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Among the possible technologies for artificial photosynthesis, photoelectrochemical cells possess the advantage to decouple the overall water splitting reaction into the related semi-reactions enabling the study and optimization of the single process. In this Thesis a novel approach towards artificial photosystems design has been reported. The quantasome approach is a unique bio-inspired design strategy that pair down to essentials the PSII mimicry by shaping an innovative supramolecular material with the essential components of the quantasome: a light-harvesting antenna and a catalytic reaction center embedded in a unique ensemble. Bonchio, Prato and co-workers reported the very first example of an artificial quantasome (QS), a supramolecular artificial photosystem designed for light-induced water oxidation reaction. This innovative material is composed of a bis-cationic perylene bisimide photosensitizer (PBI2+) and a deca-anionic state-of-the-art water oxidation catalyst (Ru4POM). The artificial quantasome assembly forms in water, exploiting the complementary electrostatic interactions and hydrophobic-hydrophilic properties of the two selected molecular building blocks resulting in a supramolecular material (QS) with a definite chromophore to catalyst stoichiometry of 5:1. The structural characterization of this artificial quantasome (QS) and its building blocks, using state-of-the-art techniques of scanning probe microscopy and electron microscopy, is reported. The experiments performed point out to a lamellar structure of the supramolecular material resembling the self-organization of the natural enzyme PSII. This project aimed also at the synthesis of new artificial photosystems, indeed innovative hydrophilic photosynthetic materials are obtained by a combined supramolecular and click-chemistry strategy. The designed synthetic procedure adopted relies on click-chemistry functionalization of the N-terminal positions of PBI scaffolds. The functionalization of the N-terminal positions of a PBI scaffold set the parallelism with the natural antennae, that via N-terminal loops interactions modulate the structure of PSII-LHCII supercomplexes. Both new chromophores PBIn-TEGlock and PBI-TEGunlock present and estimated potential of the excited state suitable to drive photo-assisted water oxidation. Moreover, the synthetic route here reported is envisaged to maintain the positive peripherical charges on the molecular structures obtained in order to exploit complementary electrostatic interaction with Ru4POM water oxidation catalyst (WOC). The interactions of these new antennae with Ru4POM WOC yield unprecedented artificial quantasomes (QS-TEGlock, QS-TEGunlock) with tetraethylene glycol (TEG) functionalization. Photoelectrocatalytic characterization of the new artificial quantasomes is reported by coupling the supramolecular materials with state-of-the-art “inverse opal” indium tin oxide (IO-ITO) substrates. IO architectures are selected because their structure is reported to promote internal light scattering, due to the intrinsic geometry of the 3D-photoconductive lattice. QS-TEGlock exhibits a superior response for all the conditions explored, reporting a 340% photocurrent enhancement with respect to QS. In order to decouple the hydrophilic effect of TEG terminals from their cross-linking impact photoelectrocatalytic characterization of QS-TEGunlock is achieved. It is found that the decoration of the PBI chromophores with TEG residues, with or without cross-linking, can leverage the quantasome hydration and facilitate water oxidation reaction. Formation of TEG-templated hydration shells is verified by Raman microscopy of water exposed photoanodes.11 The presence of TEG-templated hydration shells sets a parallelism with natural PSII water channels. The added value of TEG cross-linkers is probed under prolonged photoelectrolysis whereby the unlocked structure reports a major photocurrent loss with respect to the locked one. Among the possible technologies for artificial photosynthesis, photoelectrochemical cells possess the advantage to decouple the overall water splitting reaction into the related semi-reactions enabling the study and optimization of the single process. In this Thesis a novel approach towards artificial photosystems design has been reported. The quantasome approach is a unique bio-inspired design strategy that pair down to essentials the PSII mimicry by shaping an innovative supramolecular material with the essential components of the quantasome: a light-harvesting antenna and a catalytic reaction center embedded in a unique ensemble. Bonchio, Prato and co-workers reported the very first example of an artificial quantasome (QS), a supramolecular artificial photosystem designed for light-induced water oxidation reaction. This innovative material is composed of a bis-cationic perylene bisimide photosensitizer (PBI2+) and a deca-anionic state-of-the-art water oxidation catalyst (Ru4POM). The artificial quantasome assembly forms in water, exploiting the complementary electrostatic interactions and hydrophobic-hydrophilic properties of the two selected molecular building blocks resulting in a supramolecular material (QS) with a definite chromophore to catalyst stoichiometry of 5:1. The structural characterization of this artificial quantasome (QS) and its building blocks, using state-of-the-art techniques of scanning probe microscopy and electron microscopy, is reported. The experiments performed point out to a lamellar structure of the supramolecular material resembling the self-organization of the natural enzyme PSII. This project aimed also at the synthesis of new artificial photosystems, indeed innovative hydrophilic photosynthetic materials are obtained by a combined supramolecular and click-chemistry strategy. The designed synthetic procedure adopted relies on click-chemistry functionalization of the N-terminal positions of PBI scaffolds. The functionalization of the N-terminal positions of a PBI scaffold set the parallelism with the natural antennae, that via N-terminal loops interactions modulate the structure of PSII-LHCII supercomplexes. Both new chromophores PBIn-TEGlock and PBI-TEGunlock present and estimated potential of the excited state suitable to drive photo-assisted water oxidation. Moreover, the synthetic route here reported is envisaged to maintain the positive peripherical charges on the molecular structures obtained in order to exploit complementary electrostatic interaction with Ru4POM water oxidation catalyst (WOC). The interactions of these new antennae with Ru4POM WOC yield unprecedented artificial quantasomes (QS-TEGlock, QS-TEGunlock) with tetraethylene glycol (TEG) functionalization. Photoelectrocatalytic characterization of the new artificial quantasomes is reported by coupling the supramolecular materials with state-of-the-art “inverse opal” indium tin oxide (IO-ITO) substrates. IO architectures are selected because their structure is reported to promote internal light scattering, due to the intrinsic geometry of the 3D-photoconductive lattice. QS-TEGlock exhibits a superior response for all the conditions explored, reporting a 340% photocurrent enhancement with respect to QS. In order to decouple the hydrophilic effect of TEG terminals from their cross-linking impact photoelectrocatalytic characterization of QS-TEGunlock is achieved. It is found that the decoration of the PBI chromophores with TEG residues, with or without cross-linking, can leverage the quantasome hydration and facilitate water oxidation reaction. Formation of TEG-templated hydration shells is verified by Raman microscopy of water exposed photoanodes.11 The presence of TEG-templated hydration shells sets a parallelism with natural PSII water channels. The added value of TEG cross-linkers is probed under prolonged photoelectrolysis whereby the unlocked structure reports a major photocurrent loss with respect to the locked one. |
