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Ojha D.P.,Liquid Crystal Research Laboratory
Molecular Crystals and Liquid Crystals | Year: 2012

A comparative computational analysis on two nematogens, p-n-heptylbenzoic acid (7BAC), and p-n-heptyloxybenzoic acid (7OBAC) has been carried out with respect to the translational and orientational motions. 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 with the multicentered-multipole expansion method has been employed to evaluate the long-range interactions, and a 6-exp. potential function has been assumed for the short-range interactions. The minimum energy configurations obtained during the different modes of interactions have been taken as input to calculate the configurational probability using the Maxwell-Boltzmann formula in nonpolar organic solvents, i.e., carbon tetrachloride (CCl4) and chloroform (CHCl3) at room temperature (300K). The most stable configuration of pairing, during the stacking interactions, has been obtained for 7BAC in CCl4. Furthermore, an attempt has been made to analyze the role of oxygen and effect of solvents on nematogens at molecular level. Copyright © Taylor & Francis Group, LLC. Source


Praveen P.L.,Liquid Crystal Research Laboratory | Ojha D.P.,Liquid Crystal Research Laboratory
Molecular Crystals and Liquid Crystals | Year: 2013

In the present paper, molecular structure and ordering in a fluorinated smectogenic compound 4-propyloxyphenyl 4-(4-trifluoromethyl-benzoyloxy) benzoate (FLUORO) with respect to translatory and orientational motions have been reported. The evaluation of net atomic charges and dipole moments at each atomic center has been carried out through the complete neglect differential overlap (CNDO/2) method. The modified Rayleigh-Schrodinger perturbation method along with multicentered-multipole expansion method has been employed to evaluate the long-range intermolecular interactions, while a "6-exp" potential function has been assumed for the short-range interactions. The total interaction energy values obtained through these computations have been used to calculate the probability of each configuration at room temperature (300 K), smectic-isotropic transition temperature (488 K), and above transition temperature (550 K) using the Maxwell-Boltzmann formula. Further, thermodynamic parameters such as Helmholtz free energy and entropy have been computed during the different modes of interactions. An attempt has been made to understand the phase behavior and ordering of the compound based on the thermodynamic parameters introduced in the paper. © 2013 Copyright Taylor and Francis Group, LLC. Source


Ojha D.P.,Liquid Crystal Research Laboratory
Molecular Crystals and Liquid Crystals | Year: 2013

The role of organic solvents on nematogenic p-n-alkoxy cinamic acids (nOCAC) with alkyl chain carbon atoms (n = 6, 8) has been reported with respect to the translational and orientational motions. 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 with the multicentered-multipole expansion method has been employed to evaluate the long-range interactions, and a "6-exp." Potential function has been assumed for the short-range interactions. The minimum energy configurations obtained during the different modes of interactions have been taken as input to calculate the configurational probability using the Maxwell-Boltzmann formula in nonpolar organic solvents, that is, carbon tetrachloride, and chloroform at room temperature (300 K). It has been observed that the molecules show the remarkable behavior in the solvents. A comparison of stacked dimers between both the molecules suggests that the extension of the chain length to eight carbon atoms, a recognizable segregation of dimers into a highly tilted layer structured has been obtained. © 2013 Copyright Taylor and Francis Group, LLC. Source


Praveen P.L.,Liquid Crystal Research Laboratory | Ojha D.P.,Liquid Crystal Research Laboratory
Materials Chemistry and Physics | Year: 2011

The intermolecular interaction energies between a pair of Ethyl para-azoxy benzoate (4EAB) molecules have been computed with respect to translational and orientational motions. The complete neglect differential overlap (CNDO/2) method has been employed to compute the net atomic charge and atomic dipole moment components at each atomic centre. The modified Rayleigh-Schrodinger perturbation theory along with multicentred-multipole 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 total interaction energy values obtained through these computations have been used to calculate the probability of each configuration at room temperature (300 K), smectic-isotropic transition temperature (393 K), and above transition temperature (450 K) using the Maxwell-Boltzmann formula. All possible geometrical arrangements between the molecular pairs have been considered during the different modes of interactions. An attempt has been made to understand the molecular property that influences the macroscopic behaviour and controls the equilibrium between different phases of the chosen compound. Molecular arrangements inside a bulk of materials and smectic behaviour of the compound in terms of their relative order have been discussed. Further, a theoretical model has been developed to explicate the role of molecular rigidity on flexibility of various configurations and phase organization of a smectic liquid crystal. © 2010 Elsevier B.V. All rights reserved. Source


Praveen P.L.,Liquid Crystal Research Laboratory | Ojha D.P.,Liquid Crystal Research Laboratory
Molecular Crystals and Liquid Crystals | Year: 2011

The electronic transitions in the ultraviolet (UV)/visible (VIS) range of nematogenic 4'-n-alkyl-4-cyanobiphenyl (nCB) with butyl (4CB) and hexyl (6CB) groups have been studied. The UV/VIS and circular dichroism (CD) spectra of nCB (n = 4, 6) molecules have been simulated using the TDDFT/B3LYP/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 (HOMO) and lowest unoccupied molecular orbital (LUMO) energies corresponding to the electronic transitions in the UV/VIS range have been reported. Excited states have been calculated via CI-singles (CIS) with semiempirical Hamiltonian ZINDO. Furthermore, two types of calculations have been performed for model systems containing single and double molecules of nCB. The dimer complexes during the different modes of molecular interactions have also been taken into consideration in order to investigate the most energetically stable configuration. These computations provide valuable information regarding the role and flexibility of end chains in a particular phase behavior and UV stability. Copyright © Taylor &Francis Group, LLC. Source

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