (A3), 3-[(4-bromo-phenylimino)-methyl]-benzene-1,2-diol (A4), and 4-[(3,5-di-tert-butyl-4-hydroxy-phenylimino)-methyl]-benzene-1,3-diol (A5), and their Cd(II) and Cu(II) metal complexes, stability constants and potentiometric studies. The structure of the ligands and their complexes was investigated using elemental analysis, FT-IR, UV–Vis, 1H and 13C NMR, mass spectra, magnetic susceptibility and conductance measurements. In the complexes, all the ligands behave as bidentate ligands, the oxygen in the ortho position and azomethine nitrogen atoms of the ligands coordinate to the metal ions. The keto-enol tautomeric forms of the Schiff base ligands A1–A5 have been investigated in polar and non-polar organic solvents. Antimicrobial activity of the ligands and metal complexes were tested using the disc diffusion method and the strains Bacillus megaterium and Candida tropicalis.
The electronic absorption spectra of coumarin and its derivatives umbelliferone (6-hydroxycoumarin), esculetin (6,7-dihydroxycoumarin), and scopoletin (6-methoxy-7-hydroxycoumarin) were investigated. The n → π* transition was not observed in the spectrum of coumarin but was observed in the spectra of some of its derivatives. Molecular orbital calculations, using the INDO procedures, were carried out on coumarin and some of its derivatives. The activities of the different sites of the molecules are discussed in terms of the coefficients of the atomic orbitals constituting the HOMO and the LUMO. The correspondence between the calculated and experimental transition energy and band intensity is satisfactory.
Variation of global reactivity descriptors along the two different pathways for formaldehyde decomposition has been investigated in order to analyze the validity of various electronic structure principles of density functional theory. Calculated energetics and geometrical parameters are in good agreement with the previous investigations. The hardness and electrophilicity are, respectively, found to be a pointer of the most stable and the most reactive identity in most cases. Profiles of these quantities, as a function of the reaction coordinates narrate the dependability of the descriptors. The difference in the global reactivity descriptors between a symmetric reaction and a non-symmetrical reaction along the reaction coordinate in the same decomposition pathway has also been analyzed. Our investigation provides useful exploratory guidelines towards the foundation of chemical reactivity descriptors.
The charge transfer and joint hardness between benzidine, 3,3′-dimethoxybenzidine, 3,3′-dichlorobenzidine, 2,2′,5,5′-tetrachlorobiphenyl, 3,3′,4,4′,5,-pentachlorobiphenyl and dibenzofuran with nucleic acid bases such as adenine, thymine, guanine, cytosine, uracil, and base pairs like GCWC and ATH are investigated. It has been shown that benzidines act as electron donors whereas polychlorinated biphenyls and dibenzofuran act as electron acceptors during their interaction with biomolecular environments. Further, experimental biological activities (pIC50) of polychlorinated dibenzofurans (PCDF) are correlated with their corresponding activity (pIC50 values) calculated using the electrophilicity index and the local electrophilic power through regression analysis from different population analysis schemes like MPA, NPA and HPA. A good correlation is obtained showing the significance of the selected descriptors in quantitative structure toxicity prediction.
The second-order nonlinear optical properties of photocross-linkable coumarin-based copolymers were investigated using the optical second harmonic generation (SHG) with the Maker fringes technique. High quality and transparent spin-deposited thin films of various methacrylic copolymers containing 4-methylcoumarin pendant chromophores were prepared and the coumarin units were ordered and oriented by the corona poling technique. Nonlinear optical investigations were performed using a picosecond Q-witched Nd:YAG laser working at the fundamental wavelength (k= 1064 nm) and the second order nonlinear optical susceptibilities of the functionalized polymers were determined. The samples were irradi-ated using two wavelengths (k= 254 nm and k> 300 nm) promoting the reversible photo-induced dimerisation of coumarin moieties within the film. The latter is shown to have a significant impact on
the nonlinear optical response of the corresponding material. A large SHG response of photocross-link-able coumarin-based copolymers is obtained.
Star-shaped molecules consisting of a 1,3,4-oxadiazole core derivatized with alkoxy-substituted phenyl ethynylenes, FD12 (dodecyl) and FD16 (hexadecyl) were synthesized. These molecules exhibited enantiotropic columnar mesophases over a wide temperature range, with the liquid crystalline phases exhibiting strong blue fluorescence. On cooling, FD12 transformed into a transparent glass at room temperature wherein the liquid crystalline texture was retained. The glassy film remained stable over a period of one year and exhibited blue luminescence with an absolute quantum yield of 26%. The oxadiazole derivatives formed stable luminescent gels in decane and study of their morphology by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) indicated formation of interlocked network of self-assembled fibers. X-ray diffraction (XRD) analysis of the xerogel of these derivatives indicated oblique columnar ordering of the molecules within the fibers. The length of the alkyl substituent was observed to have a significant effect on the absorption and fluorescence properties of the gels, which was attributable to the role of the alkyl substituents in controlling the nature of the molecular packing within the self -assembled fibers of the gels.
Polymers containing 6- and 7-substituted coumarin moieties were prepared as photoalignment films through linearly polarized UV irradiation to a varying fluence for an investigation of liquid crystal orientation. Model coumarin monomers and dimers were also synthesized and characterized as part of a novel approach to the interpretation of liquid crystal orientation in terms of monomer conversion. The experimental results for monomer conversion as a function of fluence were used to validate the first-order kinetics with an exponentially decaying rate constant as the reaction proceeds. A kinetic model was constructed to describe the evolutions of the orientational order on the parts of the reacted and the unreacted coumarin moieties. The model was instrumental to the visualization of liquid crystal orientation on photoalignment films at the early and the late stages of dimerization. Furthermore, the observed crossover in liquid crystal orientation on the polymer film comprising 7-substituted coumarin moieties was successfully interpreted by considering three factors: the relative abundance of the reacted and the unreacted coumarin moieties, the degrees of their orientational order predicted by the kinetic model, and the energetics of molecular interaction.
A generalized concept of philicity is introduced through a resolution of identity, encompassing electrophilic, nucleophilic, and radial reactions. Locally, a particular molecular site may be more prone to electrophilic attack or another may be more prone to nucleophilic attack, but the overall philicity of the whole molecule remains conserved. Local philicity is by far the most powerful concept of reactivity and selectivity when compared to the global electrophilicity index, Fukui function, local softness, or global softness because it contains information about almost all of the known global and local descriptors of chemical reactivity and selectivity.
The intramolecular hydrogen bonding in o-hydroxy aromatic Schiff bases has been investigated. This has permitted the direct physical determination of Hammett σ-constants of ortho, as well as meta and para substituents. The ortho values are found to be similar to the para values.
Principles of minimum energy, minimum polarizability, minimum electrophilicity, and maximum hardness dictate that the aromatic molecules are associated with low energy, low polarizability, low electrophilicity, and high hardness values. The antiaromatic molecules should possess high energy, high polarizability, high electrophilicity, and low hardness values. This fact is demonstrated through the B3LYP/6-311G** calculations on benzene and cyclobutadiene. Aromaticity in aluminum clusters is also analyzed. Keywords (Audience): Second-Year Undergraduate
Some coumarin-based fluorophores were synthesized and characterized by elemental analysis, (1)H NMR, (13)C NMR and MS. The solid-state photoluminescence properties were studied. The benzocoumarins display interesting solid-state emission properties with an emission at wavelengths ranging from 532 to 645 nm, when excited by a 325 nm helium-cadmium laser at room temperature. The results demonstrated that the luminescent colors can be tuned from green to red by simply varying molecular structure. The benzocoumarin-phenyl boronic acid hybrid, 4-(3-oxo-3-(2 -oxo-2H-1-naphtho[2,1-b]pyran-3-yl)-prop-1-enyl)phenyl boronic acid, showed obvious fluorescence response to water. Whereas the free compound was very weakly fluorescent in tetrahydrofuran (THF), the addition of water leads to an appearance of strong blue-green fluorescence and a dramatic increase of emission intensity. Besides, 3-(3-(3,4,5-trimethoxyphenyl)-prop-2-enoyl)-2H-1-benzopyran-2-one exhibited second order nonlinear optical response to laser pulses. A noticeable second harmonic generation (SHG) under pulsed excitation at 1064 nm was observed. Preliminary nonlinear measurements on powder samples showed that the second harmonic generation efficiency is roughly 5.8 times that of potassium dihydrogen phosphate (KDP).
The vibrational and electronic spectra of 3-cyano-4-methylcoumarin (3C4MC) are reported and discussed. In this work the structural properties, vibrational frequencies and electronic spectra of 3C4MC have been investigated extensively using density functional theory (DFT) employing B3LYP exchange correlation with the normal basis level 6-31G(d,p). NBO and HOMO, LUMO analysis has been carried out. The geometries and normal modes of vibrations obtained from B3LYP calculations are in good agreement with the experimentally observed data.
The fundamental principles of density functional theory are applied to achieve a better understanding of Various theoretical tools for describing chemical reactivity. Emphasis is given to the Fukui function, the central site restetivity index of density functional theory, which is approached through its own variational principle. A maximum hardness principle is then developed and discussed. To make contact with an earlier proof of a maximum hardness principle, changes in chemical potential are considered.
An attempt has been made to test the usefulness of the generalized philicity concept of Chattaraj et al. through gas- and solution-phase density functional theory calculations on some aliphatic amines. Local philicity provides important clues about the reactivity and selectivity, and it contains almost all the known global and local chemical reactivity parameters. Local philicity provides the Fukui function, but the converse is not true. We have also studied the effect of solvent (water) on reactivity. The philicities are in general less in solvent than in the gas phase, but the total energy and dipole moment are higher in the solvent medium. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2005
We synthesized a series of polystyrene derivatives containing coumarin side groups using polymer analogous reactions. The liquid‐crystal (LC) alignment director for these polymer films was found to be perpendicular to the rubbing direction. The contrast ratio and anchoring‐energy values of these polystyrene derivatives were found to be much greater than those of polystyrene and poly(chloromethylstyrene), indicating that the coumarin side groups increase the aligning ability. For example, the anchoring energy of a polymer with 82 mol‐% of coumarin‐containing monomeric units, compared to polystyrene, is about 7 × 10 ⁻⁵ J · m ⁻² and 1 × 10 ⁻⁷ J · m ⁻² , respectively.
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Coumarin-based chromophores with azo and pyrazoline moieties were synthesized and their structures and properties elucidated using spectroscopy. The coumarins were luminescent, having solid state emission at wavelengths ranging from 400 to 750 nm, depending on structure. The relationships between the solid state photoluminescence and both chemical and crystal structures are discussed.
Optimized scale factors for calculating vibrational harmonic and fundamental frequencies and zero-point energies have been determined for 145 electronic model chemistries, including 119 based on approximate functionals depending on occupied orbitals, 19 based on single-level wave function theory, three based on the neglect-of-diatomic-differential-overlap, two based on doubly hybrid density functional theory, and two based on multicoefficient correlation methods. Forty of the scale factors are obtained from large databases, which are also used to derive two universal scale factor ratios that can be used to interconvert between scale factors optimized for various properties, enabling the derivation of three key scale factors at the effort of optimizing only one of them. A reduced scale factor optimization model is formulated in order to further reduce the cost of optimizing scale factors, and the reduced model is illustrated by using it to obtain 105 additional scale factors. Using root-mean-square errors from the values in the large databases, we find that scaling reduces errors in zero-point energies by a factor of 2.3 and errors in fundamental vibrational frequencies by a factor of 3.0, but it reduces errors in harmonic vibrational frequencies by only a factor of 1.3. It is shown that, upon scaling, the balanced multicoefficient correlation method based on coupled cluster theory with single and double excitations (BMC-CCSD) can lead to very accurate predictions of vibrational frequencies. With a polarized, minimally augmented basis set, the density functionals with zero-point energy scale factors closest to unity are MPWLYP1M (1.009), τHCTHhyb (0.989), BB95 (1.012), BLYP (1.013), BP86 (1.014), B3LYP (0.986), MPW3LYP (0.986), and VSXC (0.986).
Near-infrared Fourier transform Raman and Fourier transform infrared spectra of nodakenetin angelate (C19H20O5), extracted from seeds of Heracleum candolleaum, were recorded and analysed. The root extract of this plant is used as an antiarthritic and nerve tonic. Ab initio SCF Hartree–Fock computations were performed employing the 6–31G basis set for geometry optimization for the prediction of IR and Raman spectral activities and wavenumber calculations. Parameters initially optimized using AM1 calculations were used as the input for ab initio computations. The computed results were used for the interpretation of the vibrational spectra. Important thermodynamic parameters were also provided. The strong band at 1712 cm−1 and medium-intensity band at 1731 cm−1 resulting from ester and lactone carbonyl vibrations, respectively, are identified in the Raman spectrum. The CO stretching band in IR is broadened around 1717 cm−1 owing to the overlapping of ester and lactone carbonyl vibrations. The lowering of the carbonyl stretching vibrations is due to conjugation. The computed values indicate a larger degree of conjugation for the ester group. The characteristic vibrations of the furanocoumarin ring which is part of the molecule were identified. The CH stretching and bending vibrations of the CH3 group of the ester part indicate the presence of hyperconjugation. Vibrational analysis indicates the presence of blue-shifting H-bonds resulting from interaction of the methyl group The large enhancement of in-plane ring stretching and ring breathing modes in the surface-enhanced Raman scattering spectrum indicates that the molecule is adsorbed on the silver surface in a ‘vertical’ configuration, with the lactone ring perpendicular to the silver surface and probably on the opposite side of the lactonic CO group. Copyright © 2004 John Wiley & Sons, Ltd.
Dynamic profiles of various reactivity parameters like hardness, chemical potential, polarizability, phase volume, and electrophilicity index are studied in gaining insights into the ground- (n = 1) and excited- (n = 15) states dynamics of hydrogen and helium atoms. Pertinent time-dependent Schrödinger equations are solved for the ground and excited states of hydrogen atom and the Rydberg state of the helium atom while a generalized nonlinear Schrödinger equation is solved for the ground state of the helium atom, all interacting with external electric fields of different frequencies and intensities. For both the atoms ground states are more stable than the corresponding excited states. Hardness and phase volume can be used as diagnostics for the chaotic ionization from the Rydberg states of those atoms. Other quantities like higher-order harmonics also lend additional support. Dynamic variants of the maximum hardness and minimum polarizability principles are found to be operative. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2003
The IR (3200–30 cm−1) spectra have been recorded for S-methyl-N,N-dimefhylthiocarbamate, (CH3)2NC(O)SCH3, and its isotopomers, S-d3, N-d6 and N-d9, for the gas and liquid. Additionally, the Raman spectra (3200–10 cm−1) for the solid and liquid, with qualitative depolarization ratios, have been obtained for all the isotopes. These data are interpreted on the basis that the s-cis conformer (the S-methyl group oriented eis to the carbonyl group) with Cs symmetry is the only form existing in all three phases for this molecule. A complete vibrational assignment proposed for the -d0 molecule is facilitated by the availability of spectral data for five different isotopomers. A normal coordinate analysis has been carried out utilizing ab initio calculations with the 3–21G* basis set. The potential energy distributions and ab initio calculated frequencies have allowed a clarification of some of the corresponding results obtained from experiment. Structural optimizations and potential surface scan have also been carried out by ab initio calculations with the 3–21G* basis set. These results are compared with some previous studies on this molecule as well as on similar molecules.
A new hybrid exchange–correlation functional named CAM-B3LYP is proposed. It combines the hybrid qualities of B3LYP and the long-range correction presented by Tawada et al. [J. Chem. Phys., in press]. We demonstrate that CAM-B3LYP yields atomization energies of similar quality to those from B3LYP, while also performing well for charge transfer excitations in a dipeptide model, which B3LYP underestimates enormously. The CAM-B3LYP functional comprises of 0.19 Hartree–Fock (HF) plus 0.81 Becke 1988 (B88) exchange interaction at short-range, and 0.65 HF plus 0.35 B88 at long-range. The intermediate region is smoothly described through the standard error function with parameter 0.33.
Arsenic contamination is a leading environmental problem. As such, levels of this toxic metalloid must be constantly monitored by reliable and low-cost methodologies. Because the currently accepted upper limit for arsenic in water is 10 ppb, very sensitive and selective detection strategies must be developed. Herein we describe the synthesis and characterization of a fluorescent chemical probe, namely, ArsenoFluor1, which is the first example of a chemosensor for As(3+) detection in organic solvents at 298 K. AF1 exhibits a 25-fold fluorescence increase in the presence of As(3+) at λ(em) = 496 nm in THF, which is selective for As(3+) over other biologically relevant ions (such as Na(+), Mg(2+), Fe(2+), and Zn(2+)) and displays a sub-ppb detection limit.
Some exact conditions for the extremals of the electrophilicity index, omega = mu(2)/2eta (Parr, R. G.; von Szentpaly, L.; Liu, S. J. Am. Chem. Soc. 1999, 121, 1922), along an arbitrary reaction coordinate, have been carefully examined. Implications within the widely used finite difference approximation for the density-functional based reactivity descriptors, their relationship with the maximum hardness principle, and the reliability of the general relationships have been tested in the framework of computational evidence for some simple systems of chemical interest.
For neutral and charged species, atomic and molecular, a property called absolute hardness η is defined. Let E(N) be a ground-state electronic energy as a function of the number of electrons N. As is well-known, the derivative of E(N) with respect to N, keeping nuclear charges Z fixed, is the chemical potential μ or the negative of the absolute electronegativity χ: μ = (∂E/∂N)Z = -χ. The corresponding second derivative is hardness: 2η = (∂μ/∂N)Z = -(∂χ/∂N)Z = (∂2E/∂N2)Z. Operational definitions of χ and η are provided by the finite difference formulas (the first due to Mulliken) χ = 1/2(I + A), η = 1/2(I - A), where I and A are the ionization potential and electron affinity of the species in question. Softness is the opposite of hardness: a low value of η means high softness. The principle of hard and soft acids and bases is derived theoretically by making use of the hypothesis that extra stability attends bonding of A to B when the ionization potentials of A and B in the molecule (after charge transfer) are the same. For bases B, hardness is identified as the hardness of the species B+. Tables of absolute hardness are given for a number of free atoms, Lewis acids, and Lewis bases, and the values are found to agree well with chemical facts.
Prompted by a recent paper by Maynard and co-workers (Maynard, A. T.; Huang, M.; Rice, W. G.; Covel, D. G. Proc. Natl. Acad. Sci. U.S.A. 1998. 95, 11578), we propose that a specific property of a chemical species. the square of its electronegativity divided by its chemical hardness, be taken as defining its electrophilicity index. We tabulate this quantity for a number of atomic and molecular species, for two different models of the energy-electron number relationships, and we show that it measures the second-order energy change of an electrophile as it is saturated with electrons.