Search results for "Effects"
showing 10 items of 2634 documents
The Triplet Excimer of Naphthalene: A Model System for Triplet−Triplet Interactions and Its Spectral Properties
2011
Basic concepts of triplet excimer formation and triplet−triplet interactions between molecules with conjugated π-systems are investigated by means of ab initio quantum chemical calculations, employing the second-order coupled-cluster method CC2 and the second-order propagator method ADC(2). The naphthalene dimer turns out to be a very fruitful model system for which weak and strong electronic coupling can be identified depending on the mutual arrangement of the monomer moieties. From geometry optimizations in the excited state, we determine binding energies, including solvent effects, and transient absorption spectra. The most stable T1 conformation turns out to be a face-to-face arrangemen…
Theoretical Study on the Structures and Electronic Spectra of TCNE2−
2006
Investigations into the charge-separated states and electron-transfer transitions in tetracyanoethylene (TCNE) compiles have recently generated much interest. In this work we present theoretical calculations showing that the most stable structure of the dianion TCNE 2- has D 2d symmetry in vacuum as well as in the solvents dichloromethane and cicetonitrile. By means of the coupled cluster linear response, we compute the vertical electronic spectrum in both the gas phase and solution. The theoreitcal results, are compared to the experimental data and good agreement is achieved.
Charged particles at fluid interfaces as a probe into structural details of a double layer
2011
Electrostatic interactions between charged, distant colloids in a bulk electrolyte solution do not depend on the inherent structure of ions and a solvent forming a double layer. For charged colloids trapped at an interface between an electrolyte and air this no longer holds; as the electrostatic interactions are mediated via air and the field lines determining the interactions originate at the charged surface, these details come into prominence. Using the Langevin-Poisson-Boltzmann equation we investigate how steric effects and the polarization saturation of a solvent effect the contact potential at the colloid surface and, in consequence, the long range interactions between colloids trappe…
Excited state dipole moments and polarizabilities of centrosymmetric and dimeric molecules. I. Model study of a bichromophoric molecule
1988
Abstract Refractometric, dielectric and electro-optical absorption measurements are reported for 1-dimethylamino-2,6-dicyano-4-methyl-benzene (I) and 1,4-bis(4′-dimethylamino-3′,5′-dicyanophenyl)bicyclo[2.2.2]octane (II). The evaluation leads to dipole moments and polarizabilities of the ground state as well as the first dipole allowed singlet state. The experimental res excellently substantiate the method of electro-optical absorption measurements in solution. It is shown that the excited dimer wavefunctions of the bichromophoric molecule II localize by solvent induced local site perturbations.
Intense laser effects on donor impurity in a cylindrical single and vertically coupled quantum dots under combined effects of hydrostatic pressure an…
2010
WOS: 000280235800010
The conductance of lithium-7 fluoride in dioxane-water mixtures at 25�C
1990
Conductance data for lithium-7 fluoride in dioxane-water mixtures covering the range 78.35>D>36 in dielectric constant are presented. These data and other previous data on lithium-7 chloride and lithium-7 iodide were analyzed by the Fuoss 1980 conductance equation in order to find the limiting conductance Δo, the pairing distance R and the conductometric association constant Kλ. Setting Ka=Kλ/VM (where VM is the molar volume of the solvent), the thermodynamic pairing constant and the corresponding change of the free energy Δg were calculated. Correlation among the values found for R and Δg=Δh−TΔs and the properties characteristic of the ions and solvents are discussed.
A density functional theory study for the Diels–Alder reaction between N-acyl-1-aza-1,3-butadienes and vinylamines. Lewis acid catalyst and solvent e…
2002
Abstract The molecular mechanism for the Diels–Alder reaction of N-acyl-1-aza-1,3-butadiene with dimethylvinylamine has been studied using density functional theory methods. This cycloaddition is the nucleophilic attack of the vinylamine to the conjugate position of the unsaturated acyl imine with concomitant ring-closure. The presence of a Lewis acid catalyst coordinated to the acyl oxygen atom decreases markedly the activation energy associated to the nucleophilic attack. This results from an increasing of the electrophilicity of the 1-aza-1,3-butadiene that shift the mechanism from a highly asynchronous concerted process to a polar stepwise one.
Raman and theoretical study of the solvent effects on the sizable intramolecular charge transfer in the push-pull 5-(dimethylamino)-5'-nitro-2,2'-bit…
2006
In this paper, we analyze the degree of intramolecular charge transfer in a push-pull π-conjugated system, 5-(dimethylamino)-5'-nitro-2,2'-bithiophene, from changes in frequencies and relative intensities of its strongestRaman scatterings in a bunch of solvents with different polarities. Density functional theory (DFT) was used as a support of the experimental study. Solvent effects on the molecular and electronic structures and on the vibrational properties were estimated by performing B3LYP/6-31G** calculations within the framework of the polarized continuum model (PCM) developed by Tomasi. Calculations reveal that the molecule is highly polarized in the ground state and behaves as a very…
Structural and spectroscopic study of the Br2...3-Br-pyridine complex by DFT calculations.
2007
Abstract The structure and the Raman vibrational spectrum of the complex Br 2 ⋯3-Br-pyridine are determined by DFT calculations using different parametrizations. The calculations are performed taking into account the effects of the dichloromethane as solvent by the CPCM method. A value of 39 kJ mol −1 for the formation enthalpy and of 1 kJ mol −1 for the formation free energy at room temperature in presence of the solvent is found. The predicted Raman spectrum is compared with the experimental one and the essential features of the spectrum are well reproduced by the B3LYP parametrization. The intensity changes of the bands when going from the free moieties to the complex are also generally …
Magnetic field-induced alignment of molecular rotor-shaped cyclophanes
2010
Molecular pinwheels consisting of dipolar substituted cyclophanes in solution can function as free microscopic rotors in the presence of a homogeneous static magnetic field B and a circularly polarized electric field E rotating on a plane containing B. Owing to the high magnetic anisotropy of [26](1,2,3,4,5,6)cyclophane and [36](1,2,3,4,5,6)cyclophane biased by strong ring currents, ∼1 in 105 molecules are expected to align with the C6 symmetry axis perpendicular to a magnetic field of 21 T. The magnetic-field-controlled alignment of rotor-shaped cyclophanes is insignificantly affected by nonpolar solvents, for example, toluene.