Durga P. Ojha

The Influence of Alkyl Chain Length and Solvents on Configurational Probability of Liquid Crystalline Materials: A Computational Approach

The influence of alkyl chain length and solvents on two liquid crystalline materials, p-n-butylbenzoic acid (4BAC), and p-n-pentylbenzoic acid (5BAC) 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 300 K. It has been observed that the increase of alkyl chain length causes a minimization in the binding energy, and increases the total energy of 5BAC molecule. Further, the molecules produce remarkable property in the solvents.

Photosensitivity, substituent and solvent-induced shifts in UV-visible absorption bands of naphthyl-ester liquid crystals: a comparative theoretical approach

The substituent- and solvent-induced shifts in UV-visible absorption bands of naphthyl-ester nematic liquid crystals, viz., 4-octylphenyl-6-octyloxy-2-naphthoate (NAPHE1) and 6-octyloxy-2-naphthylyl-4-octyloxybenzoate (NAPHE2), have been investigated using the DFT, CNDO/S and INDO/S methods. A correlation has been made between molecular charge distribution and phase stability based on Mulliken, Loewdin, AM1, PM3, MNDO, CNDO/S and INDO/S methods. The observed π→π* and n→π* electronic transitions have been reported. The substituent- and solvent-induced shifts in absorption bands, transition energies and energy gaps have been discussed. The photosensitivity of the molecules has been analysed based on these shifts. It has been observed that the substituent has a dominant role on both absorption maxima and energy band gap, whereas the solvent has a dominant role only on absorption maxima, and no effect has been observed on the energy gap. These shifts may provide beneficial consequences in determining the end use of compounds.

Effect of substituent on UV–visible absorption and photostability of liquid crystals: DFT study

The electronic transitions in the ultraviolet–visible (UV–Vis) range of two nematogens, namely 4′-cyanophenyl-4-n-pentylbenzoate and 4′-cyanophenyl-4-n-pentoxybenzoate, have been studied. The UV–Vis and circular dichroism spectra of these 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 and lowest unoccupied molecular orbital energies corresponding to the electronic transitions in the UV–Vis range have been reported. The excited states have been calculated via configuration interaction singles with semi-empirical Hamiltonian ZINDO (Zerners intermediate neglect of differential overlap method). Further, the effect of substituent on ultraviolet absorption and photostability of the molecules has been discussed. The photostability of the molecules has been investigated in order to understand the application and operation with ultraviolet and visible light regions.

Role of molecular interactions and end chain length on the photosensitivity of liquid crystalline alkyl cyanobiphenyl dimers – UV absorption-based approach through DFT calculations

In this paper, the photosensitivity of liquid crystalline alkyl cyanobiphenyl (nCB: n = 6, 7; n is the number of carbon atoms in the alkyl chain) dimers has been presented through density functional theory (DFT) calculations. The nCB structures have been optimized using the Becke, three-parameter, Lee–Yang–Parr hybrid functional with the 6-31+G (d) basis set using the crystallographic geometry as input. The electronic structures of the dimer molecules have been computed using the optimized geometries. The spectra of the dimer molecules have been calculated by employing the DFT method. The excited states have been calculated via configuration interaction singles with the semi-empirical Hamiltonian Zerner intermediate neglect of differential overlap. The influence of molecular interactions and the end chain length on ultraviolet absorption spectral characteristics and the photosensitivity of the compounds has been discussed. These results offer a hint for the protection of various optical devices from the intense light induced damages, and to model photosensitivity.

The Interesting Property of Strong Polar Group Nematogens in Organic Solvents – A Computational Study

The interesting property of strong polar group nematogens, 4′-n-alkyl-4-cyanobiphenyl (nCB) with pentyl (5CB), and heptyl (7CB), groups that are of commercial and application interest has been studied 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 (CCl4), and chloroform (CHCl3) at room temperature 300 K. It has been observed that the molecules show the remarkable property in the organic solvents. The interaction energies of dimer complexes have been taken into consideration in order to investigate the most energetically stable configuration. An attempt has been made to develop a new and interesting model for nematogens at molecular level.

Effect of Molecular Interactions and Homologue Number on UV Absorption Spectra of Liquid Crystalline Alkyl Cyanobiphenyl Dimers: DFT Calculations

The ultraviolet (UV) absorption spectra of the liquid crystalline dimer complexes of 4′-n-alkyl-4-cyanobiphenyls (nCB: n = 3, 4, 5 where n is the number of carbon atoms in the alkyl chain) have been presented. The nCB structures have been optimized using the density functional Becke3-Lee-Yang-Parr (B3LYP) hybrid functional with 6-31+G (d) basis set using the crystallographic geometry as input. The electronic structures of the dimer molecules have been computed using the optimized geometries. The spectra of the dimer molecules have been calculated by employing the density functional theory (DFT). The features of electronic transitions and excited states have been calculated via configuration interaction singles (CIS) with the semiempirical Hamiltonian Zerner intermediate neglect of differential overlap (ZINDO). The various modes of molecular interactions and the homologue number are found to be structural parameters affecting the formation of mesophases, UV absorption spectral characteristics, and photo stability of the compounds. These results offer a hint for the calculations involving the different modes of molecular interactions, and separations between dimers, to model photo stability or in tuning the absorbing chromophore to match the wavelength of desired application.

Vibrational spectra, electronic properties and effect of alkyl chain length on chemical stability of nematogens – A comparision using DFT and HF methods

ABSTRACT The vibrational spectra of lower homologous series of nematogenic p-n-alkylbenzoic acids (nBAC) with 4 (4BAC) and 5 (5BAC) carbon atoms in the alkyl chain have been investigated using the Density Functional Becke3-Lee-Yang-Parr (B3LYP) level with the basis set 6–31++G(d.p) and Hartree Fock (HF) with the same basis set. The observed vibrational spectra has been resolved and assigned in detail for comparision with both the molecules. These results indicate that DFT and HF values are slightly different at both the level. A comparision of electronic properties such as HOMO (EHOMO), LUMO (ELUMO) energies, energy gap (Eg), ionization potential (I), electron affinity (A), electro negativity (χ), chemical hardness (η), electronic chemical potential (μ), electrophilicity index (ω), and softness (S) has been made. It has been observed that decrement occurred in the energy band gap value of isolated molecule with increment in alkyl chain length. This provides valuable information regarding the stability of liquid crystal materials.

Theoretical study of closo-decaborate novel nematogen: Thermodynamic behavior and phase stability

ABSTRACT The present article deals with the thermodynamic behavior and phase stability of closo-decaborate nematogen viz. dinitrogen-10-(4-pentyl-1-thiacyclohexyl)-closo-decaborate (DPTD) at a molecular level. The atomic net charge and dipole moment at each atomic center have been evaluated using the complete neglect differential overlap (CNDO) 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), nematic–isotropic transition temperature (435 K), and above transition temperature (500 K) using the Maxwell–Boltazman formula. Further, the entropy of each configuration has been computed during the different modes of interactions. The adopted framework provides valuable information on thermodynamic behavior, and phase stability of novel nematogen based on parameters, i.e., molecular and thermodynamic, introduced in this article.

Phase stability and ordering of nematogen at molecular level: A computer-aided modeling

ABSTRACT The present article deals with the phase stability and ordering of nematogen, viz., 6-octyloxy-2-naphthylyl-4-octoxybenzoate (ONOB) at molecular level. A comparative picture has been given between molecular charge distribution, and phase stability based on AM1, PM3, CNDO, and MNDO methods. 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, nematic-isotropic transition temperature, and above transition temperature using the Maxwell–Boltzmann formula. Further, the entropy of each configuration has been computed during the different modes of interactions. An effort has been made to develop a computational model at molecular level based on configurational entropy, and translational rigidity parameters introduced in this article.

Structural and optical properties of novel nematogens based on DFT and semiempirical method—A comparative picture

ABSTRACT A comparative picture of structural, and optical properties of nematogens, viz., bis(4-propyloxyphenyl) 1,12-dicarba-closo-dodecaborane-1,12-dicarboxylate (Nematic1), and bis(4-butoxyphenyl) 1,10-dicarba-closo-decaborane-1,10-dicarboxylate (Nematic2) have been studied in ultraviolet (UV) and visible (Vis) regions. The structure of nematogens have been optimized using the Density functional B3LYP with 6–31+G (d) basis set using crystallographic geometry as input. The electronic structure of the molecules has been evaluated using the DFT, and semiempirical methods, namely; CNDO/S (complete neglect of differential overlap/ spectroscopy) and INDO/S (intermediate neglect of differential overlap/ spectroscopy). The HOMO (Highest Occupied Molecular Orbital)/LUMO (Lowest Unoccupied Molecular Orbital) energies, and oscillator strength (f) have also been reported using these methods. The electronic absorption spectra of the molecules have been simulated by employing the DFT method, semiempirical parameterizations. Molecular charge distribution and phase stability of these nematogens have been analyzed based on Mulliken and Loewdin population analysis. It has been observed that Nematic2 molecule shows the much flexibility for electronic transitions over a long wavelength region that leads to high photosensitivity.