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.

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

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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 columnar mesophase with hexagonal packing whereas in complexes with n < 7 the observed mesophase shows a non-hexagonal columnar packing. CuP6 and NiP6 probably show both mesophases which are connected by a phase transition, presumably of second order or with exceedingly low enthalpy change but easily detected by polarizing microscopy because of sharp texture changes. As expected, no odd–even effect is detectable on the properties of the liquid-crystalline phases as a function of the number of carbon atoms in the aliphatic chains

Semiflexible mesophasic polymers of the general formula +OOC(CHz),-2-COO-R' + , n = 9, 11, 13, where R' = -C,H5-C(CH3)zlCH-C6H5-and R2 = C6H+(CH3)=N-N=(CH3)C-C6H5are prepared and their solid and liquid crystalline behaviour examined and compared to that of the corresponding homologues with n even. Evidence is given of relevant oddeven effects in the thermodynamic parameters of the clearing transition. The conclusion is drawn in favour of an anisotropic structuration also of the flexible parts of the polymer chain in the liquid crystal phase. n = 9, 11, 13, +OOC(CHz),~z-COO-R2+, n = 9, 11, 13, 14, and +OOCO-(CHz),-,