Antonio Roviello

Light-induced spiral mass transport in azo-polymer films under vortex-beam illumination

When an azobenzene-containing polymer film is exposed to non-uniform illumination, a light-induced mass migration process may be induced, leading to the formation of relief patterns on the polymer-free surface. Despite many years of research effort, several aspects of this phenomenon remain poorly understood. Here we report the appearance of spiral-shaped relief patterns on the polymer film under the illumination of focused Laguerre–Gauss beams with helical wavefronts and an optical vortex at their axis. The induced spiral reliefs are sensitive to the vortex topological charge and to the wavefront handedness. These findings are unexpected because the doughnut-shaped intensity profile of Laguerre–Gauss beams contains no information about the wavefront handedness. We propose a model that explains the main features of this phenomenon through the surface-mediated interference of the longitudinal and transverse components of the optical field. These results may find applications in optical nanolithography and optical-field nanoimaging.

Discotic mesomorphism of 2,3,7,8,12,13,17,18-octakis (alkyl-thio) 5,10,15,20 tetraaza porphyrin and its complexes with some divalent transition metal ions Synthesis and characterization

Abstract New discotic metallomesogens of 2,3,7,8,12,13,17,18-octakis (alkyl-thio) 5,10,15,20 tetraaza porphyrin (H2Pn) and some related complexes, obtained by reaction of first row transition metal ions Ni(II), Co(II), Cu(II), Zn(II) with the free porphyrin, have been prepared. All materials were characterized by DSC measurements and optical observations. The microscopic structure of all mesophases was checked and characterized by X-ray diffraction. Except for H2P(7–12), all of the compounds are mesogenic; a few of them exhibit mesomorphic polymorphism. Melting (C→D) temperatures range from 40 to 85°C. Only NiP4, CoP4 and CuP4 show higher values. Both temperature and ΔH of isotropization (D→I) show a regular trend with respect to the number of carbon atoms in the alkyl chains and of the nature of the metal. ΔH values for complexes with partially filled d-shell metals are very similar and show definite differences with respect to those of Zn(II). Optical and X-ray data in the case of n  7 indicate a colum...

Thermotropic Mesomorphism in Some Cu(II) and Pd(II) Metallorganic Complexes

Abstract The synthesis and liquid crystal properties of some bis(N-p-(n-alkoxy)phenyl, p-(n-alkoxy)salicylaldiminato)copper(II), of a homologous series of bis(N-p-(n-alkanoyloxy)phenyl, p-(n-alkanoyloxy)salicylaldiminato)copper(II), and of some corresponding palladium(II) complexes are reported. All of the compounds examined exhibit enantiotropic smectic mesomorphism, predominantly of the C type. Palladium(II) complexes are mesomorphic up to higher temperatures than the copper(II) homologues.

Disc-like Mesogens: Synthesis and Characterization of a Series of Rufigallol-hexa-n-alkanoates

Abstract Aliphatic esters of rufigallol with formula have been prepared and their phase transitions studied by differential scanning calorimetry, x-ray diffraction, and optical methods. Compounds with 6 < m < 13 give enantiotropic columnar mesophases; those with 7 < m < 9 give also a monotropic mesophase. Both melting temperature and entropy are sensitive to the parity of the number of atoms contained in the flexible part of the molecules. No similar effect is present at the isotropization transition. Calorimetric data relative to the phase transitions, x-ray and optical patterns of the liquid crystalline phases are shown.

Two-photon patterning of a polymer containing Y-shaped azochromophores

We report on the patterning of the free surface of azo-based polymer films by means of mass migration driven by one- or two-photon absorption. A symmetric donor-acceptor-donor structured Y-shaped azochromophore is specifically synthesized to enhance two-photon absorption in the polymer. The exposure of the polymer film to a focused laser beam results in light-driven mass migration for both one- and two-photon absorptions. Features with subdiffraction resolution (250 nm) are realized and the patterning dynamics is investigated as a function of the light dose. Furthermore, functional photonic structures, such as diffraction gratings with periods ranging between 0.5 and 2.0 μm, have been realized.

Nematic and smectic mesophases in a new series of Cu(II) organometallic complexes

Abstract The synthesis and the phase behaviour of a homologous series of copper, bis[N-[[4-[4-(alkoxy)benzoyloxy],2-hydroxyphenyl]methylene]-methanamino] complexes is reported. They all exhibit thermotropic mesomorphism. The thermal stability range of the mesophase decreases slightly with increasing length of the alkoxy terminals. With the onset of smectic mesomorphism, for alkoxy groups containing ten carbon atoms, the stability interval of the nematic phase decreases progressively so that the compound containing 14 carbon atoms in the alkoxy terminal chains exhibits only smectic mesomorphism. Optical texture analysis suggests the smectic C nature of the phase in all cases. The enthalpies for the liquid crystal-isotropic transition have been measured and they are comparatively low. Remarkably low values have also been measured for the melting enthalpies of the smectogenic members of the series. These are associated with solid phase polymorphism which is discussed briefly.

New NLO active cyclopalladated chromophores in main-chain polymers

Abstract Four new OH-functionalized orthopalladated complexes bearing an electron-donor and an acceptor group in a trans -like arrangement with respect to the metal have been prepared and characterized. The ligands are Schiff bases, bound as C,N- or N,O-chelating moieties. Four new polyesters were obtained by polycondensation from the monomeric complexes and pentyloxyterephthaloyl chloride. Two “model” complexes, each one related to one monomer, were also synthetized, in order to obtain further and more detailed characterization data, and in particular to perform measurements of μβ .

A series of compounds forming polar crystals and showing single-crystal-to-single-crystal transitions between polar phases

Condensation of 4-hydroxybenzohydrazide with a variety of non-chiral aliphatic ketones, methylethylketone, acetone, cyclohexanone and cyclobutanone, affords imine compounds crystallizing in polar space groups (Pna21 or Cc). For all the compounds synthesized, the crystal structure was determined by single crystal X-ray analysis and second harmonic generation experiments were performed on powder samples. The imine obtained using acetone shows solid state polymorphism with unusual behaviour; three different crystal phases have been identified (phases I, II and III), all having the same polar space group Pna21, and the transitions from I to II and from III to II are topotactic, i.e. single-crystal-to-single-crystal. During the irreversible transition from phase I to II, the polar axis undergoes a strong compression (about 15%) and single crystals of the parent phase are violently shattered into single crystal fragments of the new phase, while in the reversible transition from phase III to II, the polar axis expands (about 14%) and the integrity of single crystals is preserved.

Crystal structure of a mesogenic copper(II) square-planar complex bis[N-p-(n-Hexyloxy)phenyl, p-(n-heptyloxy)salicylaldiminato] copper(II)

Abstract The crystal structure of this compound, a substance which exhibits smectic meso-morphism, is triclinic, P 1 space group, with lattice constants a = 11.280(5) A, b = 13.598(1) A, c = 25.650(2) A, α = 97.85(1) A, β = 96.76(3)° and γ = 100.37(3)°. Molecules with two different conformations are present in the unit cell, and the heptyl and hexyl side-chains are extended nearly parallel to each other. The molecules are packed together in layers with their major axes inclined at 60° to the layer plane. The observed structure explains why the liquid crystal mesophases of this and related compounds are not discotic.

Discotic mesomorphism of rufigallol hexa-n-alkoxylates

Abstract Aliphatic ethers of rufigallol have been prepared and their discotic mesomorphism studied. All the compounds give enantiotropic, columnar mesophases with a regular stacking of the discs along the columns, as revealed by the X-ray diffraction patterns of the mesophases. Calorimetric data indicate a wide range of stability of the mesophase. Solid polymorphism has been demonstrated that involves both solution crystallized and melt crystallized samples.