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Light‐ and pH‐regulated Water‐soluble Pseudorotaxanes Comprising a Cucurbit[7]uril and a Flavylium‐based Axle
Author(s) -
Seco André,
Yu Shilin,
Tron Arnaud,
McClenaghan Nathan D.,
Pina Fernando,
Jorge Parola A.,
Basílio Nuno
Publication year - 2021
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.202102343
Subject(s) - moiety , cucurbituril , chemistry , chalcone , fluorescence , photoisomerization , photochemistry , pyridinium , quantum yield , stereochemistry , crystallography , medicinal chemistry , supramolecular chemistry , organic chemistry , crystal structure , physics , quantum mechanics , isomerization , catalysis
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.