Light‐ and pH‐regulated Water‐soluble Pseudorotaxanes Comprising a Cucurbit[7]uril and a Flavylium‐based Axle.

Seco, André; Yu, Shilin; Tron, Arnaud; McClenaghan, Nathan D.; Pina, Fernando; Jorge Parola, A.; Basílio, Nuno

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 (K1:1 increases from 1.2×105 M−1 to 1.5×108 M−1), limiting spontaneous on‐thread cucurbituril shuttling. This co‐conformational change in the [2]pseudorotaxane is reversible in the dark with kobs=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.

CUCURBITACEAE; FLUORESCENCE yield; BINDING sites; ULTRAVIOLET-visible spectroscopy; CHALCONE; FLUORESCENCE spectroscopy

Chemistry - A European Journal, 2021, Vol 27, Issue 66, p16512

0947-6539

Academic Journal

10.1002/chem.202102343