Cyclodextrin-Based [c2]Daisy Chain Rotaxane Insulating Two Diarylacetylene Cores

A [c2]daisy chain rotaxane with two diarylacetylene cores was efficiently synthesized in 53 % yield by capping a C-2-symmetric pseudo[2]rotaxane composed of two diarylacetylene-substituted permethylated alpha-cyclodextrins (PM alpha-CDs) with aniline stoppers. The maximum absorption wavelength of the [c2]daisy chain rotaxane remained almost unchanged in various solvents, unlike that of the stoppered monomer, indicating that the two independent diarylacetylene cores were insulated from the external environment by the PM alpha-CDs. Furthermore, the [c2]daisy chain rotaxane exhibited fluorescence emission derived from both diarylacetylene monomers and the excimer, which implies that the [c2]daisy chain structure can undergo contraction and extension. This is the first demonstration of a system in which excimer formation between two pi-conjugated molecules within an isolated space can be controlled by the unique motion of a [c2]daisy chain rotaxane.

Automated summary

In this study, a [c2]daisy chain rotaxane with two diarylacetylene cores was efficiently synthesized, demonstrating that the two independent cores were insulated by permethylated alpha-cyclodextrins. The rotaxane showed stable absorption wavelengths in different solvents and exhibited fluorescence emission from both diarylacetylene monomers and the excimer, suggesting the ability for contraction and extension. This is the first example showing that excimer formation between two pi-conjugated molecules within an isolated space can be controlled by the unique motion of a [c2]daisy chain rotaxane.