Altaf Hussain Pandith

Electron Transport and Nonlinear Optical Properties of Substituted Aryldimesityl Boranes: A DFT Study

A comprehensive theoretical study was carried out on a series of aryldimesityl borane (DMB) derivatives using Density Functional theory. Optimized geometries and electronic parameters like electron affinity, reorganization energy, frontiers molecular contours, polarizability and hyperpolarizability have been calculated by employing B3PW91/6-311++G (d, p) level of theory. Our results show that the Hammett function and geometrical parameters correlates well with the reorganization energies and hyperpolarizability for the series of DMB derivatives studied in this work. The orbital energy study reveals that the electron releasing substituents increase the LUMO energies and electron withdrawing substituents decrease the LUMO energies, reflecting the electron transport character of aryldimesityl borane derivatives. From frontier molecular orbitals diagram it is evident that mesityl rings act as the donor, while the phenylene and Boron atom appear as acceptors in these systems. The calculated hyperpolarizability of secondary amine derivative of DMB is 40 times higher than DMB (1). The electronic excitation contributions to the hyperpolarizability studied by using TDDFT calculation shows that hyperpolarizability correlates well with dipole moment in ground and excited state and excitation energy in terms of the two-level model. Thus the results of these calculations can be helpful in designing the DMB derivatives for efficient electron transport and nonlinear optical material by appropriate substitution with electron releasing or withdrawing substituents on phenyl ring of DMB system.

Optoelectronic and nonlinear optical properties of triarylamine helicenes: a DFT study

AbstractThis work involved the design of a new series of triarylaminehelicenes (TAH) with significant hole transport capacity and enhanced nonlinear optical response. The geometries, electronic properties and nonlinear response of TAH derivatives were studied using density functional theory at the B3PW91/6-311++G (2d, 2p) level. Charge transfer and nonlinear optical response were analyzed and correlated with modifications in geometry and energy levels. Calculations indicated that trivial changes in the torsional angle occur in TAH derivatives with electron-donating substituents as compared to those with electron-withdrawing substituents, resulting in lower reorganization energies for TAH derivatives 2–6. TAH derivatives with an –N(CH3)2 group have the greatest highest occupied molecular orbital (HOMO) level, and thus the least ionization potential, indicating significant hole transfer efficiency as compared to unsubstituted TAH. A decrease in the HOMO–LUMO gap occurs upon substitution with electron-releasing groups, whereas there is an increase in the case of –NO2, –COOH, and –CN TAH derivatives. Topological analysis of the HOMOs of the neutral molecules revealed that these orbitals are concentrated mainly in the helicene backbone, with an important contribution from fused phenyl rings, nitrogen atoms and carbonyl groups. However, the lowest unoccupied molecular orbitals (LUMO) are invariably constituted by fused phenyl rings without any contribution from the central nitrogen atom. Studying the effect of substitution on the nonlinear optical response of TAH derivatives, the calculated polarizability and hyperpolarizability at B3PW91/6-311++G (2d,2p) level of theory exhibited a prominent improvement as compared to unsubstituted TAH. Both electron-donating groups and electron-withdrawing groups result in a red shift in the electronic absorption bands of the substitution derivatives, in particular those with –N(CH3)2 and –NH2 groups. Graphical abstractSchematic representation of an Organic Light Emitting Device (OLED) having TAH as hole transport layer

Analysis of vibrational spectra (FT-IR and VCD) and nonlinear optical properties of [Ru(L)3]2+ complexes

Density functional theory calculations were performed on [Ru(L)3]2+ (L = 1,10-phenanthroline, 2,2′-bipyridine, 2,2′-bipyrimidine, 2,2′-bipyrazine) complexes by employing B3PW91 functional and LAN2DZ basis set to predict their spectra and nonlinear optical response. The geometrical and coordination energy studies explained that the stability of [Ru(L)3]2+ metal complexes depends on the extent of interaction of the dπ orbitals of Ru2+ with the π* ligand orbitals, which is maximum for 1,10-phenanthroline. The two enantiomers of the [Ru(L)3]2+ show IR absorption peaks in the region of 1100–1800 cm−1, and a slight shift occurs to lower frequency by solvent. The vibrational circular dichroism peaks of [Ru(phen)3]2+ had major contribution from out-of-phase stretching of 1,10-phenanthroline rings and a minor contribution from H–C=C–H wagging and C=C stretching of rings. Maximum hyperpolarizability was observed for [Ru(phen)3]2+ due to stronger anharmonicity in the π-electron system. Among the [Ru(L)3]2+ (L = bpy, bpm, and bpz) complexes, [Ru(bpm)3]2+ shows enhanced hyperpolarizability due to increase in the dipole along the X-direction. In derivative Ru2+ complexes, we found that hyperpolarizability depends on electron-donating capability of the substituent. As per FMOs study, the HOMO is predominantly metal fragment based, the LUMO is primarily ligand based, and the larger value of hyperpolarizability corresponds to the lower ELUMO–EHOMO gap, reflecting that nonlinear optical response is a consequence of additive dipolar responses of charge transfer and hyperpolarizability. Graphical Abstract

Theoretical investigations into spectral and non-linear optical properties of brucine and strychnine using density functional theory

The density functional theoretical (DFT) computations were performed at the B3LYP/6-311G++(d, p) level to calculate the equilibrium geometry, vibrational wave numbers, intensities, and various other molecular properties of brucine and strychnine, which were found in satisfactory agreement with the experimental data. The out-of-phase stretching modes of aromatic rings and carbonyl stretching modes in combination with CH stretching modes at stereogenic centers generate VCD signals, which are remarkably efficient configuration markers for these chiral molecular systems. NBOs analysis reveals that the large values of second order perturbation energy (47.24kcal/mol for brucine and 46.93kcal/mol for strychnine) confirms strong hyperconjugative interaction between the orbital containing the lone pair of electron of nitrogen and the neighboring CO antibonding orbital. The molecular electrostatic potential map of strychnine molecule, with no polar groups other than the lone keto group, shows less polarization, which accounts for its lower susceptibility towards electrophilic attack as compared to brucine.

Preparation and characterization of 5-sulphosalicylic acid doped tetraethoxysilane composite ion-exchange material by sol–gel method

In this manuscript, we report the preparation and characterization of sulphosalicylic doped tetraethoxysilane (SATEOS), composite material by sol-gel method as a new ion exchanger for the removal of Ni(II) from aqueous solution. The fine granular material was prepared by acid catalyzed condensation polymerization through sol-gel mechanism in the presence of cationic surfactant. The material has an ion exchange capacity of 0.64 mequiv./g(dry) for sodium ions, 0.60 mequiv./g(dry) for potassium ions, 1.84 mequiv./g(dry) for magnesium ions, 1.08 mequiv./g(dry) for calcium ions and 1.36 mequiv./g(dry) for strontium ions. Its X-ray diffraction studies suggest that it is crystalline in nature. The material has been characterized by SEM, IR, TGA and DTG so as to identify the various functional groups and ion exchange sites present in this material. Quantum chemical computations at DFT/B3LYP/6-311G (d,p) level on model systems were performed to substantiate the structural conclusions based ion instrumental techniques. Investigations into the elution behaviour, ion exchange reversibility and distribution capacities of this material towards certain environmentally hazardous metal ions are also performed. The material shows good chemical stability towards acidic conditions and exhibits fast elution of exchangeable H(+) ions under neutral conditions. This material shows remarkable selectivity for Ni(II) and on the basis of its Kd value (4×10(2) in 0.01M HClO4) some binary separations of Ni(II) from other metal ions are performed.

Adsorption studies of Malachite green on 5-sulphosalicylic acid doped tetraethoxysilane (SATEOS) composite material

We report batch adsorption studies for the removal of Malachite green from an aqueous solution using 5-sulphosalicylic acid doped tetraethoxysilane (SATEOS) composite material, prepared in our laboratory previously. Various variables studied were the initial dye concentration, adsorbent concentration, pH, contact time and temperature. The maximum percentage of colour was removed at the basic pH of 9. The removal data were fitted to Langmuir and Freundlich adsorption isotherm equations. The values of their corresponding constants were determined from the slope and intercepts of their respective plots. The monolayer adsorption capacity of SATEOS at 323 K was found to be 657.89 mg g−1. The values of various thermodynamic parameters, such as ΔG°, ΔS° and ΔH°, were also determined. A pseudo second-order kinetic model and Lagergren first-order kinetic model were also applied to study the adsorption process. The effective diffusion parameter Di values were estimated at different initial dye concentrations. The mechanism of adsorption was studied using Rechienbergs equation where a linearity test indicates a film diffusion controlled adsorption mechanism. The maximum interaction (IE = 1432.54 kJ mol−1) between SATEOS and the dye molecule, calculated using B3PW91 functional and LanL2MB basis set, was observed when the nitrogen atom of the dye lies at a distance of 1.57 A from the hydrogen of the hydroxyl group present on SATEOS molecule.

Sigma donor and pi acceptor characteristics of certain NN-bidentate ligands: a DFT Study

Metal ion binding affinity of three NN bidentate ligands in terms of simple parameters of the conceptual density functional theory is reported. Role of ligand framework for chelate stabilization for ethylenediamine (en) bipyridyl (bpy), and 1,10 phenanthroline (phen) is quantified on the basis of NCCN dihedral angle ( ) and N–N spatial distance. We find that the sigma (σ) donor character of three NN-bidentate ligands follow the order phen < bpy < en, which is quit opposite to their experimentally observed stability constant data. However, the overall binding affinity order is correlative with the chelate stabilization and pi back acceptance characteristics; thereby explaining the experimental stability order. We also studied the effect of some electron donating and electron withdrawing substituents on the sigma bonding affinity and pi (π) bonding behavior of the various substituted phen derivatives. The overall binding affinity of these derivatives was correlated on the basis of electrophilicity index (ω). σ donor character for the ligands was observed to vary in the order NH2 > Ph > OH > CH3 > H > Br > Cl > COOH > NO2 for the substitution at 2 and 9 positions. The trend was found in synergism with their Ortho, Para directing efficiencies.

Exploring the ion exchange and separation capabilities of thermally stable acrylamide zirconium(IV) sulphosalicylate (AaZrSs) composite material

In this work, a hybrid composite material, acrylamide zirconium(IV) sulphosalicylate (AaZrSs) has been synthesized by intercalating acrylamide into zirconium(IV) sulphosalicylate. The synthetic conditions were varied to optimize the ion exchange properties of the material. The characterization of the material was done using SEM, IR, XRD and TGA so as to identify the various functional groups and ion exchange sites present in the material. The ion exchange capacities of some monovalent and divalent cations were investigated in order to know the working capacity of the composite material. Quantum chemical computations at B3LYP/LanL2DZ level were performed to substantiate the structural conclusions based on instrumental techniques. Investigations into the elution behavior, ion exchange reversibility and distribution capacities of the material towards some heavy metal ions were also performed. The distribution coefficients of certain metal ions were determined in different media and following order is observed; Cd(II) > Pb(II) > Zn(II) > Co(II) > Sn(II). Its selectivity was examined by achieving some important binary separations like Co(II)–Cd(II), Pb(II)–Cd(II), Zn(II)–Cd(II) and Sn(II)–Cd(II). The extent of Cd(II) removal was tested by varying the solution parameters like adsorbent dose, adsorbate concentration, pH of the solution, contact time and temperature. The adsorption process followed second order kinetics and adsorption data was best fitted to Langmuir isotherm with correlation coefficient of 0.994. The values of various thermodynamic parameters like ΔG°, ΔS° and ΔH° were also determined. Hence the composite material can be potentially applied to remove Cd(II) from polluted waters.

Synthesis and Characterization of Zirconium-Resorcinol Phosphate; A New Hybrid Cation Exchanger and Dye Adsorbent for Water Treatment

Synthesis and characterization of a new hybrid ion exchange material Zirconiumresorcinol Phosphate (ZrRP) is reported in this study. Synthetic conditions such as reactant concentrations and mixing volume ratio were varied to optimize the ion exchange properties of this material. The material has Na+ ion exchange capacity equal to 1.7 meq/g (dry). X-ray diffraction spectra suggest that it is amorphous in nature. This ion-exchanger was also characterization by SEM, IR and TGA-DTG. Various studies such as determination of ion exchange capacity, elution behaviour and pH titration has been performed for different metal ions such as K+, Ca2+, Sr2+, Mg2+, Ni2+, Cd2+. This material has potential application for removal of these ions from the aqueous systems. Effect of anionic (SDS) and nonionic (TX-100) surfactants has also been studied on the adsorption behavior of ZrRP. The material has been found to be selective for Mg2+and Cd2+. We also found that the material showed remarkable adsorption behavior towards some dyes like malachite green and methylene blue.