Estimation of high and low UV intensity profiles of mesogenic oxovanadium (IV) salen complexes: Doubling effect of homologue number

This article estimates the high and low UV intensity profiles of mesomorphic oxovanadium (IV) salen [VO (4-C_nH_2n+1O)₂ salen; nVLC] complexes. Structure of these complexes have been optimized using the Density functional B3LYP with 6–31 + G (d) basis set using crystallographic geometry as input. The UV absorption spectral characteristics have been estimated in the UV region by employing the DFT method. The oscillator strength (f) and vertical transition energy (E_V) have been reported corresponding to absorption wavelength (λ_max). Further, some electrochemical properties have been reported for the molecule. The doubling effect of homologue number on the reported parameters has been discussed.     

Substituent and solvent effects on UV‐visible absorption spectra of liquid crystalline disubstituted biphenylcyclohexane derivatives – a computational approach

A computational approach has been carried out on liquid crystalline disubstituted biphenylcyclohexanes (BCHs) of general formula R‐C₆H₁₀‐C₆H₄‐C₆H₄‐X with R: C₃H₇; X: H (BCH30) and R: C₅H₁₁; X: CN (BCH5CN) using the CNDO/S + CI and INDO/S + CI methods. These methods have been employed to calculate and analyze the spectral shifts, and absorbance measurements in UV‐visible range of the systems. The electronic transitions, absorption wavelength, HOMO (Highest Occupied Molecular Orbital), and LUMO (Lowest Unoccupied Molecular Orbital) energies have been calculated. Further, ultraviolet (UV) stability of the molecules has been discussed in the light of absorption wavelength and electronic transition oscillator strength (f). The effect of different solvent media and substituents on transition energies, oscillator strength, and other absorption parameters has also been reported. The present article provides valuable information regarding enhancing the UV stability of molecules by marinating their conductivity. Further, these absorption spectra will provide valuable data base for future computational studies, and the other experimental investigations. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

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

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 (E_HOMO), LUMO (E_LUMO) energies, energy gap (E_g), 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.     

Molecular structure,vibrational spectroscopic and chemical reactivity of nematogenic p-n-alkylbenzoic acids: A comparative computational analysis

Molecular structure and vibrational spectroscopic studies of higher homologous series nematogenic p-n-alkylbenzoic acids (nBAC) that have 6 (6BAC) and 7 (7BAC) 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 levels. A comparision of chemical reactivity such as HOMO (E_H), LUMO (E_L) energies, energy gap (E_g), ionization energy (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 the decrement has occurred in the energy band gap value of isolated molecule with increment in alkyl chain length. This provides valuable information regarding enhancing the stability of liquid crystal materials by maintaining the conductivity.     

Structural,electrochemical and optical properties of 4′-n-alkyl-4-cyanobiphenyl (nCB) – A computational approach

The structures of nCB (n = 6 & 7 where n is the number of carbon atoms in the alkyl chain) have been optimized using the Becke3-Lee-Yang-Parr (B3LYP) hybrid functional with 6–31G+(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 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 photo sensitivity of liquid crystalline alkyl cyanobiphenyl has been presented on ultraviolet (UV) absorption based approach through Density functional theory (DFT) calculations. The structural and electrochemical properties such as HOMO (H), LUMO (L), and energy gap (Eg = E_L – E_H) have been investigated. A comparison of dimers during the different modes of interactions suggests an absorption maxima at longer wavelength for 7CB, indicating the high photo sensitivity. Further, the 6CB dimers exhibit a lower band gap; hence its conductivity is high in comparison with the 7CB dimers.     

Molecular Properties and Order Parameters of Schiff's Base Compounds

The refractive indices n_o, n_c and the order parameters are measured as a function of temperature for the Schiffs base compound PBBA. From the experimental data the molecular polarisabilities and its anisotropies at different wavelengths are calculated using different internal field models. The merits of each model are discussed. Order parameters (P ₂), (P ₄) and other molecular parameters of PBBA and EBBA are also calculated using X-ray diffraction techniques at different temperatures. Comparison with theoretical values shows the relative merits of different experimental techniques. The (P ₂) and (P ₄) values of other members of the Schiff's base compounds, already reported from our laboratory, have been given herewith to show the disagreement with the simple mean field theory. Possible causes for such disagreement have been discussed.     

Structural,spectroscopic properties and theoretical studies of (E)-1-(4-Bromophenyl)-3-(2,3,4-trimethoxyphenyl)prop-2-en-1-one as a potential anti-oxidant agent

The new chalcone compound namely (E)-1-(4-Bromophenyl)-3-(2,3,4-trimethoxyphenyl)prop-2-en-1-one (C₁₈H₁₇BrO₄) is crystallized in the monoclinic crystal system of P2₁/c space group. The unit cell dimensions are: a = 8.0753 (10) Å, b = 21.873 (3) Å, c = 9.3362 (12) Å, α = 90°, β = 99.369 (2), γ = 90° and Z = 4. The single crystal was grown using slow evaporation solution growth technique. The newly synthesized compound was characterized by using IR, ¹H- and ¹³C-NMR, UV-Vis and single crystal X-ray diffraction analyses. Quantum chemical method of Density Functional Theory (DFT) with B3LYP/6-311++G(d,p) has been employed to study the structural and spectral properties of the compound. The electronic absorption spectrum was calculated using the time dependent functional theory (TDDFT) method. The most stable conformer of the title chalcone is identified from the computational results. Hirshfeld surface analysis with fingerprint plots has been used as a graphical tool for visualization and understanding of intermolecular interactions. Intermolecular C?H····O interaction observed stabilize the crystal structure, forming an infinite one dimensional column. The effect of this intermolecular interaction in the solid state can be seen in the difference between the experimental and the theoretically optimized geometrical parameters. The crystal is transparent in the entire visible region and absorptive in the UV region. Information about the size, shape, charge density distribution and site of chemical reactivity of the molecule has been obtained by mapping electron potential (MEP). The other molecular properties like charge transfer are explain using Mulliken population analysis. The antioxidant test indicated that the 2,3,4-trimethoxy substitution on the bromide chalcone to be one of the favorable modification to enhance its metal chelating activity.     

7-Hexyloxy-3-[4’-(3-methylbutyloxy) phenyl]-4H-1-benzopyran-4-one: Study of Smectic behaviour and UV absorption profile

The intermolecular interaction energies between a pair of 7-Hexyloxy-3-[4’-(3-methylbutyloxy) phenyl]-4H-1-benzopyran-4-one (HMBPB) molecules have been estimated with respect to translational and orientational motions. The complete neglect differential overlap (CNDO/S) method has been employed to calculate the net atomic charge and atomic dipole moment components at each atomic center. The modified Rayleigh-Schrodinger perturbation theory 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 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 (300K), and isotropic-smectic transition temperature (412.6K). Molecular arrangements inside a bulk of materials and smectic behavior of the compound in terms of their relative order have been discussed. Translational and rotational rigidity of the molecule has been analyzed to understand the smectic behaviour. The UV absorption profile has been estimated using CNDO/S, and INDO/S methods.     

Copper(II) and lead(II) complexes of 4,4′-bipyridine-<Emphasis Type="Italic">N,N</Emphasis>′-dioxide

Cu(II) and Pb(II) complexes of 4,4′-bipyridine-N,N′-dioxide have been prepared using a solvent-layering system. [Cu₂Cl₄(bpdo)₃(H₂O)₂] . 2(CH₃)₂SO (1) crystallises in P-1, a=8.731(2), b=8.943(2), c=14.408(3) ?, α=102.85(3), β=97.49(3), γ=109.77(3)°. The Cu(II) complex is a z-shaped discrete molecule with a DMSO molecule hydrogen bonded to the host through coordinated water molecule. Crystallisation of PbCl₂, PbBr₂ and PbI₂ with bpdo afforded isostructural 2D coordination polymers. [PbCl₂(bpdo)]_n is monoclinic, C2/c with a=16.3274(7), b=4.0708(1), c=18.6146(8) ?, β=93.73(1)°; [PbBr₂(bpdo)]_n is monoclinic, C2/c with a=16.403(3), b=4.2412(8), c=18.846(4) ?, β=92.59(3)° and [PbI₂(bpdo)]_n is monoclinic, C2/c with a=16.438(3), b=4.538(1), c=18.973(4) ?, β=91.04(3)°. The adjacent metal centres of these polymers are bridged by coordinated Cl⁻, Br⁻ or I⁻ anions as well as by bpdo ligands. These polymers possess no conventional hydrogen bonds.     

Liquid Crystalline Phases in 4-Acetyl-4′-n-Alkanoyloxy-Azobenzenes

Abstract

The preparation and melting behaviour of the homologous series of 4-acetyl-4′-n-alkanoylox-azobenzenes, CH₃-CO-C₆H₄-N?N-C₆H₄-O-CO-(CH₂) _n -CH₃, (with n ranging from zero to 16) is reported. The melting behaviour has been investigated by means of thermal microscopy and differential scanning calorimetry. The experimental results indicate for almost all the compounds the presence of solid state polymorphism and a type A smectic; for one compound a type B smectic phase is also present. Some homologs present, in addition, a nematic phase.     

Synthesis and properties of palladium(II) complexes with sulfur ligands

Complexes of L-2 thiolhistidine (th) and 2-mercaptoimidazole (miz) with Pd(II) were synthesized, Pd(th)₄(NO₃)₂ and Pd(miz)₄Cl₂, and their structure determined by FTIR, UV/VIS, NMR, mass spectroscopy, and X-ray crystallography. For comparison, a Pd(II) complex with thiourea (tu), Pd(tu)₄Cl₂, was prepared. This compound has been reported in the literature. Spectral evidence indicates a single coordination site between the Pd(II) and S for all complexes. A Pd-S stretch band was identified for all complexes. NMR spectra provided evidence for deshielding effects in the complexes from that of its ligands. Charge transfer bands were identified in the UV/VIS spectra for the new complexes as well. The crystal structure for Pd(miz)₄Cl₂ was determined. Unit cell data was found to be:a=8.102(3)Å,b=8.300(3)Å,c=8.304(3)Å. The crystal system is triclinic and the space group isP ¯1.     

A density functional theory study on multiple exciton generation in lead chalcogenides

Abstract

Quantum confined structure-based solar cell is promising two folds increment of the maximum theoretical photovoltaic conversion efficiency i.e., > 60% in comparison with that of the bulk analogs e.g., silicon-based and dye sensitized solar cell (ca. 32% of maximum theoretical efficiency). The key to the significant increment is the ability of the fluorophore to exhibit multiple exciton generation upon absorption photon with sufficient energy. Small size of lead chalcogenides (PbS, PbSe, PbTe) crystals have been reported and proven experimentally could exhibit this unique property. We have investigated few clusters of narrow bandgap lead chalcogenides nanocrystals i.e., (PbS)n, (PbSe)n and (PbTe)n; which n?=?4 - 80. The cluster models were optimized using quantum chemical calculations to the lowest energy geometry at B3LYP/lanl2dz level of theory. The predicted realistic (PbS)₈₀, (PbSe)₅₀, and (PbTe)₇₄ clusters with the size, and bandgap of 4.58?nm (2.00?eV), 4.03?nm (1.51?eV), and 4.84?nm (1.55?eV) are smaller than that of their exciton Bohr radius i.e., 5.01, 13.1, and 24.8?nm respectively. Therefore, the occurrence of multi exciton generation in the clusters is hypothesized upon absorption of photon with E_photon = 2E_g.     

The Dielectric and Optical Properties of the Homologous Series of Cyano-Alkyl-Biphenyl Liquid Crystals

The electric permittivities, refractive indices and densities of the homologous series of alkyl-cyano-biphenyls (C_nH_2n+1.φ.φ.CN) have been measured as a function of temperature in the nematic phases for n = 5 to 9, and in the smectic phases for n = 8 and 9. The results have been analysed in terms of the Maier and Meier theory to yield values for the molecular dipole moments and polarizabilities. Kerr effect measurements on dilute solutions of 44′-n-pentyl-cyano-biphenyl at different temperatures are reported, and in conjunction with similar dielectric and optical measurements have provided results for the free molecule dipole moment and polarizabilites; values for the higher homologues are predicted using a bond additivity model. Bordewijk's theory is applied to the permittivity measurements, and using appropriate molecular parameters, dipole-dipole correlation factors are calculated.     

Spectroscopic,thermal, and X-ray diffraction studies of tetrakis(thiourea) palladium chloride bis (5,7-dimethyl[1,2,4]triazolo[1,5-a]pyrimidine dihydrate

The crystal and molecular structure of the title compound, ·[Pd(S=C(NH₂)₂)₄]Cl₂·2dmtp·2H₂O. has been determined and refined to a finalR=0.034. The cation is centrosymmetric with the Pd atom existing in a square planar geometry with two disparate Pd–S bond distances of 2.3129(9) and 2.292(1)Å. Interatomic parameters are reported for the first non-coordinated dmtp molecule; these suggest the predominance of a particular canonical form in the solid state. The lattice is stabilized via a series H-bonding contacts involving the thiourea. Cl^– and dmtp species. Crystals of [Pd(S=C(NH₂)₂)₄]Cl₂ · 2dmtp · 2H₂O are monoclinic with space groupP2₁/c, and unit cell dimensionsa=15.129(1),b=8.512(1),c=12.663(1) Å, =104.05(1)°.     

Crystallographic Investigations of 3β‐acetoxy‐5α‐cholestan‐6‐one‐semicarbazone ‐ A Steroid

The crystal structure of 3b‐acetoxy‐5a‐cholestan‐6‐one‐semicarbazone (C₃₀H₅₁O₃N₃) has been determined by X‐ray diffraction methods. It crystallizes in the orthorhombic space group P2₁2₁2₁ with cell parameters a = 11.641(1), b = 16.552(1) c = 31.181(4) Å and Z = 8. The structure has been refined to an R‐value of 0.050 for 4407 observed reflections. Two molecules in the asymmetric unit have been observed. In both the crystallographically independent molecules, all the three six‐membered rings (A, B and C ) of steroid nucleus exist in chair conformation, while the five‐ membered ring D exists in 13β distorted‐envelope in molecule‐I and 13β, 14α half‐chair conformation in molecule‐II. Three intermolecular N‐H … O hydrogen bonds have been observed.     

Influence of doping on OH absorption in LiNbO3 crystals

Undoped, Cr doped and Mg, Cr codoped LiNbO₃ crystals were grown by conventional Czochralski technique. Comparative study was carried out using Fourier transform infrared (FTIR) and UV‐Visible spectroscopy. Infrared optical absorption for OH^– ion has been used to study the effect of dopants on the crystals. The peak position of OH^– shift to 3535 cm^‐1 for Mg, Cr codoped crystals compared to 3484 cm^‐1 for undoped and Cr doped crystals. Prominent absorption bands are found in the visible region centered at 480 nm (20833 cm^‐1) and 653 nm (15313 cm^‐1) in Cr doped crystals. Whereas in Mg, Cr codoped crystals these broad absorption bands are red shifted to 517 nm (19342 cm^‐1) and 678 nm (14749 cm^‐1). UV cutoff in Cr doped crystals shift towards higher wavelength compared to undoped LiNbO₃ crystals. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Crystal and molecular structure of N-(Diethylaminothiocarbonyl)-N′-phenyl-benzamidine

The crystal structure of the title compound has been determined by X-ray diffractometer data collected on a CAD-4 diffractometer. C₁₈H₂₁N₃S crystallizes monoclinic, space group P 2₁/n with a = 8.939(1) Å, b = 18.992(3) Å, c = 10.416(2) Å, β = 97.29(2) Å and Z = 4. Least-squares refinement gave a value of R = 0.107 for 2647 observed reflections. The molecule has a configuration which can be described best by Z, E′ and exists in the tautomeric enamine form. The molecules form infinite chains connected by intermolecular N—H … S interactions, with H … S distances of 2.46 Å.     

X-ray structure and NMR assignment of 4-methoxy-4′-methylthio-3,3′-diquinolinyl sulfidea

The title compound (C₂₀H₁₆N₂OS₂) is monoclinic, witha=7.786(3).,b=13.252(3),c=17.162(4) Å, =99.16(3)° and space groupP2₁/n. Two quinoline moieties are nearly perpendicular to each other (112.9(2)°). Both methoxy and methylthio groups are trans-orientated with the respect to the C(3)–S(1)–C(13) plane. Two pairs of the heteroatoms in ortho-positions are in very close contact. The conformation of the molecule explains an unusual¹H NMR spectrum     

Crystal structure of cyanocalix[4]arene methyl ether

The title compound has been prepared by the addition of bromocalix[4]arene methyl ether to CuCN in N-methylpyrrolidone. The crystals belong to the monoclinic space groupP2₁/n witha=13.591(3),b=24.778(5),c=11.057(3)Å,=93.58(2)°, andD _c=1.09 g cm^–3 forZ=4. Refinement based on 1118 observed reflections led to a finalR value of 0.085. The molecule exhibits the partial cone conformation.