Photoinduced phenomena in corona poled polar organic films

Organic materials have received considerable attention because of their large dipole moments and optical nonlinearities. The optically induced switching of material properties is important for studying the optoelectronic effects including second harmonic generation. Organic materials for photonic applications contain chromophore dipole which consist of acceptor and donor groups bridged by a delocalized pi-electron system. Both theoretical and experimental data show a reversible highly dipolar photoinduced intra molecular charge transfer in betaine type molecules accompanied by change of the sign and the value of the dipole moment. The arrangement of polar molecules in films is studied both by atom force microscopy and surface potential measurements. To understand the photo response of these materials, their spectroscopic and electrical properties are studied. The morphology and photoinduced surface potential switching of the self-assembled monolayers and polymer films are investigated.     

Quantum mechanical parametrization of a conformationally dependent hydrophobic index

An extension of our previous work on the development of a conformationally dependent hydrophobic index is presented. The parameter was computed in four alternative ways based on steric parameters, such as the total molecular surface area or the solvent accessible surface, and on quantum mechanically computed electronic properties, such as the molecular dipole moment, Mulliken charge densities, and a lone–pair index. The method was parametrized based on 110 rigid analogs and all properties required were calculated using the semiempirical methods PM 3, AM 1, and MNDO . Examples of the application of this method in calculating hydrophobic indices are presented.     

The direction of the dipole moments of furan,thiophen, and pyrrole: A controversial question

The report that the dipole moment in the five-membered heterocyclic rings, furan, thiophene, and pyrrole has the positive pole on the heteroatom is contradicted with arguments based on reactivity data, theoretical calculations and moment values of substituted derivatives. In actuality, the dipole moment in furan and thiophene is directed from the ring (positive pole) to the heteroatom (negative pole).     

Gas chromatographic behaviour and pharmacological activity of neuroleptica

Biological activity in vitro, quantified as equilibrium inhibition constants to the dopamine receptor, of a series of neuroleptica are correlated with parameters describing polar and apolar interactions of these molecules with the receptor. Gas-chromatographic retention indices on stationary phases of different polarity are compared with parameters that are classically used in such quantitative structure/activity studies. To describe a polar interactions, a series of classical parameters such as several valence molecular indices and log k′ in a reversed-phase h.p.l.c. system are included; retention indices on the apolar stationary phase, OV101, are used as the gas-chromatographic (g.c.) parameter. To take the more specific polar interactions into account, quantum-chemical charge parameters such as the dipole moment and the charge on atoms directly involved in the interaction were calculated. Retention indices on the more polar phase OV17 are taken as the g.c. parameter for polar interactions. It is shown that the retention indices on OV101 can replace classical parameters describing aspecific or apolar interactions. The retention indices of OV17 do not correlate with biological activity and are worse than the charge parameters.     

Solvent dependence of the one-electron reduction of substituted benzo- and naphthoquinones

Potentials for the one-electron reduction of a series of substituted benzo- and naphthoquinones were measured in 10 aprotic solvents by cyclic voltammetry and used to construct Hammett plots. Hammett reaction constants, ρ, were determined in each solvent and used as indicators of the solvent-mediated stabilization of the charged radical-anion product of the reduction reaction. Correlations of Hammett ρ values with solvent parameters suggest that the Lewis acidity of the solvent, in particular the solvent's ability to donate a partially positive proton, is a consistent predictor of the degree of charge stabilization of the quinone radical anion. Other mechanisms of charge stabilization, including solvent–solute charge transfer complexes and dipole–dipole interactions involving the molecular dipole moment (or an induced dipole moment) of the solvent, were found to be inconsistent predictors of the effect of solvent on one-electron quinone reduction in aprotic media.     

Solvent-Induced Symmetry-Breaking Charge Transfer in an Octupolar Triphenylamine Derivative Resolved with Transient Fluorescence Spectroscopy

The excited-state symmetry-breaking charge transfer (SBCT) dynamics in quadrupolar or octupolar molecules without clear infrared markers is usually hard to be tracked directly. In this work, on the basis of the evolution of instantaneous emission dipole moment obtained by femtosecond transient fluorescence spectroscopy, we presented a real-time characterization of the solvent-induced SBCT dynamics in an octupolar triphenylamine derivative. While the emission dipole moment of the octupolar trimer in weakly polar toluene changes little during the excited-state relaxation, it exhibits a fast reduction in a few picoseconds in strongly polar tetrahydrofuran. In comparison with the uorescence dynamics of dipolar monomer, we deduced that the emitting state of the octupolar trimer in strongly polar solvent, which undergoes solvent-induced structural uctuation, changes from exciton-coupled octupolar to excitation localized dipolar symmetry. In weakly polar solvent, the octupolar symmetry of the trimer is largely preserved during the solvation stabilization.     

On the dipole moments and first-order hyperpolarizability of N,N-bis(4-bromobutyl)-4-nitrobenzenamine

The nonlinear optical molecule N,N-bis(4-bromobutyl)-4-nitrobenzenamine was synthesized. The ground state dipole moment was determined by the Debye-Guggenheim method. A solvent mixture of acetonitrile and toluene was used for the solvatochromic determination of the excited state dipole moment. Excited state has a high value for the dipole moment which indicated a higher degree of charge transfer from the donor to the acceptor moiety on excitation by light. The first hyperpolarizability (beta(ijk)) of the molecule was evaluated assuming the two level model of the first hyperpolarizability.     

Influence of heteroelement on dipole and quadrupole moments of a series of three-membered rings containing a second,third, fourth,or fifth-row atom: a theoretical investigation

The influence of heteroelements on the molecular dipole and traceless quadrupole moments of a series of twenty-two three-membered rings (1–22) was theoretically estimated employing levels of theory such as MP2, CCSD, and PBE1PBE in combination with standard Pople’s basis set. To an accurate evaluation of these properties, additional calculations on the optimized geometries were performed using the correlation-consistent cc-pVDZ and aug-cc-pVDZ basis sets on the three mentioned methods. In particular, the dipole and quadrupole moments from MP2 and CCSD approaches are comparable to each other for the studied molecules, while PBE1PBE calculations were significantly deviated compared to MP2 and CCSD levels. High level of theory and large basis sets seemed to be needed to obtain reliable electrical properties in the heterocycles containing heavy atoms. Results demonstrated that the dipole and quadrupole moments are strongly determined by the nature of the heteroatom into ring skeleton, and its magnitude depends on the polarity of C-heteroelement bond. Dipole moment of these molecules 1–22 showed a clear increase with the increase of electronegativity and the atomic size of heteroatom into ring skeleton. Then, high relative dipole moment was found for three-membered rings containing II, IIIA, VIA, and VIIA elements, which is associated to the high polarization of the C-heteroatom bond. A similar behavior was observed for the quadrupole moments of these three-membered rings.

     

Density functional and molecular orbital study of physical process of inversion of nitrogen trifluoride (NF3) molecule

The physical process of the umbrella inversion of the nitrogen trifluoride molecule has been studied invoking the formalisms of the density functional theory, the frontier orbital theory, and the molecular orbital theory. An intuitive structure and dynamics of evolution of the transition state for the event of inversion is suggested. The physical process of dynamic evolution of the molecular conformations between the equilibrium (C_3v) shape and the planar (D_3h) transition state has been followed by a number of molecular orbital and density functional parameters like the total energy, the eigenvalues of the frontier orbitals, the highest occupied molecular orbital and lowest unoccupied molecular orbital, the (HOMO–LUMO) gap, the global hardness and softness, and the chemical potential. The molecular conformations are generated by deforming the ∠FNF angle through steps of 2° from its equilibrium value, and the cycle is continued till the planar transition state is reached, and the geometry of each conformation is optimized with respect to the length of the N? F bond. The geometry optimization demonstrates that the structural evolution entails an associated slow decrease in the length of the N? F bond. The dipole moment at the equilibrium form is small and that at the transition state is zero and shows a strange behavior with the evolution of conformations. As the molecular structure begins to distort from its equilibrium shape by opening of the ∠FNF angle, the dipole moment starts increasing very sharply, and the trend continues very near to the transition state but abruptly vanishes at the transition state. A rationale of the strange variation of dipole moment as a function of evolution of conformations could be obtained in terms of quantum mechanical hybridization of the lone pair on the N atom. The pattern of charge density reorganization as a function of geometry evolution is a continuous depletion of charge from the F center and piling up of charge on the N center. The continuous shortening of bond length and the pattern of variation of net charge densities on atomic sites with evolution of molecular conformations predicts that the bond moment would decrease continuously. The quantum mechanical hybridization of the lone pair of the central N atom shows that the percentage of s character of the lone‐pair hybrid on the N atom decreases at a very accelerated rate, and the lone pair at the transition state is accommodated in a pure p orbital. The result of the continued destruction of asymmetry of charge distribution in the lone pair on the central N atom due to the elimination of contribution of the s orbital with evolution of molecular conformations is the sharp decrease in lone‐pair moment. The decrease in bond moment is overcompensated by the sharp fall of its offsetting component, the lone‐pair moment, resulting in a net gain in dipole moment with the evolution of molecular geometry. Since the offsetting component decreases very sharply, the net effect is a sharp rise of dipole moment with the evolution of molecular conformations just before the transition state. The lone‐pair moment is zero by virtue of the symmetry of the pure p orbital, the lone pair of the central atom in the transition state, and the sum of the bond moments is zero by symmetry of the geometry. The barrier height is quite high at ～65.45 kcal/mol, which is close to values computed through more sophisticated methods. It is argued that an earlier suggestion regarding the development of high barrier value of NF₃ system seems to be misleading and confronting with the conclusions of the density functional theory. An analysis and a comparative study of the physical components of the one‐ and two‐center energy terms reveals that the pattern of the charge density reorganization has the principal role in deciding the origin and the magnitude of barrier of inversion of the molecule and the barrier originates not from a particular energetic effect localized in a particular region of the molecule, rather the barrier originates from a subtle interplay of one‐ and two‐center components of the total energy. The decomposed energy components show that the F?F nonbonded interaction and N? F bonded interaction favor the formation of transition state, while the one‐center energy terms prohibit the formation of the transition state. The barrier principally develops from the one‐center energy components. The profile of the HOMO is isomorphic and that of the LUMO is homomorphic with the potential energy curve for the physical process of the event of umbrella inversion of the molecule. The variation of the HOMO–LUMO gap, ?ε, the global hardness, η, and the softness, S, as a function of the reaction coordinates of angular deformation of NF₃ molecule are quite consistent with the predictions of the molecular orbital and the density functional theories in connection with the deformation of molecular geometry. The profiles of ?ε, η, and S, as a function of reaction coordinates, mimic the potential energy curve of the molecule. The eigenvalues of the frontier orbitals, and the ?ε, η, S parameters are found to be equally effective theoretical parameters, like the total energy, to monitor the physical process of the inversion of pyramidal molecules. The nature of the variation of the global hardness parameter between the equilibrium shape and the transition state form for the inversion is in accordance with the principle of maximum hardness (PMH). © 2002 John Wiley & Sons, Inc. Int J Quantum Chem, 2002     

Relationship between gas chromatographic behaviour and topological, physicochemical, and quantum chemically calculated charge parameters for neuroleptica

Gas chromatographic retention indices for a number of neuroleptic drugs on an apolar phase, OV-101, and a polar phase, OV-17, are correlated with parameters describing various properties of the separated molecules. The gas chromatographic behaviour is related to the same parameters as those used in quantitative structure activity relationships. The molecular connectivity indices and log k' in a reversed-phase HPLC system were chosen as parameters describing the apolar interactions of the molecules with the stationary phase. As properties involved in more specific interactions, and related to the presence of overall or local polarity, the molecular dipole moment and the charge on the N-atom were selected and quantum chemically calculated. It is found that the retention indices on the apolar phase, OV-101, can be successfully correlated with molecular connectivity indices, which are also used in QSAR studies. The retention indices on OV-17 show a high correlation with the charge on the N-atom. Evidence of the importance of this N-atom in pharmacological activity is known.     

挂式-四氢双环戊二烯热裂解产物分布研究

研究了常压下, 温度为450～650 ℃, 停留时间为15.44～4.03 s条件下的JP-10 (挂式-四氢双环戊二烯)热裂解产物分布. 在相对较长的停留时间下, JP-10热裂解转化率对温度很敏感. 热裂解主要产物为甲烷、乙烯、丙烯、丁烯、丁二烯、环戊二烯、苯、甲苯、苯乙烯、环戊烯的乙烯基取代物及C5, C6异构体(戊二烯、环戊烯的甲基取代物、环己烯、己二烯和环戊二烯甲基取代物), 其中, C1～C4、环戊二烯、苯、甲苯、乙烯基取代环戊烯为初始产物.     

Studies of Solvent Effects on Structure and Low Frequency Vibrational Spectra of 2,4-Dinitrotoluene

Solvent effects on 2,4-dinitrotoluene(2,4-DNT) molecule in different solvents(toluene,ethanol,and water) were studied via DFT PCM method at B3LYP/6-311+G(d,p) level. The influences of these solvents on the molecular structure,vibrational spectra,charge distribution,and dipole moment were studied as well. The results show that PCM computations are successful in describing the vibrational spectra of 2,4-DNT molecules in these solutions and the solvent effects on the low frequency vibrational spectra are weak.     

Atom based parametrization for a conformationally dependent hydrophobic index

An atomic parametrization for the determination of a hydrophobicity index that depends on the molecular conformation is presented. The hydrophobicity parameter was calculated in four alternative ways based on charge densities and atomic contributions to the total molecular surface area and depending on the approach, the molecular dipole moment. The geometries required for the computations were calculated using quantum mechanical semiempirical methods as well as molecular mechanics. The charges were computed using semiempirical methods as well as the Gasteiger method.     

靛玉红及其异构体构效关系的密度泛函理论研究

采用密度泛函理论(DFT)方法计算了靛玉红及其异构体分子的几何构型、电子结构以及前线分子轨道等,研究了结构与抗癌活性之间的关系,探讨了其构效关系上的差异.结果表明,分子是否具有平面构型和广泛共轭体系、3′位C原子的净电荷、分子偶极矩等参数的差异是影响各异构体药效的主要因素.提高3′位C原子的负电荷和增大分子偶极矩将有助于提高化合物的抗癌活性.     

Charge transfer associated with the physical process of hardness equalization and the chemical event of the molecule formation and the dipole moments

In this article, we have basically launched a search whether the dipole charge and dipole moment of heteronuclear diatomics can be justifiably evaluated in terms of charge transfer kernel using the hardness equalization principle as basis. We have derived a formula for computing dipole charge (q) on the basis of hardness equalization principle as q = aδ + b, where “a” and “b” are the constants and “δ” is the kernel of charge transfer from less hard atom to more hard atom during the rearrangement of charge on molecule formation. We have computed the dipole charges and dipole moments of as many as six different sets of compounds of widely diverse physicochemical behavior in terms of the algorithm derived in the present work. The computed dipole charge nicely reveals the known chemicophysical behavior of such compounds as are brought under the study. A comparative study of the nature of variation of theoretically evaluated and experimentally determined dipole moments reveals that there is an excellent agreement between the two sets of dipole data. Thus, the new algorithm derived for the calculation of the dipole charge using the hardness equalization principle as a basis is efficacious in computing the distribution and rearrangement of charge associated with the chemical event of molecule formation. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

Donor—acceptor interactions of substituted benzenes with molecular chlorine and carbon disulfide

CNDO molecular orbital calculations have been performed to analyze donor—acceptor interactions between molecular chlorine and benzene, toluene, mesitylene and hexamethylbenzene and the, as yet, unreported chlorine—hexafluorobenzene and carbon disulfide—benzene pairs. The stabilization energy and the dipole moment and its derivative (?p/?R_CICI) calculated for the benzene—chlorine complex are in good agreement with the estimated experimental values. The trends in the experimental stabilization energies and the Cl-Cl vibrational frequencies with increasing methyl substitution appear to be well reproduced by the calculations. The charge transferred from the benzene donor is polarized toward the outer chlorine atom or sulfur atom. For hexafluorobenzene-chlorine the direction of electronic charge polarization is reversed from that of the benzene and methylbenzene complexes. The calculated results are discussed within the framework of Muliiken's simplified resonance theory for complexes.     

An interpretation of the enhancement of the water dipole moment due to the presence of other water molecules

The dipole moment of the gas phase water monomer is 1.85 D. When solvated in bulk water, the dipole moment of an individual water molecule is observed to be enhanced to the much larger value of 2.9 +/- 0.6 D. To understand the origin of this dipole moment enhancement, the effective fragment potential (EFP) method is used to solvate an ab initio water molecule to predict the dipole moments for various cluster sizes. The dipole moment as a function of cluster size, nH 2O, is investigated [for n = 6-20 (even n), 26, 32, 41, and 50]. Localized charge distributions are used in conjunction with localized molecular orbitals to interpret the dipole moment enhancement. These calculations suggest that the enhancement of the dipole moment originates from the decrease of the angle between the dipole vectors of the lone pairs on oxygen as the number of hydrogen bonds to that oxygen increases. Thus, the decreased angle, and the consequent increase in water dipole moment, is most likely to occur in environments with a larger number of hydrogen bonds, such as the center of a cluster of water molecules.