Water, a safe and benign solvent, contains low amounts of molecular oxygen, making it a solvent with high potential for a broad variety of photochemical reactions. Reaction containers such as micelles can allow for improved solubilities for a variety of organic molecules, thus allowing investigation of a broad set of substrates in water as solvent. Additionally, micelles have been shown to increase the triplet state lifetime of fluorophores due to decreased oxygen quenching . In this context, micelles have the potential to enable enhanced photochemical reactivity. Typically, photocatalysis has been employed to reach triplet state reactivity using visible light to avoid harmful UV irradiation. In this context, aggregates often show redshifted absorption when compared to their monomer counterparts. Interestingly, micelles have been shown to enhance aggregation induced emission (AIE) which can lead to phosphorescence at room temperature (RTP). Therefore, the formation of excited state aggregates and their use in photochemical synthesis represents an exciting strategy for visible light photochemistry. However, a drawback for this approach lies on the large size of the molecules usually exhibiting AIE, whereas photochemical synthesis is preferably carried out using small molecules. We envisioned that small molecules can form aggregates in micelles and in turn absorb visible light. The formed excited state aggregates can then promote a photochemical reaction. We selected the [2+2] photocycloaddition of chalcone as a model reaction to investigate the micelle mediated excited state aggregate formation and its potential for photochemical synthesis. The [2+2] photocycloaddition using chalcone has previously been investigated using direct excitation of chalcones with UV-light in organic solvents and CFL lamps under neat conditions. Additionally, energy transfer catalysis using for example Ir-based catalysts allows for the photocycloaddition to proceed under blue light irradiation. Several activation methods combined with lower triplet energy catalysts, or longer wavelength light have been used for reactions with chalcone derivatives. Herein, we explore chalcone (1a) as substrate for [2+2] photocycloadditions occurring through excited state aggregate formation and red shifted absorption. The concept allows for direct excitation with blue light, avoiding the need for the expensive Ir-based photocatalyst. Furthermore, the micellar medium influences excited-state properties and facilitates triplet state reactivity, thus allowing for an intermolecular [2+2] photocycloaddition not observed in organic solvents.