Squaraine rotaxane shuttle as a ratiometric deep-red optical chloride sensor

Abstract

A new squaraine rotaxane molecular shuttle exhibits high chemical stability and acts as a deep-red, fluorescent and colorimetric sensor for Cl À anion with reversible, ratiometric response. The molecular design encapsulates a dihydroxyl substituted squaraine dye inside an anthracene-containing tetralactam macrocycle and a "clicked capping" reaction was used to convert an appropriate pseudorotaxane precursor into a permanently interlocked rotaxane in high yield. Reversible binding of Cl À to the rotaxane in solution, or on the surface of prototype dipsticks, causes lateral displacement of the surrounding macrocycle away from the central squaraine station and a substantial 30-40 nm shift in the squaraine absorption/fluorescence maxima that can be easily detected by the naked eye. The collective attributes of intense absorption/emission and ratiometric response at deep-red wavelengths is a significant advance in optical Cl À sensor performance by an organic molecule.

Anion Receptor Chemistry

“…A ratiometric Cl À sensor, 101 ( Figure 34A), was recently developed by Collins et al 53 on the basis of a squaraine rotaxane scaffold. In 101, the tetralactam macrocycle binds to the center of the squaraine anion via four amide NH hydrogen-bond donors, causing a red-shift of squaraine fluorescence that was attributed to squaraine rigidification as a result of encapsulation.…”

The Supramolecular Chemistry of Strained Carbon Nanohoops

“…However, the lack of heteroatoms and the relatively large ring sizes of the prototypical nanohoops featured in this Minireview pose unique challenges that neither Sauvage's classic metal template strategy nor Leigh's active metal template synthesis are suited to address. We believe it is worthwhile taking up this challenge, because MIAs are increasingly finding applications, from molecular machinery to sensing and catalysis, and because π‐conjugated nanohoops have unique properties to offer when compared with most other macrocycles.…”

Halogen bonding in water results in enhanced anion recognition in acyclic and rotaxane hosts

“…Interlocked molecules (in which two or more molecules are mechanically interlocked but not covalently linked) such as rotaxanes and catenanes have been reported to be effective anion receptors, utilizing the unique three-dimensional binding cavity formed between the interlocked components to encapsulate the anion 31,32 . To date, however, anion recognition in pure water by such interlocked molecules has been thwarted by a lack of aqueous solubility of such receptors 33 .…”