Ordering of a Strong Polar Nematogen (6CBB) in a Dielectric Medium: A Computational Analysis

Praveen, P. Lakshmi; Ojha, Durga P.

doi:10.1080/15421406.2010.504659

Cited by 3 publications

(1 citation statement)

References 16 publications

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“…An appropriate modeling of this fundamental molecular feature relies on the possibility of assigning a partial charge to all atomic centers [20]. To parametrize the molecular interactions for computational studies, atom positioned partial charges are helpful [21].…”

Section: A Molecular Charge Distribution and Phase Stabilitymentioning

confidence: 99%

Computational analysis of molecular properties and spectral characteristics of cyano-containing liquid crystals: Role of alkyl chains

Praveen¹,

Ojha²

2011

Phys. Rev. E

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The electronic transitions in the uv-visible range of 4'-n-alkyl-4-cyanobiphenyl (nCB) with propyl, pentyl, and heptyl groups, which are of commercial and application interests, have been studied. The uv-visible and circular dichroism spectra of nCB (n = 3,5,7) molecules have been simulated using the time dependent density functional theory Becke3-Lee-Yang-Parr hybrid functional-6-31 + G (d) method. Mulliken atomic charges for each molecule have been compared with Loewdin atomic charges to analyze the molecular charge distribution and phase stability. The highest occupied molecular orbital and lowest unoccupied molecular orbital energies corresponding to the electronic transitions in the uv-visible range have been reported. Excited states have been calculated via the configuration interaction single level with a semiempirical Hamiltonian (intermediate neglect of differential overlap method, as parametrized by Zerner and co-workers). Further, two types of calculations have been performed for model systems containing single and double molecules of nCB. Furthermore, the dimer complexes during the different modes of molecular interactions have also been studied. The interaction energies of dimer complexes have been taken into consideration in order to investigate the most energetically stable configuration. These studies are helpful for understanding the role and flexibility of end chains, in particular, phase behavior and stability.

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Section: A Molecular Charge Distribution and Phase Stabilitymentioning

confidence: 99%

Computational analysis of molecular properties and spectral characteristics of cyano-containing liquid crystals: Role of alkyl chains

Praveen¹,

Ojha²

2011

Phys. Rev. E

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Semi-empirical analysis on electronic spectra and ultraviolet stability of nematic liquid crystals: effect of solvent and substituent

Praveen¹,

Ojha²

2011

Liquid Crystals

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To cite this article: P. Lakshmi Praveen & Durga P. Ojha (2011) Semi-empirical analysis on electronic spectra and ultraviolet stability of nematic liquid crystals: effect of solvent and substituent, Liquid Crystals, 38:8, 963-970, A semi-empirical analysis has been carried out on two nematic liquid crystals, 4-cyanophenyl-4 -n-pentylbenzoate (CPPB) and 4-cyanophenyl-4 -n-pentoxybenzoate (CPPOB), using the CNDO/S + CI and INDO/S + CI methods. These methods have been applied to simulate and analyse the electronic structures, spectra and ultraviolet (UV) stability of the systems. Phase stability of the systems has also been studied based on molecular charge distribution. The electronic transitions, absorption wavelength, HOMO and LUMO energies are calculated. Furthermore, UV stability of the molecules is discussed in the light of absorption wavelength and electronic transition oscillator strength (f ). The effect of solvent and substituent on these factors is discussed. A comparison among different solvents is also made. These absorption spectra will provide a valuable database for further computational analysis and the other experimental investigations. IntroductionLiquid crystals represent a class of complex fluids that has opened many doors for us to learn a great deal about molecular interactions [1], phase behaviour, transitions and the art of soft condensed matter. These molecular fluids show specific optical properties due to the anisotropy of molecular organisation [2]. This anisotropy plays an important role in applications of the electrical effect, display devices, spatial modulators, etc. The bulk order in these materials has profound control on the way light [3] and electricity behave in the material. A unique insight into this behaviour provides not only information about the particular material under consideration, but also about the global properties of anisotropic fluids and their relationships to other chemical structures and/or physical phenomena.Despite their various applications [4][5][6][7], liquid crystals (LCs) belonging to the 4-cyanophenyl-4 -n-alkylbenzoate (CPnB) homologous series and their composites are less studied than those from cyanobiphenyl series. The simulation of electronic spectra by computational chemistry tools is particularly appealing since a large number of methods have been elaborated and employed to calculate the molecular vertical excitation energies, absorption wavelength and oscillator strength of electronic transitions.In view of this, methods based on Time Dependent Density Functional Theory (TDDFT)

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Thermodynamic Stability of the Nematic Phase and Configurational Entropy of Mesogens: A Molecular Simulation Approach

Praveen¹,

Ojha²

2011

Molecular Crystals and Liquid Crystals

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The thermodynamic stability of the nematic phase and the configurational entropy of mesogens-p-n-pentylbenzoic acid (5BAC) and p-n-hexylbenzoic acid (6BAC)-have been studied. The atomic net charge and dipole moment components at each atomic center have been evaluated using the complete neglect differential overlap (CNDO/2) method. The modified Rayleigh-Schrodinger perturbation theory along with multicenteredmultipole expansion method has been employed to evaluate the long-range intermolecular interactions, while a "6-exp" potential function has been assumed for short-range interactions. The interaction energy values obtained with respect to translational and orientational motions during the different modes of molecular interactions have been taken as input to estimate the configurational entropy and Helmholtz free energy at room temperature, nematic-isotropic transition temperature, and above transition temperature. The observed difference in free energy of the molecules between the mesophase and the crystal phase during in-plane interactions suggests the thermodynamic stability of the nematic phase. Further, the comparable values of translational entropy during stacking and in-plane interactions are helpful to understand the relative flexibility/stability of one configuration over the other.

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Ordering of a Strong Polar Nematogen (6CBB) in a Dielectric Medium: A Computational Analysis

Cited by 3 publications

References 16 publications

Computational analysis of molecular properties and spectral characteristics of cyano-containing liquid crystals: Role of alkyl chains

Computational analysis of molecular properties and spectral characteristics of cyano-containing liquid crystals: Role of alkyl chains

Semi-empirical analysis on electronic spectra and ultraviolet stability of nematic liquid crystals: effect of solvent and substituent

Thermodynamic Stability of the Nematic Phase and Configurational Entropy of Mesogens: A Molecular Simulation Approach

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