Networking of calixcrowns: from heteronuclear endo/exocyclic coordination polymers to a photoluminescence switch

Solvato-PL switching and shrinking-and-opening process: we present two CuI coordination polymers of calix[4]-bis-monothiacrown (L) obtained in the absence (1) and presence (2) of KI. The structures show not only very unusual CuI-based network arrangements but also unique reversible photolunimescence switching behavior induced by removal of coordinated solvent. Furthermore, upon inclusion of K+ ions the crown ring shrinks leading to "opening" of opposite aromatic rings in the host calixarene unit, rare behavior for this class of compound.     

Temperature-dependent 3-D CuI coordination polymers of calix[4]-bis-dithiacrown: crystal-to-crystal transformation and photoluminescence change on coordinated solvent removal

The temperature-dependent assembly of two 3-D CuI coordination polymers containing calix[4]-bis-thiacrown with different networking motifs are reported. Upon removal of the coordinated solvent molecules the initial solvent-coordinated polymer undergoes a unique single-crystal-to-single-crystal transformation to the desolvated polymer. Structural characteristics observed in the solvent-coordinated and the desolvated polymers also reveal related solvato-photolunimescence "off-on" behavior.     

Vibrational and gravimetric analysis of polyaniline/polysaccharide composite materials

In this paper, we present a comparative study of polyaniline/polysaccharide composites (starch, carboxymethyl cellulose, cellulose acetate, and chitosan) by FTIR, UV-visible, SEM and electrochemical analysis. We propose that simultaneously three different phenomena happen while formation of composite system that may be listed as degradation of polysaccharide, polymerization of aniline, formation of polyaniline- polysaccharide composite. Effects of hydrochloric acid and oxidizing agent (ammonium peroxydisulphate) on the structure of polysaccharides were also investigated. We obtained dissimilar product yield and variable polyaniline and polysaccharide ratio in the composite system even though experimental conditions were same. The possible reasons responsible for the observed differences as well as characteristics and morphology of protonated and deprotonated composite materials are discussed.     

Calix[4]bis(thiacrown): assembly of an endocyclic disilver(I) complex and exocyclic 3D copper(I) coordination polymers

Calix[4]bis(thiacrown-5) (L) with 1,3-alternating conformation was employed as a strong dinucleating ligand for the soft metal ions AgI and CuI. The reaction of L with AgPF6 afforded a discrete endo-coordinated disilver(I) complex 1, [Ag2L](PF6)2. In contrast, mixed products (2a + 2b) consisting of 3D networks were obtained from the reaction of L and CuI; 2b linked with a Cu4I4 cubane unit was shown to generate photoluminescence, while 2a linked with a Cu2I2 rhomboid unit does not.     

Infrared Divergences in Light Front Field Theory and Coherent State Formalism

We discuss fermion self energy correction in light front QED using a coherent state basis. We show that if one uses coherent state basis instead of fock basis to calculate the transition matrix elements the true infrared divergences in δ m ² get canceled up to O(e ⁴). We show this in Light-front as well as in Feynman gauge.     

Photoinduced processes of newly synthesized bisferrocene- and bisfullerene-substituted tetrads with a triphenylamine central block

Photoinduced electron transfer processes of two newly synthesized tetrads with a triphenylamine (TPA) as central building block, to which bisfullerenes (C₆₀) and bisferrocenes (Fc) are covalently connected, have been studied. One of them has a TPA linked with one C₆₀ moiety and two ferrocene moieties C₆₀-TPA-(Fc)₂ and another tetrad has a TPA linked with two C₆₀ moieties and one ferrocene unit (C₆₀)₂-TPA-Fc. The photophysical properties of (C₆₀)_m-TPA-(Fc)_n have been investigated by applying the picosecond time-resolved fluorescence and nanosecond transient absorption techniques in both polar and nonpolar solvents. The charge separation process via the excited singlet state of the C₆₀ moiety of the C₆₀-TPA-(Fc)₂ is more efficient than that of the (C₆₀)₂-TPA-Fc. It is found that the ratio of Fc-donor to C₆₀-acceptor affects charge separation efficiency via the excited singlet state of the C₆₀ moiety.     

First synthesis and determination of the absolute stereochemistry of iso-cladospolide-B and cladospolides-B and C

The syntheses of iso-cladospolide-B, cladospolide-B and cladospolide-C are reported with 4S,5S,11S-configuration. Of the three stereogenic centres, the C-4/C-5 vic-diol was created by Evans aldol condensation, while the C-11 stereocentre was created by Jacobsen’s method. The synthesis of cladospolides 1-3 defined the absolute stereochemistry of these natural products.     

Arbitrary oscillatory Stokes flow past a porous sphere using Brinkman model

The present paper deals with the hydrodynamics of a porous sphere placed in an arbitrary oscillatory Stokes flow. Unsteady Stokes equation is used for the flow outside the porous sphere and Brinkman equation is used for the flow inside the porous sphere. Corresponding Faxén’s law for drag and torque is derived and compared with few existing results in some special cases. Examples like uniform flow, oscillatory shear flow and oscillating Stokeslet are discussed. Also, translational oscillation of a weakly permeable sphere is discussed.