Fluorescence properties of photonic crystals doped with perylenediimide

This study aims to present the fabrication of colloidal photonic crystals (PC) with increased fluorescence properties. The use of a highly fluorescent perylenediimide derivate (PDI) during the soap-free emulsion polymerization of styrene-acrylic acid resulted in monodisperse core-shell particles which allowed the fabrication of PC films. The properties of the hybrid material were studied in comparison with hybrid materials obtained by impregnation of films with chromophore solutions. In both cases an increase of the fluorescence response was observed in addition to a blue shift for the PDI core particles, proving the incorporation of the dye inside the copolymer particles.     

Role of temperature in the physics of metallic clusters

The finite temperature of the ionic degrees of freedom plays either a determining or an important role in a large variety of cluster properties. We briefly review here the role played by the temperature in different cluster phenomena, such as: occurrence of phase transitions, shape fluctuations, detailed properties of the static and dynamic structure formfactors, of the electron single-particle spectra and of the optical response, and the emergence of the 1/f-noise in ionic dynamics. Presented at the International Conference on “Atomic Nuclei and Metallic Clusters”, Prague, September 1–5, 1997.     

Structural study of the influence of partially crystalline poly(ethylene butene) random copolymers on paraffin crystallization in dilute solutions

Random crystalline–amorphous copolymers containing ethylene and butene segments, yielded from dilute-solution, and self-assembled to one-dimensional, needle-shaped aggregates, can modify wax crystal structures through the cocrystallization of the copolymer and wax molecules into hairy platelets. These copolymers show selectivity in their wax crystal modification capacities that depends on the ethylene content of the backbone. Thus, it has been qualitatively established that a copolymer containing larger crystallizable polyethylene sections [poly(ethylene butene) with 7.5 ethyl branches per 100 backbone carbons (PEB-7.5)] is very efficient for longer wax molecules (C₃₆), whereas for shorter waxes (C₂₄), its efficacy diminishes. Here we present a quantitative evaluation of the small-angle neutron scattering results obtained in a complex study of the self-assembling behavior of PEB-7.5 and paraffin waxes (C₂₄ and C₃₆) in decane and of cocrystallization for different polymer–paraffin combinations and solution conditions. The richness of the morphologies was evaluated with a contrast variation technique and the application of structural models. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3113–3132, 2004     

Quantum transport in complex systems

We derive the influence function and the effective dynamics of a quantum systems coupled to a chaotic environment, using very general parametric and banded random matrices to describe the quantum properties of a chaotic bath. We find that only in certain limits the thermalization can result from the environment. We study the general transport problems including escape, fusion and tunneling (fission). Presented by D. Kusnezov at the International Conference on “Atomic Nuclei and Metallic Clusters”, Prague, September 1–5, 1997.     

Photonic crystals obtained by soap-free emulsion terpolymerization

This paper presents the use of soap-free emulsion terpolymerization to obtainphotonic crystals (PCs). Monodisperse latexes resulted from the polymerization of styrene (ST) with 2-hydroxyethyl methacrylate (HEMA) and acrylic acid (AA) at different compositions defined as system A, B and C respectively. The water solubility of the macroradicals determined different nucleation mechanisms in all three cases. The micellar nucleation mechanism was more predominant for generating system A, whereas the homogeneous nucleation was specific for system C. For system B, both nucleation mechanisms werepossible with the same probability. The latexes and the resulted PCs were characterized by optical microscopy (OM), dynamic light scattering (DLS), gel permeation chromatography (GPC) and UV-VIS spectroscopy.      

New conjugates of calix[4]arenes bearing dipyridine and indolizine heterocycles

A simple route to introduce various heterocycles, derivatives of dipyridyls and indolizines on the lower rim of the para-tert-butylcalix[4]arene via ester bond formation to afford 1,3-disubstituted conjugates is described. The conformation of the new compounds and some intermolecular interactions are discussed on the basis of X-ray and NMR analyses. Preliminary complexation properties of some of the new tert-butylcalix[4]arene heterocyclic conjugates with Cu (II), Co (II) and Ni (II) were studied by means of UV–Vis titration.     

Synthesis,characterization and catalytic activity of halo-methyl-bis(salicylaldehyde)ethylenediamine cobalt(II) complexes

The synthesis, characterization and catalytic activity of a series of tetra-halo-dimethyl salen and di-halo-tetramethyl-salen ligands are reported in this paper: α,α′-dimethyl-Salen (dMeSalen) (L¹); 3,3′,5,5′-tetrachloro-α,α′-dimethyl-Salen, (tCldMeSalen) (L²); 3,3′-dibromo-5,5′-dichloro-α,α′-dimethyl-Salen, (dCldBrdMeSalen) (L³); 3,3′,5,5′-tetrabromo-α,α′-dimethyl-Salen, (tBrdMeSalen) (L⁴); 3,3′,5,5′-tetraiodo-α,α′-dimethyl-salen, (tIdMeSalen) (L⁵); 3,3′-dichloro-5,5′,α,α′-tetramethyl-Salen (dCltMeSalen) (L⁶); 3,3′-dibromo-5,5′,α,α′-tetramethyl-Salen (dBrtMeSalen) (L⁷); and 3,3′-diiodo-5,5′,α,α′-tetramethyl-Salen (dItMeSalen) (L⁸) (Salen = bis(salicylaldehyde)ethylenediamine). Upon reaction with Co(II) ions, these ligands form complexes with square planar geometry that have been characterized by elemental analysis, cyclic voltammetry, UV–Vis, IR and EPR spectroscopies. In the presence of pyridine the obtained Co(II) complexes were found able to bind reversibly O₂, which was shown by EPR spectroscopy and cyclic voltammetry. They were also found able to catalyze the oxidation of 2,6-di-tert-butylphenol (DtBuP) (9) with formation of 2,6-di-tert-butyl-1,4-benzoquinone (DtBuQ) (10) and 2,6,2′,6′-tetra-tert-butyl-1,1′-diphenobenzoquinone (TtBuDQ) (11). These properties are first influenced by the coordination of pyridine in axial position of the Co(II) ion that causes an increase of the electronic density on the cobalt ion and as a consequence a decrease in the E_1/2 value and an increase of the reducing power of the Co(II) complex. It is noteworthy that, under those conditions the complexes also show a remarkable quasi-reversible behaviour. Second, complex properties are also influenced by the substituents (methyl and halogen) grafted on the aromatic ring and on the azomethynic groups. The donating methyl substituent on the azomethynic groups causes a decrease in the E_1/2 value, whereas the halogen substituents on the aromatic rings have two effects: a mesomeric donating effect that tends to lower the redox potential of the complex, and a steric effect that tends to decrease the conjugation of the ligand and then to increase the redox potential of the Co(II) complex. In pyridine, the steric effect predominates, which causes both an increase of the redox potential and a decrease of the selectivity of the oxidation of phenol 9. As a result of all these effects, it then appears that the best catalysts to realize the selective oxidation of 2,6-di-tert-butyl-phenol (9) by O₂ are the Co complexes of ligands bearing CH₃ donating substituents, Co(dMeSalen) 1 (2CH₃ substituents), and Co-di-halo-tetra-methyl-salen complexes 6, 7 and 8 (4CH₃ substituents), in the presence of pyridine.     

Harmonic approximation on arcs

If a real interval is mapped by a continuous, proper injection into a noncompact Riemannian manifold of dimension at least two, then every continuous function on the image arc can be approximated arbitrarily closely by functions harmonic on the entire manifold.