Photoluminescent materials: from organic molecules to nanomaterials

The research has been focused on tailoring novel photosensitizers, ranging from organic molecules to carbon nanostructure, such as perylene bisimides (PBIs) and carbon nanodots (CNDs): At first it was developed a fast and efficient protocol for the microwave assisted synthesis of perylene bisimides. Imidation reactions of the perylenebisanhydride were performed using a large variety of amines, such as alkylamines, amino alcohols, heteroarylamines, and amino acids. With the powerful tool we developed, we targeted more complex applications. We designed a novel photocatalytic system mimicking the PSII oxygen evolving center. Our approach was based on the unprecedented combination of metal-free perylene bisimides (PBI) as photosensitizers with totally inorganic polyoxometalates (POMs) as catalysts. Oxygen evolution was observed with well-behaved kinetics, long operation time (> 8h), and conversion yields up to >98%. Moreover, we proposed comprehensive structural picture of a perylenebisimide hydrogel, suggesting that its long-range conductivity is limited by charge-transfer between electronic backbones. We revealed nano-crystalline ribbons as the electronic and structural backbone between which charge transfer was mediated by polar solvent bridges. We exemplified this effect with gas sensing, where exposure to polar vapor changes conductivity by five orders of magnitude, emphasizing the crucial role of the interplay between structural motif and surrounding medium for the rational design of devices based on nano-crystalline hydrogels. Jumping to carbon nanostructure we were interested into mastering optical, electronical and structural properties of carbon dots. Thus, we synthesized and characterized green emissive CNDs using organic chromophores, such as boron-dipyrromethenes, as starting materials and we exploited them as tracker in NK cells. Notably, it was optimized a synthetic protocol for the green emissive CNDs that can be extended for the preparation of a library of multicolored CNDs. Furthermore, we prepared and characterized a redox library of CNDs with tunable energy levels by adding to the reaction mixture commercially available quinones and employing a bottom-up MW-assisted hydrothermal treatment. Benzoquinone-, naphthoquinone- and anthraquinone-based carbon nanodots exhibited interesting electrochemistry with oxidation potentials between 1..48 V and 0.98 V vs SCE and reducing one in the range -1.52 V and -2.05 V vs SCE. Finally, we reported the structural and optical modifications happening during the reaction. We identified the core-shell structure of these carbon dots and synthesized novel CNDs with controlling the size of the soft shell that we believe it is the responsible for the optical properties that characterize these interesting nanoparticles.