Post-Functionalization of Rotaxane-Type Cyanine Dyes via Cross-Coupling Reactions

Abstract

A novel rotaxane-type cyanine dye bearing reactive iodine substituents was developed as a versatile platform for post-synthetic functionalization. The dye was synthesized from an α-cyclodextrin-encapsulated cyanine scaffold followed by host permethylation, which enhanced both lipophilicity and structural stability, thereby enabling efficient cross-coupling reactions in organic media. Owing to the combination of the highly reactive iodine substituents and the stabilized permethylated cyclodextrin-encapsulated structure, diverse functional groups were successfully introduced through the Suzuki, Heck, Sonogashira, and Stille cross-coupling reactions under relatively mild conditions. This synthetic versatility enabled the efficient preparation of both monomeric and polymeric functional dyes with tunable photophysical and electronic properties tailored for specific applications. Importantly, encapsulation of the polymethine backbone by permethylated cyclodextrin effectively suppressed photodegradation under irradiation and oxidative conditions, resulting in dramatically improved photostability. These results demonstrate that rotaxane-based encapsulation combined with post-functionalization provides a powerful and flexible molecular platform for the development of stable and application-oriented near-infrared cyanine materials.