Excimers, excited‐state dimers formed through short‐range interactions between identical chromophores, exhibit unique photophysical properties that are highly sensitive to molecular proximity and geometry. While excimer emission has been extensively exploited as a spectroscopic probe, its potential as a reactive excited‐state intermediate in photochemical synthesis has received comparatively less attention, particularly in aqueous media. This review surveys host‐mediated excimer formation in water, emphasizing how supramolecular confinement within cyclodextrins, cucurbiturils, micelles, and related assemblies enables excimer generation with aromatic guests. Host–guest complexation enhances solubility, local concentrations, and orientational control. Excimers can be stabilized compared to their excited state monomer counter‐parts and in addition, competing non‐radiative decay pathways can be suppressed. These features have the potential to be translated into improved efficiency, regioselectivity, and stereoselectivity in photochemical transformations such as 2 + 2 and 4 + 4 photocycloadditions, photodimerizations, and other excimer‐mediated reactions that are otherwise inaccessible in bulk solutions. By describing excimer formations across diverse host systems, this review highlights the potential of excimer formation under confinement to be used as a design principle for photochemical synthesis in water. The promise of supramolecular excimers as a strategy towards sustainable, oxygen‐tolerant, and selective photochemical reactions is thereby outlined.
Akbulut et al. (Wed,) studied this question.