Photochemistry of Sulfur-Substituted Small Molecules Encapsulated Within a Water-Soluble Host

Abstract

Supramolecular chemistry is widely employed by nature to direct and control highly precise chemical transformations, most notably in enzyme&ndash;substrate systems, where noncovalent interactions provide both selectivity and rate enhancement. Inspired by these biological systems, we utilized the water-soluble supramolecular host octa-acid (OA) to investigate photochemical reactions under confined aqueous conditions.In this dissertation, we demonstrate that encapsulation within OA creates a unique microenvironment that alters reactivity, stabilizes reactive intermediates, and modulates reaction pathways. We first investigated the photochemistry of dispiro-substituted diketones and found that confinement within OA in borate buffer leads to the generation and remarkable stabilization of ketene intermediates, significantly extending their lifetimes relative to bulk water. We further examined strained thioxo derivatives and observed the formation of distinct photoproducts in the presence of OA, underscoring the profound influence of host&ndash;guest interactions and spatial confinement on photochemical outcomes. Additionally, we studied a 7-methoxythiocoumarin-based phototrigger, which is inherently hydrophobic. Encapsulation within OA enabled its solubilization in water and facilitated the photorelease of acidic products. Confinement promoted formation of a radical anion&ndash;type intermediate via a triplet-state pathway, providing new mechanistic insight into photochemical processes operating under confined conditions.Finally, a comparative mechanistic investigation of substitution effects in coumarin triggers at 2-position (oxygen versus sulfur) and the 7-position (methyl-substituted versus unsubstituted) revealed that subtle structural modifications critically govern excited-state behavior, intermediate formation, and overall reaction mechanisms within the supramolecular cavity.&nbsp;</p