Controlling Perylene Bisimide Aggregation in Aqueous Media: Stable J-Aggregates and Wireless Heterogeneous Quantasomes

The design and control of supramolecular architectures based on perylene bisimides (PBIs) has emerged as a powerful strategy to engineer functional light-harvesting and catalytic assemblies. The rigid π-conjugated perylene core, together with versatile imide and bay substitution patterns, endows PBIs with exceptional photostability, strong absorption in the visible region and tunable aggregation. These features make PBIs uniquely suited as building blocks for artificial photosynthesis and excitonic devices. Despite extensive progress in organic media, mastering PBI self-assembly in water, which is a highly competitive yet essential solvent for biological and catalytic applications, remains a central challenge in supramolecular chemistry. In this thesis, PBI supramolecular aggregation is investigated with a particular focus on aqueous media, addressing both the fundamental principles of self-assembly and their translation into photocatalytic function. The first part centers on the rational design and synthesis of a pyridyl-substituted perylene bisimide (4Py-PBI), tailored to favour tail-to-tail (J-type) aggregation through the synergy of hydrogen bonding and π–π stacking. Computational and spectroscopic analyses revealed that in water, 4Py-PBI undergoes a robust directional self-assembly, yielding extended J-aggregates with distinct red-shifted absorption bands and highly ordered multi-strand layers observed by HR-TEM. Water compatibility was achieved through a fine balance between hydrophobic collapse and a protonation/deprotonation “dance” of pyridine units, thus overcoming the long-standing limitation of poor aggregate control in aqueous media. Moreover, a chiral induction study demonstrated a significant transfer of optical activity from the chiral dopant, accompanied by a structural transition in HR-TEM from linear multi-strands to spiral aggregates. These results not only provide a blueprint for directing PBI aggregation in water but also underscore the role of supramolecular design in tuning optical and electronic properties. The second part of the thesis addresses a different set of challenges. Building on the “quantasome hypothesis,” which defines the minimal functional unit for light-driven reactions in photosynthesis, this work explores a novel artificial quantasome (QS) platform. The first-generation [PBI]₅RuPOM assemblies reported by Bonchio and co-workers in 2019 consisted of water-soluble cationic PBIs encapsulating a RuPOM water oxidation catalyst, self-organizing into supramolecular lamellae. To overcome the precipitation issues of these assemblies in aqueous medium, a new strategy was developed in collaboration with CICbiomaGUNE. Agarose beads were employed as soft, hydrophilic supports to host the co-assembly of PBIs, RuPOM, and the biological redox mediator Cytochrome C. This heterogeneous platform integrates all the key components of the original QS architecture, offering a modular system that mimics the cooperative interplay of pigments and cofactors in natural photosystems. While performance testing remains the subject of future studies, the successful establishment of a stable bead-supported architecture represents a crucial step toward wireless photocatalytic systems for sustainable artificial photosynthesis. Altogether, this thesis establishes a coherent trajectory from molecular design to functional application: beginning with the creation of a novel PBI scaffold for stable aqueous J-aggregation and extending to the development of heterogeneous supramolecular photocatalysts. By elucidating the interplay between π–π stacking, hydrogen bonding, and hydrophobic effects, this work provides new tools for the design of supramolecular architectures, broadly relevant to molecular materials science, light-harvesting processes, and artificial photosynthesis.