Abstract
Supramolecular photochemistry uses molecular encapsulation to control excited-state reactions with exceptional precision. Confinement within host cavities tunes reaction pathways, stabilizes reactive intermediates, and suppresses competing processes—enabling outcomes often inaccessible in bulk solution. This work explores the water-soluble host Octa Acid (OA) capsule as a nanoscale reactor that imposes structural and dynamical constraints on guests, directing their photochemistry. In water, β-ionyl derivatives above ~0.5–1 mM form nano-aggregates, competing with host binding. OA encapsulation overcomes this self-assembly and enables unique reactivity. The high-energy 7-cis-β-ionone is stabilized in OA, reaching ~40% yield after UV irradiation compared to ~10% in bulk, as confinement suppresses cyclization. Visible-light E→Z isomerization of β-ionyl derivatives becomes regioselective in OA, selectively targeting one alkene and stabilizing higher-energy Z-isomers. Unexpected triplet energy transfer between OA and anionic sensitizers reveals “like-charge attraction” effects in water. The OA capsule accelerates the “catalysis-resistant” dimerization of cyclopentadiene by >2000-fold via guest pre-organization and sequential turnover, demonstrating confinement-driven catalysis. For arylazoisoxazole molecular switches, OA encapsulation restricts mobility but maintains reversible E/Z isomerization. CH–π interactions and substituents shift photostationary equilibria and thermal reversion rates, tuning switching performance over many cycles without host dissociation. Overall, OA enables stabilization of fleeting species, precise control of selectivity, unexpected energy-transfer pathways, dramatic rate enhancements, and modulation of photoswitch behavior. These findings establish supramolecular encapsulation in water as a powerful strategy for designing precision photochemical systems and expand the conceptual toolkit for controlling light-driven processes in aqueous environments.