Mocerino, Fabio (2024) Synthesis and study of nature-inspired polymers for applications in organic electronics. [Tesi di dottorato]

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Abstract

Natural polymers have attracted great interest as functional materials in the field of organic electronics for innovative technological and biomedical applications. In the panorama of biomaterials, melanins are undoubtedly among the most intriguing natural substances. The most studied and abundant class of melanins is eumelanin, a mammalian photoprotective pigment originating from the oxidative polymerization of 5,6-dihydroxy indole (DHI) and 5,6-dihydroxyindole-2 carboxylic acid (DHICA). In this context the main objectives of the present project can be summarized as follows: a) preparation of eumelanin-inspired materials through a strategy based on a synthetic approach; b) carry forward the process of elucidation of the structure of eumelanin through the comparison of the synthesis mechanism of melanin derivatives with that of the natural polymer starting from DHI and DHICA. c) preparation and characterization of a eumelanin-inspired material for its potential application as an active layer for organic electronics devices with improved performance compared to natural polymer. Regarding the results obtained, a synthetic procedure was found to functionalize the eumelanin precursor DHICA by introducing a benzothiazole synthon. Investigations of the optical properties of the acetylated derivative of the adduct, DAICA-ABtz, revealed specific chelation capabilities towards Zn2+ ions along with a notable increase in fluorescence intensity. Early studies addressed the chemistry of oxidative polymerization of DHICA-ABtz focusing on the isolation of oligomeric intermediates to gain insight into the structure of the resulting polymer. The feature pattern of C–C bonds identified in the DHICA-ABtz dimers concluded that the benzothiazole system did not influence the regioselectivity of the polymerization in the early stages of the process. Subsequent research activities focused on the potential application of the DHICA-ABtz-derived polymer as a solid active layer in electrochemical energy storage 5 devices, exploiting the specific ability of the eumelanin-inspired material to chelate Zn2+ ions as well as the intrinsic redox behaviour of eumelanin. The ionic conductivity values found by studying DHICA-ABtz-derived polymer films with different amounts of zinc were modest compared to the values of current solid polymer electrolytes. Interestingly, the electrochemical characterization of the solid melanin-inspired polymer immersed in an aqueous electrolyte containing zinc ions highlighted a remarkable specific capacity, almost two times greater than that of the DHICA eumelanin. This result is crucial for the development of an active layer for electrochemical energy storage devices, although further analyses are needed in this perspective.

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