Light‐ and pH‐regulated Water‐soluble Pseudorotaxanes Comprising a Cucurbit[7]uril and a Flavylium‐based Axle. Issue 66 (21st October 2021)

• Record Type: Journal Article
• Authors: Seco, André; Yu, Shilin; Tron, Arnaud; McClenaghan, Nathan D.; Pina, Fernando; Jorge Parola, A.; Basílio, Nuno
• Is Part Of: Chemistry. Volume 27:Issue 66(2021)
• Page Start: 16512
• Page End: 16522
• Publication Date: 2021-10-21
• Subjects: Chalcones -- flavylium -- photochemistry -- rotaxanes -- supramolecular chemistry; Chemistry -- Periodicals; 540
• DOI: 10.1002/chem.202102343
• Languages: English
• ISSNs: 0947-6539

Abstract

Abstract: A linear double pyridinium‐terminated thread comprising a central chalcone moiety is shown to provide two independent binding sites with similar affinity for cucurbit[7]uril (CB7) macrocycles in water as judged from NMR, UV‐Visible and fluorescence spectroscopies. Association results in [2] and [3]pseudorotaxanes, which are both pH and photosensitive. Switching from the neutral chalcone to the cationic flavylium form upon irradiation at 365 nm under acidic conditions provided an enhanced CB7 association ( K 1:1 increases from 1.2×10 5 M −1 to 1.5×10 8 M −1 ), limiting spontaneous on‐thread cucurbituril shuttling. This co‐conformational change in the [2]pseudorotaxane is reversible in the dark with k obs =4.1×10 −4 s −1 . Threading the flavylium moiety into CB7 leads to a dramatic increase in the fluorescence quantum yield, from 0.29 in the free axle to 0.97 in the [2]pseudorotaxane and 1.0 in the [3]pseudorotaxane. Abstract : A linear double pyridinium‐terminated thread comprising a central trans ‐chalcone moiety forms pseudorotaxanes with cucurbit[7]uril (CB7), in water. Irradiation of the chalcone under slightly acidic conditions triggers the formation of the fluorescent cationic flavylium form with displacement of the CB7 ring along the thread, defining a pH‐dependent photoswitch for ring translocation with fluorescence read‐out. The system returns to the initial trans ‐chalcone state in the dark through a series of consecutive reversible reactions characteristic of flavylium‐based molecular switches.