Controlled Aggregation of Pyrene‐Based Supramolecular Nanostructures for Light‐Driven Switchable H ₂ or H ₂ O ₂ Production

Abstract Self‐assembled organic chromophores form nanostructures in solutions, with their molecular packing determining the optoelectronic properties and photocatalytic activity. Here an organic dye molecule is reported, 1,3,6,8‐tetrakis(4‐ethynylbenzoic acid)pyrene (TEBAPy), that exhibits two aggregate states in aqueous conditions: nanofibers or nanoparticles, depending on the charge‐screening conditions. The nanofibers promote sacrificial photocatalytic hydrogen production (H ₂ , 84 mmol g ⁻¹ h ⁻¹ ) while the nanoparticles produce hydrogen peroxide (H ₂ O ₂ , 85 mmol g ⁻¹ h ⁻¹ ). Using a combination of structural and photophysical characterizations, it is shown that the photocatalytic activity is determined by the nature of the formed self‐assembled aggregate, demonstrating the potential of supramolecular nanostructures to tune their activity and switch their reactivity. It is shown clear correlation between the presence of fibrous nanostructures and photocatalytic H ₂ evolution, with spectroscopy showing mixing of excitonic states that enables efficient charge separation over multiple chromophore units. In the nanoparticular aggregates, on the contrary, the excitation is localized and leads to excimer formation that is involved in H ₂ O ₂ production. The results demonstrate that the molecular packing of a single chromophore in self‐assembled organic nanostructures can not only optimize solar fuel production but also enable multiple and switchable photocatalytic functions.