Anion induced modulation of self-assembly and optical properties in urea end-capped oligo(p-phenylenevinylene)s

The non-emissive supramolecular assembly of urea end-capped oligo(p-phenylenevinylene) flourophores turned strongly emissive in the presence of tetrabutylammonium flouride which has implications in the anion controlled design of supramolecular architectures with tunable emission properties.     

Photoresponsive soft materials: Synthesis and photophysical studies of a stilbene‐based diblock copolymer

An amphiphilic diblock copolymer composed of a photoresponsive dialkoxycyanostilbene polymethacrylate and poly(ethylene oxide) (PDACS‐b‐PEO) was synthesized and its photophysical and aggregation properties were investigated. The amphiphilic nature of the polymer caused it to self‐assemble in water, and dynamic light scattering studies indicated formation of spherical aggregates with an average size of 160 nm. Atomic force microscopy images of dried films cast from solutions containing the polymer aggregates revealed supramolecular aggregates with a spherical morphology. Photoisomerization of the stilbene chromophore in PDACS‐b‐PEO on UV irradiation resulted in the destruction of the self‐assembled superstructures which could be attributed both to change in shape of the chromophore from the linear trans isomer to the bent cis isomer which would hinder self‐aggregation of the molecules and the higher dipole moment of the cis isomer leading to a reduction of the hydrophobic nature of the stilbene containing block of PDACS‐b‐PEO. It was observed that hydrophobic dyes such as curcumin could be encapsulated within the hydrophobic interior of the spherical micellar aggregates from which the encapsulated dye could be released on UV irradiation. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Harmonic Cheeger–Simons characters with applications

We initiate the study of harmonic Cheeger–Simons characters, with applications to smooth versions of the Geometric Langlands program in the abelian case.     

FT-IR, FT-Raman and FT-SERS spectra of 4-aminosalicylic acid sodium salt dihydrate.

FT-IR, FT-Raman and FT-SERS spectra of 4-aminosalicylic acid sodium salt dihydrate (4ASAS) have been recorded and analysed. The vibrational bands due to NH2, OH, carboxyl group, and the benzene ring are identified. The CX ipb(17a, 17b), CC ipb(6,18a) and CH ipb (3,14a, 14b) bands are more enhanced in SERS. Broadening of the inplane carboxyl bend indicates interaction with the silver surface. Further the vC=O, v(C-O)c and v(C-O)h are intense in the SERS spectrum. The rocking and wagging modes of NH2 also show up in SERS. The molecule (O, N donor ligand) is thought to adsorb through the carboxyl oxygen atom with the benzene ring in a 'perpendicular side on orientation' with respect to the silver surface.     

Spectroscopic investigations and computational study of sulfur trioxide–pyridine complex

The Fourier transform infrared (FT‐IR) and FT‐Raman spectra of sulfur trioxide‐pyridine complex were recorded and analyzed. The potential‐dependent surface‐enhanced Raman scattering (SERS) was recorded from an electrochemically roughened silver electrode. The vibrational wave numbers of the compound were computed using the Hartree–Fock/6‐31G* basis and compared with the experimental values. The presence of strong pyridine ring vibrations in the SERS spectrum reveals the interaction between the pyridine ring and the silver surface. The molecule is adsorbed on the silver surface with the pyridine ring in a tilted orientation. The direction of charge‐transfer contribution to the SERS is discussed from the frontier orbital theory. The value of the calculated first hyperpolarizability is comparable to those reported for similar structures, which makes this molecule an attractive object for future studies of nonlinear optics. The optimized geometrical parameters of the title compound are in agreement with similar reported structures. Copyright © 2011 John Wiley & Sons, Ltd.     

Stable hydrosols for TiO<Subscript>2</Subscript> coatings

The optimum processing parameters required to synthesize, by hydrolysis of titanium isopropoxide (TIP), highly stable hydrosols composed of nanoparticles of the smallest possible size, are deduced both from data available in literature and from our own experiments. The colloids prepared in these conditions are composed of aggregates of anatase (~90%) and brookite crystallites (5–6 nm). They are suitable for coatings and have long-term stability (more than one year) in terms of polymorphic composition, crystallite and agglomerate size. Stable sols composed solely of anatase crystallites (4 nm) can be prepared by partially complexing the TIP by acetylacetone before hydrolysis. It is not possible to produce porous films with these colloids because they are stabilized by electrostatic repulsion which causes the particles to organize themselves, during the drying step, to form materials with a close packed structure. However, coatings with controlled porosity can be prepared from these stable sols through the post addition of polymers, like PEG or block copolymers.     

Non‐covalent Versus Covalent Control of Self‐Assembly and Chirality of Nile Red‐modified Nucleoside and DNA

A DNA‐based covalent versus a non‐covalent approach is demonstrated to control the optical, chirooptical and higher order structures of Nile red ( Nr ) aggregation. Dynamic light scattering and TEM studies revealed that in aqueous media Nr ‐modified 2′‐deoxyuridine aggregates through the co‐operative effect of various non‐covalent interactions including the hydrogen bonding ability of the nucleoside and sugar moieties and the π‐stacking tendency of the highly hydrophobic dye. This results in the formation of optically active nanovesicles. A left‐handed helically twisted H‐type packing of the dye is observed in the bilayer of the vesicle as evidenced from the optical and chirooptical studies. On the other hand, a left‐handed helically twisted J‐type packing in vesicles was obtained from a non‐polar solvent (toluene). Even though the primary stacking interaction of the dye aggregates transformed from H→J while going from aqueous to non‐polar media, the induced supramolecular chirality of the aggregates remained the same (left‐handed). Circular dichroism studies of DNA that contained several synthetically incorporated and covalently attached Nr ‐modified nucleosides revealed the formation of helically stacked H‐aggregates of Nr but—in comparison to the noncovalent aggregates—an inversed chirality (right‐handed). This self‐assembly propensity difference can, in principle, be applied to other hydrophobic dyes and chromophores and thus open a DNA‐based approach to modulate the primary stacking interactions and supramolecular chirality of dye aggregates.