Unusual Excited State Characteristics of 6-aminobenzothiazole with β-cyclodextrin

The interaction between 6-aminobenzothiazole (6ABT) and β-cyclodextrin (β-CDx) has been investigated in solution and solid state. The stoichiometry and binding constants of the complex between 6ABT and β-CDx in solution have been determined by steady state and time-resolved fluorescence spectroscopy. Fluorescence intensity of neutral form decreases during complexation which is contrary to the usual observation. This is explained by hydrogen bonding interaction between lone pair of nitrogen with OH groups of β-CDx. The FT-IR spectral study and SEM images of solid complex confirmed the formation of inclusion complex. Excited state acidity constants for 6ABT have been determined in aqueous and β-CDx medium and discussed.     

A Facile Solid‐Phase Route to Renewable Aromatic Chemicals from Biobased Furanics

Renewable aromatics can be conveniently synthesized from furanics by introducing an intermediate hydrogenation step in the Diels–Alder (DA) aromatization route, to effectively block retro‐DA activity. Aromatization of the hydrogenated DA adducts requires tandem catalysis, using a metal‐based dehydrogenation catalyst and solid acid dehydration catalyst in toluene. Herein it is demonstrated that the hydrogenated DA adducts can instead be conveniently converted into renewable aromatics with up to 80 % selectivity in a solid‐phase reaction with shorter reaction times using only an acidic zeolite, that is, without solvent or dehydrogenation catalyst. Hydrogenated adducts from diene/dienophile combinations of (methylated) furans with maleic anhydride are efficiently converted into renewable aromatics with this new route. The zeolite H‐Y was found to perform the best and can be easily reused after calcination.     

Effect of complexing agent (1,10-phenanthroline) on ADP and KDP crystals

1,10-Phenanthroline (Phen) as a new additive was added into the solutions of KH₂PO₄ (KDP) and NH₄H₂PO₄ (ADP) in a small amount (∼2.5·10⁻³ M L⁻¹). The crystals were grown from the aqueous solutions of pH ∼4.5 at constant temperature by solvent evaporation technique. It leads to an increase in metastable zone width and assists the bulk growth process. The growth rate of crystals in the presence of Phen decreases considerably with an increase in impurity concentration (∼2.5·10⁻² M L⁻¹). Not much variation is observed in FTIR and XRD of pure and doped ADP/KDP. It appears that the growth promoting effect (GPE) of Phen is caused by the adsorption of the organic additive on the prism faces of ADP/KDP crystals. Higher optical transmittance is observed in the presence of the dopant. Detailed microhardness studies of ADP crystals reveal the anisotropy in the hardness behaviour. Scanning electron microscope (SEM) photographs exhibit the effectiveness of the impurity in changing the surface morphology of ADP/KDP crystals. Contrary to expectations, Phen depresses the NLO efficiency of ADP/KDP, suggesting that the molecular alignments in the presence of Phen results in cancellation effects disturbing the non-linearity.     

Chiral building blocks from biomass: 2,5-diamino-2,5-dideoxy-1,4-3,6-dianhydroiditol

An efficient route towards the synthesis of 2,5-diamino-2,5-dideoxy-1,4-3,6-dianhydroiditol 4 has been developed resulting in significant improvements in both isolated yields and purity when compared to literature procedures. As a consequence, resin-grade 2,5-diamino-2,5-dideoxy-1,4-3,6-dianhydroiditol 4 has become available for laboratory scale step-growth polymer synthesis. Additionally, an interesting renewable chiral 2-amino-2-deoxy-1,4-3,6-dianhydroiditol 10, has been isolated.     

Pressure-induced colossal piezoresistance effect and the collapse of the polaronic state in the bilayer manganite (La(0.4)Pr(0.6))(1.2)Sr(1.8)Mn2O7

We have investigated the effect of hydrostatic pressure as a function of temperature on the resistivity of a single crystal of the bilayer manganite (La(0.4)Pr(0.6))(1.2)Sr(1.8)Mn(2)O(7). Whereas a strong insulating behaviour is observed at all temperatures at ambient pressure, a clear transition into a metallic-like behaviour is induced when the sample is subjected to a pressure (P) of ~1.0 GPa at T < 70 K. A huge negative piezoresistance ~10(6) in the low temperature region at moderate pressures is observed. When the pressure is increased further (5.5 GPa), the high temperature polaronic state disappears and a metallic behaviour is observed. The insulator to metal transition temperature exponentially increases with pressure and the distinct peak in the resistivity that is observed at 1.0 GPa almost vanishes for P > 7.0 GPa. A modification in the orbital occupation of the e(g) electron between 3d(x(2)-y(2)) and 3d(z(2)-r(2)) states, as proposed earlier, leading to a ferromagnetic double-exchange phenomenon, can qualitatively account for our data.     

Crystal growth,structure and characterization of p-Toluidinium picrate

p-Toluidinium picrate (PTP), is a proton transfer complex of 2,4,6-trinitrophenol as an electron acceptor with p-toluidine as electron donor, crystallizing in the monoclinic system with four molecules in the unit cell (space group P2₁/c). The vibrational patterns of the organic crystal PTP in comparison with that of the parent compound clearly evidences the complex formation. Loss of hydroxyl proton at O1 leading to specific electron delocalization around C1 is observed. Crystallographic data are reported as a=12.9304(6)  Å, b=15.7176(7)  Å, c=7.5403(4)  Å, β=101.837(5)°. The crystalline cohesion is achieved by N–H…O and C–H…O hydrogen bonds and the ions are linked into three dimensional network. Intermolecular hydrogen bonding between nitrogen of p-toluidine and phenolate ion of picric acid results in charge transfer. A sharp endotherm in the DSC curve, no decomposition up to the melting point and poor absorbance in the visible region indicate the suitability of the material for potential applications.     

Synthesis,characterization, crystal structure and NLO properties of a new mixed crystal potassium sodium ammonium dihydrogenphosphate K0.23Na0.23(NH4)0.54H2PO4

Potassium sodium ammonium dihydrogenphosphate K_0.23Na_0.23(NH₄)_0.54H₂PO₄ (KSADP), a new mixed crystal has been grown in aqueous medium by the slow evaporation of equimolar mixture of ammonium dihydrogenphosphate (ADP), potassium dihydrogenphosphate (KDP) and sodium dihydrogenphosphate (SDP). Crystal composition as determined by single crystal X-ray diffraction analysis reveals that it belongs to the tetragonal system with noncentrosymmetric space group I-42d and it is structurally similar to ADP with cell parameter values, a=7.4794(4) Å; b=7.4794(4) Å; c=7.2974(11) Å; υ=408.23(7) Å³; z=4. The presence of sodium and potassium in ADP matrix was confirmed by inductively coupled plasma emission spectrometry and energy dispersive X-ray spectroscopy. The partial cationic substitution results in defect centers influencing the physical properties. Slight shifts in vibrational patterns could be attributed to strains in the lattice. Refinement of structure by single crystal XRD analysis reveals that potassium, sodium and ammonium coexist in the mixed crystal. The surface morphology of the as-grown specimen, which is changed as a result of cationic incorporation, was studied by scanning electron microscopy. The relative second harmonic generation (SHG) efficiency measurements revealed that the mixed crystal has a superior NLO activity than ADP.     

UV excitable Y2? x ? y Gd y SiO5:Ce x phosphors for cool white light emission

Cool white light was realized in Y_2−x−y Gd _x SiO₅: Ce _y phosphor under near UV excitation, due to the occupation Ce³⁺ in Y³⁺ 1st and 2nd site, synthesized using solid state carbothermal reduction route. SEM with elemental analysis show the existence of Gd in Y₂SiO₅:Ce enhances the particles size in comparison to Y₂SiO₅:Ce phosphors alone. Gd³⁺ (0.00≤x≤0.75) and Ce³⁺ (0.02≤y≤0.10) concentration was optimized to 0.50 and 0.08 in Y₂SiO₅, respectively. The CIE chromaticity color coordinates (0.24, 0.20) are close to cool white light value which could be useful for the fabrication of cool white LED.     

Enhancement of second harmonic generation efficiency: Growth and characterization of magnesium(II)-doped tetrakis(thiourea)nickel(II) chloride crystals

The influence of magnesium doping on the properties of tetrakis(thiourea)nickel(II) chloride crystals has been described. The reduction in the intensity observed in powder X-ray diffraction of doped specimen and slight shifts in vibrational frequencies confirm the lattice stress as a result of doping. Surface morphological changes due to doping of the alkaline earth metal are observed by scanning electron microscopy. The incorporation of Mg(II) into the crystal lattice was confirmed by energy dispersive X-ray spectroscopy. Lattice parameters are determined by single crystal XRD analysis. The thermogravimetric and differential thermal analysis studies reveal the purity of the materials and no decomposition is observed up to the melting point. The crystal is further characterized by Kurtz powder technique and dielectric studies.