Rylene Diimide-Based Systems as Supramolecular Organic Semiconductors in Water

The development of functional, water-compatible organic semiconductors demands precise control over the supramolecular organization of chromophoric building blocks in aqueous media. This Master's Thesis addresses this challenge at the intersection of supramolecular chemistry, organic electronics, and solar energy conversion. The research is grounded in a bottom-up supramolecular strategy, exploiting the structural and optoelectronic features of two classes of rylene diimide chromophores: (i) perylene bisimides (PBIs) and pyromellitic diimides (PmDIs) as molecular building blocks for the construction of functional self-assembled systems. Both families share key photophysical attributes, including high molar extinction coefficients, high fluorescence quantum yield, strong π-stacking interactions (H- or J-type aggregates), and synthetic versatility. The work is structured along two lines of investigation, addressing structure–assembly relationships. The first line focuses on PmDI-based chromophores. Compared to PBIs, their HOMO-LUMO energy gap makes the triplet excited state (T₁) more thermally and photophysically accessible, with implications for photosensitization, photocatalysis, and the generation of reactive oxygen species. Motivated by these features, the aggregation behaviour of structurally diversified PmDI derivatives was systematically investigated through a multi-technique approach combining UV-Vis absorption spectroscopy, steady-state fluorescence spectroscopy, single crystal X-ray diffraction (SCXRD) and EPR spectroscopy. The Thesis work provides the first experimental evidence of J-type aggregation behaviour in pyromellitic diimide-based supramolecular systems. These findings establish a preliminary framework for the rational engineering of PmDI-based supramolecular semiconductors with tunable excited-state properties. The findings presented in this Thesis build on molecular substitution as a powerful handle for programming supramolecular self-assembly that control the optoelectronic properties of chromophore aggregates in aqueous solutions for the future development of artificial photosynthetic assemblies, OMIEC-based bioelectronic devices, and metal-free photocatalytic systems for sustainable solar energy conversion. The second line focuses on Ion-Responsive PBI-Based structures, exploiting ion–crown ether coordination as a tunable driver for the PBI supramolecular polymerization. Such architectures, capable of sustaining both electronic and ionic conduction can behave as organic mixed ionic-electronic conductors (OMIECs), a key material platform for bioelectronics and energy research. PBI derivatives incorporating 15-crown-5-ether, have been synthesized. The synthetic strategy was optimized through a stepwise approach, enabling the successful isolation and full characterization of the final key synthetic intermediate, validating the overall design. These results open new perspectives toward ion-gated aggregation and pH-responsive modulation of optoelectronic properties.