Bose-Einstein condensation and Casimir effect of trapped ideal Bose gas in between two slabs

We study the Bose-Einstein condensation for a 3-d system of ideal Bose gas which is harmonically trapped along two perpendicular directions and is confined in between two slabs along the other perpendicular direction. We calculate the Casimir force between the two slabs for this system of trapped Bose gas. At finite temperatures this force for thermalized photons in between two plates has a classical expression which is independent of ħ. At finite temperatures the Casimir force for our system depends on ħ. For the calculation of Casimir force we consider only the Dirichlet boundary condition. We show that below condensation temperature (T_c) the Casimir force for this non-interacting system decreases with temperature (T) and at , it is independent of temperature. We also discuss the Casimir effect on 3-d highly anisotropic harmonically trapped ideal Bose gas.     

Alkali metal ion mediated self-assembly of vanadium(V) ions and pyrazole based polydentate ligands leading to the formation of helix, double helix and supramolecular cage-like structures

The anionic cis-dioxovanadium(V) complex species LVO₂⁻ and L₁VO₂⁻ of two tridentate ONO ligands (H₂L and H₂L₁) can bind alkali metal ions in a bis-monodentate fashion like a bridging carboxylate group. Here H₂L (N′-[(E)-(2-hydroxyphenyl)methylidene]-3-methyl-1H-pyrazole-5-carbohydrazide) and H₂L₁ (N′-[(1E)-1-(2-hydroxyphenyl) ethylidene]-3-methyl-1H-pyrazole-5-carbohydrazide) are Schiff base ligands generated by the condensation of 5-methyl 3-pyrazole carbohydrazide with salicylaldehyde and o-hydroxy acetophenone. The six products thus obtained are water soluble polymeric compounds in which the complementary units are held together by the simultaneous use of hydrogen bonding and coulombic interactions. [L₁VO₂Li(H₂O)₂]_∞ (2), [LVO₂Na(H₂O)₂]_∞ (3) and [LVO₂K(H₂O)₂]_∞ (5) have been crystallographically characterized. Crystallographic characterization reveals that 2 and 3 are polymeric helicates and 5 is a polymeric cluster with L₁VO₂⁻ or LVO₂⁻ units bridging the labile alkali metal ions which occupy positions on the axis of the polymeric chain.     

Synthesis, X-ray crystal structures, spectroscopic and cyclic voltammetric studies of Cu(II) Schiff base complexes of pyridoxal

Two mononuclear Cu(II) complexes, [Cu(L¹H₂)](ClO₄)_1.25Cl_0.75·1.25H₂O (1) and [Cu(L²H₂)](ClO₄)₂ (2), of the pyridoxal Schiff base ligands N,N′-dipyridoxylethylenediimine (L¹H₂) and N,N′-dipyridoxyl-1,3-propanediimine (L²H₂) are reported. X-ray crystal structures of both complexes are also reported. In both complexes the pyridoxal nitrogen atoms remain protonated. In the solid state, the tetradentate Schiff base ligand is virtually planar in 1, while in 2 the ligand conformation is like an inverted umbrella. In cyclic voltammetry experiments it is found that in these complexes the Cu(III) and Cu(I) states are more easily accessible than in their salen type analogs. The pyridoxal Schiff base complexes are also found to be resistant to oxidative electro-polymerization, unlike their corresponding salicyl aldehyde Schiff base complexes.     

A terpyridyl-imidazole (tpy-HImzPh3) based bifunctional receptor for multichannel detection of Fe2+ and F- ions

The X-ray crystal structures of the tridentate ligand, 4'-[4-(4,5-diphenyl-1H-imidazol-2-yl)-phenyl]-[2,2':6',2']terpyridine (tpy-HImzPh(3)) and its bis-homoleptic iron(ii) complex of composition [Fe(tpy-HImzPh(3))(2)](2+) have been determined, showing that the ligand crystallized in a monoclinic form with the space group P2(1)/c while its Fe(II) complex crystallizes in an orthorhombic form with space group Fddd. Both the anion and cation binding properties of the receptor were thoroughly investigated in dimethylformamide-acetonitrile (1?:?9) solution using absorption, emission, and (1)H NMR spectral studies which revealed that the receptor acts as a sensor for both F(-) and Fe(2+). In the presence of excess F(-) ion, deprotonation of the imidazole N-H fragment of the receptor occurs, an event which is signaled by the development of a yellow color visible with the naked eye. The estimated value of the equilibrium constant of the receptor with F(-) is 1.9 × 10(4) M(-1). Deprotonation is also observed in the presence of hydroxide. The receptor also shows colorimetric and fluorimetric sensing ability towards Fe(2+) ions. The binding site for the metal ion in the system has been unambiguously established by single-crystal X-ray diffraction studies of the Fe(II) complex of the receptor. The influence of solvents on the absorption and fluorescence spectra of the receptor has been investigated in detail. Cyclic voltammetric (CV) and square wave voltammetric (SWV) measurements carried out in dimethylformamide-acetonitrile (2?:?3) provided evidence in favor of cation (Fe(2+)) and anion (F(-)) concentration dependent electrochemical responses, enabling the ligand to act as a suitable electrochemical sensor for F(-) and Fe(2+) ions.     

Highly Sensitive ‘on–off’ Pyrene Based AIEgen for Selective Sensing of Copper (II) Ions in Aqueous Media

A Fluorescent chemosensor based on pyrene scaffold, 5-diethylamino-2-(pyren-1-yliminomethyl)-phenol (PDS) is synthesized using condensation method. It displays novel aggregation-induced emission (AIE) phenomena in its aggregated/solid state. The AIE characteristic of PDS is studied in CH₃CN/H₂O mixtures at different volume percentage of water and morphology of the aggregated particles are investigated by DLS and optical fluorescence microscopic study. The probe is aggregated into ordered one-dimensional (1-D) rod like microcrystals and exhibit high efficiency of solid-state emission with green colour. By taking advantage of its interesting AIE feature, the aggregated hydrosol has been utilized as ‘off–on’ type fluorescence switching chemosensor with superb selectivity and sensitivity towards Cu²⁺ions and the limit of detection (LOD) was calculated as low as 6.3 µM. A high Stern–Volmer quenching constant was estimated to be 2.88?×?10⁵ M^?1. The proposed chemosensor with AIE feature reveals a prospective view for the on-site visual recognition of Cu²⁺ ions in fluorescent paper strips and the synthesized probe is also exploited to find out the concentration of Cu²⁺ions in real water samples.

     

Effect of pH on the photophysical and redox properties of a ruthenium(II) mixed chelate derived from imidazole-4,5-dicarboxylic acid and 2,2'-bipyridine: an experimental and theoretical investigation

Combined experimental and DFT-TD-DFT computational studies were utilized to investigate the structural and electronic properties of mixed-ligand monometallic ruthenium(II) complexes of compositions [(bpy)(2)Ru(H(2)Imdc)](+) (1(+)), its N-H deprotonated form [(bpy)(2)Ru(HImdc)] (1), and COOH deprotonated form [(bpy)(2)Ru(Imdc)](-) (1(-)), where H(3)Imdc = imidazole-4,5-dicarboxylic acid and bpy = 2,2'-bipyridine. The optimized geometrical parameters for the complexes computed both in the gas phase and in solution are reported and compared with the previously reported X-ray data. The influence of pH on the absorption, emission, and redox properties of [(bpy)(2)Ru(H(2)Imdc)](+) (1(+)) has been thoroughly investigated. The absorption titration data were used to determine the ground state pK values, whereas the luminescence data were utilized for the determination of excited state acid dissociation constants. The proton-coupled redox activity of 1(+) has been studied over the pH range 2-12 in acetonitrile-water (3:2). From the E(1/2) versus pH profile, the equilibrium constants of the variously deprotonated complex species in Ru(II) and Ru(III) oxidation states have been determined. As compared to the protonated complex (1(+)), which undergoes reversible oxidation at 0.96 V (vs Ag/AgCl) in acetonitrile, the redox potential of the fully deprotonated complex (1(-)) is shifted to a much lower value, viz., 0.52 V. Density functional theory (DFT) and time-dependent DFT (TD-DFT) study provides insight into the nature of the ground and excited states with resulting detailed assignments of the orbitals involved in absorption and emission transitions. In particular, the red-shifts of the absorption and emission bands and the cathodic shift in the oxidation potential of 1(+) compared to 1 and 1(-) are also reproduced by our calculations.     

Structural characterization and spectroelectrochemical, anion sensing and solvent dependence photophysical studies of a bimetallic Ru(II) complex derived from 1,3-di(1H-imidazo[4,5-f][1,10]phenanthroline-2-yl)benzene

The X-ray crystal structure of a mixed-ligand bimetallic ruthenium(II) complex of composition [(bipy)(2)Ru(H(2)Impib)Ru(bipy)(2)](ClO(4))(4) (1), where H(2)Impib = 1,3-di(1H-imidazo[4,5-f][1,10]phenanthroline-2-yl)benzene and bipy = 2,2'-bipyridine, has been determined and showed that the compound crystallized in monoclinic form with the space group P2(1)/c. The absorption, steady state and time-resolved luminescence spectral properties of the complex were thoroughly investigated in different solvents. The compound displays strong luminescence at room temperature with lifetimes in the range of 140-470 ns, depending upon the nature of the solvent. Solvent-induced lifetime tuning makes the complex a suitable solvatochromic probe. The complex is found to undergo one simultaneous two-electron reversible oxidation in the positive potential window (0 to +1.6 V) and four quasi-reversible reductions in the negative potential window (0 to -2.2 V). Spectroelectrochemical studies have also been carried out for the bimetallic compound in the range of 300-1600 nm. With stepwise oxidation of the Ru(ii) centers replacement of MLCT bands by LMCT bands occur with the development of a broad band at λ(max) = 1260 nm, which is ascribed to inter-valence charge-transfer (IVCT) transition for the mixed-valence Ru(II)Ru(III) species. The anion sensing properties of the receptor were thoroughly investigated in acetonitrile solution using absorption, steady state and time-resolved emission spectroscopic studies. The anion sensing studies revealed that the receptor acts as sensor for F(-), AcO(-) and H(2)PO(4)(-). It is evident that in the presence of excess F(-) and AcO(-) ions, deprotonation of the imidazole N-H fragments of the receptor occurs, an event which is signaled by the change of color from yellow to orange visible to the naked eye. From the absorption and emission titration studies the binding/equilibrium constants of the receptor with the anions have also been determined. Anion-induced lifetime quenching by F(-) and AcO(-) and enhancement by H(2)PO(4)(-) makes the receptor a suitable lifetime-based sensor for selective anions. Cyclic voltammetry (CV) measurements of the compound carried out in acetonitrile have provided evidence in favor of anion-dependent electrochemical responses with F(-) and AcO(-) ions.     

Epitaxial Growth of Crystalline Polyaniline on Reduced Graphene Oxide

Due to its unique electronic properties, graphene has already been identified as a promising material for future carbon based electronics. To develop graphene technology, the fabrication of a high quality P‐N junction is a great challenge. Here, we describe a general technique to grow single crystalline polyaniline (PANI) films on graphene sheets using in situ polymerization via the oxidation‐reduction of aniline monomer and graphene oxide, respectively, to fabricate a high quality P‐N junction, which shows diode‐like behavior with a remarkably low turn‐on voltage (60 mV) and high rectification ratio (1880:1) up to a voltage of 0.2 V. The origin of these superior electronic properties is the preferential growth of a highly crystalline PANI film as well as lattice matching between the d‐values [∼2.48 Å] of graphene and {120} planes of PANI.

     

Monte Carlo study of the XY-model on Sierpinski gasket

We have performed a Monte Carlo study of the classical XY-model on two-dimensional Sierpinski gaskets (SGs) of several cluster sizes. From the dependence of the helicity modulus on the cluster size we conclude that there is no phase transition in this system at a finite temperature. This is in agreement with previous findings for the harmonic approximation to the XY-model on SG and is analogous to the absence of finite-temperature phase transition for the Ising model on fractals with a finite order of ramification.     

Adiabatic phase variation for optical Gaussons

This paper studies the adiabatic phase variation of optical Gaussons in the presence of perturbation terms. The modified conservation law of phase variation is used to carry out this analysis.