Luisa Raimondo

Thanks to the commercial success of organic light-emitting diodes, organic electronics is now much more than just a niche alternative to traditional electronics. However, other types of devices based on organic semiconductors (OSCs) are still far from market readiness. A key limitation is that, in thin-film form, OSCs exhibit a high level of structural disorder. Of all strategies for growing films of OSCs, those relying on organic epitaxy yield films whose properties most closely resemble those of single crystals. Yet, this comes at a cost: conventional substrates for epitaxial growth are incompatible with practical device integration. To overcome this issue, we introduce a transfer printing method capable of relocating epitaxially grown films of OSCs from their native substrates to target, device-compatible ones. We demonstrate the feasibility of this approach by transferring highly crystalline rubrene films─grown via organic molecular beam epitaxy and characterized by coherently oriented, micrometer-scale domains and single-crystal-like optical response─from amino acid single crystals to technologically relevant substrates. Notably, morphology, optical characteristics, and photoluminescence dynamics of the films are fully retained following transfer.

The results obtained using laboratory and transportable XRF and RS instruments to analyze metal ingots discovered from a Roman shipwreck are compared to assessing the possibility of in situ analyses.

Starch-cinnamyl ethers are synthesized, shaped into thin films and characterized for their ability to undergo photo crosslinking.

Insights for an effective evaluation of copper exsolution in Cu-doped SrTiO ₃ have been obtained by combining classical techniques with EPR.

Crystalline rubrene (RUB) in the orthorhombic structure can be regarded as a workhorse in organic optoelectronics. So far, however, its great potential for device integration has been held back by the struggle to obtain high quality and photo-oxidation resistant RUB thin films. Here, we propose an effective strategy to obtain homogeneous, highly crystalline, and oriented RUB thin films, which relies on a spontaneous amorphous-to-crystal transition driven by organic epitaxy occurring at room temperature in vacuum: this crucial process dictates the final morphological, structural, and optoelectronic properties of the film. To probe the kinetics of the transition, we combine an ex-situ analysis via polarized optical spectroscopy and atomic force microscopy with a photoluminescence investigation carried out in-situ, based on monitoring the efficiency of the singlet fission process typical of crystalline RUB. Building on the insights gained, we tune the thin film growth and post-growth parameters, so as to obtain centimeter-scale, highly homogeneous and crystalline RUB thin films, constituted by several μm-sized and coherently oriented domains, featuring oxidation resistance.

The ability to control the properties of organic thin films is crucial for obtaining highly performant thin-film devices. However, thin films may experience post-growth processes, even when the most sophisticated and controlled growth techniques such as organic molecular beam epitaxy (OMBE) are used. Such processes can modify the film structure and morphology and, thus, the film properties ultimately affecting device performances. For this reason, probing the occurrence of post-growth evolution is essential. Equally importantly, the processes responsible for this evolution should be addressed in view of finding a strategy to control and, possibly, leverage them for driving film properties. Here, nickel-tetraphenylporphyrin (NiTPP) thin films grown by OMBE on highly oriented pyrolytic graphite (HOPG) are selected as an exemplary system exhibiting a remarkable post-growth morphology evolution consistent with Ostwald-like ripening. To quantitatively describe the growth, the height-height correlation function (HHCF) analysis of the atomic force microscopy (AFM) images is carried out, clarifying the role of the post-growth evolution as an integral part of the whole growth process. The set of scaling exponents obtained confirms that the growth is mainly driven by diffusion combined with the presence of step-edge barriers, in agreement with the observed ripening phenomenon. Finally, the results together with the overall approach adopted demonstrate the reliability of the HHCF analysis in systems displaying post-growth evolution.

The present study reports on the synthesis of a new alkoxysilane-bearing light-responsive cinnamyl group and its application as a surface functionalization agent for the development of SiO₂ nanoparticles (NPs) with photoreversible tails. In detail, cinnamic acid (CINN) was activated with N-hydroxysuccinimide (NHS) to obtain the corresponding NHS-ester (CINN-NHS). Subsequently, the amine group of 3-aminopropyltriethoxysilane (APTES) was acylated with CINN-NHS leading to the generation of a novel organosilane, CINN-APTES, which was then exploited for decorating SiO₂ NPs. The covalent bond to the silica surface was confirmed by solid state NMR, whereas thermogravimetric analysis unveiled a functionalization degree much higher compared to that achieved by a conventional double-step post-grafting procedure. In light of these intriguing results, the strategy was successfully extended to naturally occurring sepiolite fibers, widely employed as fillers in technological applications. Finally, a preliminary proof of concept of the photoreversibility of the obtained SiO₂@CINN-APTES system has been carried out through UV diffuse reflectance. The overall outcomes prove the consistency and the versatility of the methodological protocol adopted, which appears promising for the design of hybrid NPs to be employed as building blocks for photoresponsive materials with the ability to change their molecular structure and subsequent properties when exposed to different light stimuli.

Acrylic colors are mixtures of several components that can be identified as pigments, binders, and fillers, so that, when analyzed, the characteristic response of the different components may not be recognizable. This limits the accuracy of spectroscopic techniques, nonetheless particularly useful as they are noninvasive and can be applied in situ on real artworks. Here, a method is proposed to chemically separate and identify the different components of acrylic colors, in order to be able to study their spectroscopic response separately, in particular by ultraviolet–visible–near-infrared diffuse reflectance. The results clearly show that the chemical and analytical method developed here is fully reliable, with the advantage of clearly separating the response of the different components without any change of their chromatic/chemical properties. As a case study, the new method is applied here to original acrylic colors used by the Italian artist Ico Parisi, in view of building a spectra database.

The nature of optical excitations and the spatial extent of excitons in organic semiconductors, both of which determine exciton diffusion and carrier mobilities, are key factors for the proper understanding and tuning of material performances. Using a combined experimental and theoretical approach, we investigate the excitonic properties of meso-tetraphenyl porphyrin-Zn(II) crystals. We find that several bands contribute to the optical absorption spectra, beyond the four main ones considered here as the analogue to the four frontier molecular orbitals of the Gouterman model commonly adopted for the isolated molecule. By using many-body perturbation theory in the GW and Bethe–Salpeter equation approach, we interpret the experimental large optical anisotropy as being due to the interplay between long- and short-range intermolecular interactions. In addition, both localized and delocalized excitons in the π-stacking direction are demonstrated to determine the optical response, in agreement with recent experimental observations reported for organic crystals with similar molecular packing.

Reflectance spectroscopy in the ultraviolet (UV), visible (Vis), and near infrared (NIR) range is widely applied to art studies for the characterization of paints and pigments, with the advantages of non-invasive techniques. Isolating and detecting the fingerprint of pigments, especially in the NIR range, is quite challenging, since the presence of vibrational transitions of the most common organic functional groups prevents to relate the optical spectrum of a composite sample, as an artwork is, to each one of its elements (i.e., support, binder, and specific pigment). In this work, a method is presented to obtain the UV-Vis-NIR optical response of the single components of a model composite sample reproducing an artwork, i.e., the support, the binder, and the pigment or dye, by using diffuse reflectance spectroscopy. This allowed us to obtain the NIR spectral fingerprint of blue pigments and to identify specific features possibly applicable for detecting cobalt and phthalocyanine blue colors in artwork analysis.