Jyotirmoy Deb

Hockey-stick-shaped mesogens based on 1,3,4-thiadiazole: synthesis, mesomorphism, photophysical and DFT studies

ABSTRACT New hockey-stick-shaped 2,5-diphenyl-1,3,4-thiadiazole-containing mesogens have been designed and synthesised. These molecules possess 4-n-alkoxy chain at the elongated arm whereas and 4-n-butyloxy chain at the shorter arm of the molecule. The compounds are fluorescent and emission located in the violet to blue region with a large stoke shift observed in polar solvents. No substantial solvatochromic effect was found in the absorption maxima, but in the emission, a red shift was observed with increasing the solvent polarity. In the solid thin film, compounds emitted green light. The compounds having longer chain (n > 8) exhibit SmA and SmC phase, while the compounds with shorter chain at one end of the molecule display nematic and SmC phase. The density functional theory study has been carried out to investigate the stable configuration and the influence of solvent on bond length, bond angle, bending angle, dipole moment, polarisability of the molecule. It also enables us to predict the possible reactive sites and effect of solvent on the chemical reactivity descriptors. Our study concludes that the molecule becomes more reactive in solvent compared to gas. The large voltage holding ratio confirms that this molecule may be used for active matrix display applications. Graphical Abstract

First principle study of adsorption of boron-halogenated system on pristine graphyne

To ensure the possibility of using graphyne as a gas sensor, we have studied the adsorption of boron-halogenated system on pristine graphyne with the help of density functional theory using generalized gradient approximation. Depending on binding energy the most stable orientation, adsorption strength and optimal distance between the above mention molecules and graphyne surface have been determined. The band gap of graphyne slightly increases with the adsorption of the boron-halogenated system. The graphyne system behaves as n-type semiconductor when it interacts with BI3 and BCl3 molecules, and it behaves as p-type semiconductor when interaction with BF3 molecule takes place. Our result reveals that the electronic properties of pristine graphyne are highly influenced by the adsorption of boron-halogenated molecule. We have observed that pristine graphyne has zero electric dipole moment, but with the interaction of boron-halogenated molecule, a significant change in the electric dipole moment takes place. Hence, by measuring the electric dipole moment change, graphyne-based gas sensor can be design for the detection of above-mentioned molecules.

A computational study on structure, stability and bonding in Noble Gas bound metal Nitrates, Sulfates and Carbonates (Metal = Cu, Ag, Au)

AbstractA density functional theory based study is performed to investigate the noble gas (Ng = Ar-Rn) binding ability of nitrates, sulfates and carbonates of noble metal (M). Their ability to bind Ng atoms is assessed through bond dissociation energy and thermochemical parameters like dissociation enthalpy and dissociation free energy change corresponding to the dissociation of Ng bound compound producing Ng and the respective salt. The zero-point energy corrected dissociation energy values per Ng atom for the dissociation process producing Ng atom(s) and the corresponding salts range within 6.0–13.1 kcal/mol in NgCuNO3, 3.1–9.8 kcal/mol in NgAgNO3, 6.0–13.2 kcal/mol in NgCuSO4, 3.2–10.1 kcal/mol in NgAgSO4, 5.1–11.7 kcal/mol in Ng2Cu2SO4, 2.5–8.6 kcal/mol in Ng2Ag2SO4, 8.1–19.9 kcal/mol in Ng2Au2SO4, 5.7–12.4 kcal/mol in NgCuCO3, 2.3–8.0 kcal/mol in Ng2Ag2CO3 and 7.3–18.2 kcal/mol in Ng2Au2CO3, with a gradual increase in moving from Ar to Rn. For a given type of system, the stability of Ng bound analogues follows the order as Au > Cu > Ag. All dissociation processes are endothermic in nature whereas they become endergonic as well in most of the cases of Kr-Rn bound analogues at 298 K. Natural population analysis along with the computation of Wiberg bond indices, and electron density analyses provide insights into the nature of the Ng-M bonds. The Ng-M bonds can be represented as partial covalent bonds as supported by the different electron density descriptors. Graphical AbstractDifferent nitrates, sulfates and carbonates of noble metals (M = Cu, Ag, Au) can bind noble gas (Ng) atoms quite effectively. The M-Ng bonds in these compounds are found to be partially covalent in nature.

Theoretical investigation of electronic, vibrational, and nonlinear optical properties of 4-fluoro-4-hydroxybenzophenone

ABSTRACT The present study emphasizes on structural, opto-electronic, vibrational, and nonlinear properties, at the electronic structure level, on the 4-fluoro-4-hydoxybenzophenone molecule using the first principles calculation. Detailed vibrational assignments of the wavenumbers are carried out on the basis of potential energy distribution and a good agreement between the reported and calculated wavenumbers has been observed. Furthermore, the molecular electrostatic potential surface predicts the reactive site of the molecule. From the time dependent density functional theory analysis of UV-visible spectra, a red shift has been observed at the maximum absorption wavelength when the gaseous medium is replaced by a solvent medium. The 4-fluoro-4-hydroxybenzophenone molecule possesses large hyperpolarizability value which implies its usefulness in nonlinear optical applications.

Density functional theory study of pristine and transition metal doped fullerene

Density functional theory (DFT) methodology have been used to investigate the global reactivity parameters and non-linear optical properties of pristine C20 and C19X (X = Fe, Co) fullerenes. We find that noticeable structural change takes place in C20 when one of its carbon atoms is substituted with Fe or Co. The energy gap of the doped fullerenes also decreases significantly making these more reactive as compared to C20. The negligible static first hyperpolarizability and zero dipole moment of C20 climb to a considerably higher value even for the presence of single dopant atom. Considering all the studied properties, it may be inferred that the applicability of C20 fullerene as a nanoelectronic and non-linear optical (NLO) material would increase on doping with Fe and Co atom. Specifically, C19Fe would be better among them.

The Influence of the Substitution of Transition Metals on Pristine C20: A DFT Study

The stabilities and reactivities of two transition metal (X=Cu, Zn)-doped structures of C20 fullerene have been investigated by density functional theory approach. We have observed a noticeable str...

Confinement of water molecule inside (2, 2) graphyne nanotube

Using density functional theory (DFT) calculations with generalized gradient approximation, the interaction between H2O molecule and (2, 2) graphyne nanotube (GNT) has been investigated. The stable configuration due to the insertion of H2O molecule inside (2, 2) GNT is determined on the basis of binding energy. The band gap of the GNT decreases due to the confinement of H2O molecule. The charge analysis reveals that electrons are shifted from the H2O molecule to the GNT. The electronic property of the GNT is highly influenced by the presence of H2O molecule; thus, we may design a GNT based sensor for the detection of water molecule.

A first principle study of phosphorous doped graphyne

Based on density functional theory (DFT) calculation with generalized gradient approximation (GGA), we have investigated the effect of doping by phosphorous (P) atom at ring and chain position on the electronic properties of graphyne. The stability of the P-doped graphyne system has been determined on the basis of cohesive energy. Doping at chain position shows the possibility of modulating its band gap which might be useful for nano-electronics application. The surprising change from semiconducting to metallic behavior when P atom is placed at ring position of graphyne might be utilized in electronics for the fabrication of metal-semiconductor interfaces and also as an electrode in batteries.

Transition metal doped (X = V, Cr) CdS monolayer: A DFT study

In this work based on density functional theory approach with generalized gradient approximation we have investigated the effect doping and co-doping of transition metal atoms in CdS monolayer shee...

Characterizing the sensitivity of bonds to the curvature of carbon nanotubes

The way the bonding and reactivity of armchair carbon nanotubes depends on the curvature of the nanotube has been investigated using density functional theory. To understand the nature of the interaction between atoms in the nanotube, the Wiberg bond index, natural bond order analysis, and topological electron density analysis have been performed. All these tools confirm that the bonds in the hydrogen-capped carbon nanotubes considered here are primarily covalent. As the diameter of the nanotube decreases and its curvature increases, the covalency (bond order) decreases, a conclusion that is supported by the increase of the bond lengths and also the decrease of the electron density and the energy density along the bond paths as the curvature increases. To shed light on the orbital contribution in bond formation and the most effective interaction between donor bonding orbital and acceptor antibonding orbital, analysis of natural bond orbitals is carried out. We have observed that the higher the nanotube diameter is, the higher the energy gap.