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.

Dye sensitized solar cells (DSSC) are considered one of the most promising photovoltaics technologies alternative to the traditional silicon based solar cells because of their compatibility with low cost manufacture methodologies, their peculiar optical and mechanical properties and their high indoor efficiency. Photosensitizers represent one of the most important part in a DSSC device and probably the most thoroughly investigated in the last twenty years, with thousands of dyes that have been proposed and tested for this kind of application. In this review we aimed to give an overview of the three main classes of DSSC photosensitizers, namely ruthenium (II) polypyridyl complexes, Zn-porphyrin derivatives and metal free organic dyes. After a brief introduction on the architecture and operational principles of a DSSC and on the state of the art of the other main components of this kind of device, we focused our discussion on photosensitizers. We defined the several requirements DSSC photosensitizers should fulfil and provided an excursus about their historical development along the years; by examining specific dyes reported in the literatures, we attempted to highlight the molecular design strategies that have been established for the optimization of their performance in actual devices both for what concerns efficiency (that recently reaches an outstanding 14.3 %) and operational stability. We finally discussed, in the last section, about the possible future developments of this intriguing technology.

The ability of thermosalient solids, organic analogues of inorganic martensites, to move by rapid mechanical reconfiguration or ballistic event remains visually appealing and potentially useful, yet mechanistically elusive phenomenon. Here, with a material that undergoes both thermosalient and non-thermosalient phase transitions, we demonstrate that the thermosalient effect is preceded by anomalous thermal expansion of the unit cell. The crystal explosion occurs as sudden release of the latent strain accumulated during the anisotropic, exceedingly strong expansion of the unit cell with α_a = 225.9 × 10⁻⁶ K⁻¹, α_b = 238.8 × 10⁻⁶ K⁻¹ and α_c = −290.0 × 10⁻⁶ K⁻¹, the latter being the largest negative thermal expansivity observed for an organic compound thus far. The results point out to the occurence of the thermosalient effect in phase transitions as means to identify new molecular materials with strong positive and/or negative thermal expansion which prior to this work could only be discovered serendipitously.