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Cavity-confined Luminophores for Advanced Photonic Materials: A Training Action for Young Researchers

Final Report Summary - FINELUMEN (Cavity-confined Luminophores for Advanced Photonic Materials: A Training Action for Young Researchers)

FINELUMEN primarily targeted new luminescent materials in which organic or inorganic luminophores are encapsulated in carbon nanotubes (CNTs) and organic cavitands. The objective of this strategy is twofold: to preserve/improve the emission output of the guest thanks to chemical and physical protection and to provide the luminophores with the peculiar physical properties (e.g. electronic, mechanical) of the host. The project produced several tens of scientific papers in highly ranked journals and 2 invention disclosures, with wide-ranging technical implications. The consortium has developed new organic and inorganic emitters with high luminescence efficiency, particularly Cu(I) complexes that are extremely appealing as replacements of materials based on rare and costly metals of the platinum group. Several protocols for the preparation, oxidation, tip opening, and functionalization of CNT were optimized. A milestone result of the project is the establishment of a protocol for the insertion of a suitably selected neutral and hydrophobic complex of Eu(III) in the interior of multiwalled carbon nanotubes (MWCNTs). This unprecedented material, extensively characterized with state-of-the-art spectroscopic and microscopic techniques, largely retains the emission properties of the red-emitting luminophores and may open the route to a brand new type of organic/inorganic carbon-based luminophores. Along this line we have also validated a low-temperature methodology to fill single- and multiwalled carbon nanotubes with various organic chromophores and luminophores using supercritical carbon dioxide. Over the years we have also developed strategies to make CNTs easier to handle, disperse, and functionalize. To this end we have developed and standardized methods based on weak interactions that entail the formation of supramolecular copolymers that wrap around the carbon nanostructure via p-stacking and prompt extensive debundling. This approach was further extended to the use of photothermally responsive supramolecular polymers containing azobenzene units, which can trigger precipitation of CNT via light irradiation. Notably, also external functionalization of CNT with a suitably designed anionic Eu(III) complex has been accomplished via electrostatic interactions, opening the route to highly soluble and luminescent carbon nanotube materials. On the other hand, also carbon nanohorns (CNH) and fullerenes were functionalized to get novel luminescent and/or photoactive materials featuring charge separation. As far as the latter topic is concerned, double-walled CNTs have been tested in connection with porphyrins to make photoactive electron donor-acceptor materials for photovoltaic devices. Other key host structures investigated by FINELUMEN are cavitands based on tetraphosphonates which are excellent hosts for luminophores (Ln(III) complexes) and can be anchored to silicon surfaces. On the other hand, quinoxaline-based cavitands have been demonstrated to be excellent luminescent receptors for aromatic hydrocarbons.
Our project went beyond the initially stated targets and addressed not only the encapsulation of luminescent materials but also of magnetically active guests. In fact novel magnetic MWCNTs were prepared by filling their inner cavities with Fe(II) particles, which were further functionalized with an antibody that promotes binding to cancer cells selectively. The magnetic properties of the CNT scaffolds facilitate the separation of cancer cells from normal cells with remarkable applicative potential in cancer therapy. Additionally, arrays of aligned CNTs have been grown on surfaces by advanced physical techniques for manufacturing field emissive X-ray cathodes.
The relevant progress made in several fields of knowledge by FINELUMEN, as briefly summarized above, can be expolited in various applicative fields related to materials science, optoelectronic devices for lighting or solar energy conversion, photoactive liquid crystals, diagnostics, therapy, and environmental monitoring. Some of these possibilities have been demonstrated by the consortium as proof-of-principles.
Over 20 young researchers were trained by the FINELUMEN consortium through advanced research in the area of chemistry, physics, engineering, and biology. They have now gained a multidisciplinary background in several disciplines and had the infrequent opportunity to interact with both the academic and industrial sectors, also acquiring a wider portfolio of soft and transferable skills, e.g. in management, communication, intellectual property rights. The fruitful training experience matured within FINELUMEN makes them privileged candidates to get leading positions, both in academia and industry, in several fields of materials science, including preparation, characterization, technological implementation, and marketing.