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

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

doi:10.1002/chem.202102343

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

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

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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 1.2×10⁵ 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 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.

Original language	English
Pages (from-to)	16512-16522
Journal	Chemistry - A European Journal
Volume	27
Issue number	66
DOIs	https://doi.org/10.1002/chem.202102343
Publication status	Published - 25 Nov 2021

Keywords

Chalcones
flavylium
photochemistry
rotaxanes
supramolecular chemistry

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@article{d4476be0908e4420b9e800e40cd83e01,

title = "Light- and pH-regulated Water-soluble Pseudorotaxanes Comprising a Cucurbit[7]uril and a Flavylium-based Axle",

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 (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.",

keywords = "Chalcones, flavylium, photochemistry, rotaxanes, supramolecular chemistry",

author = "Andr{\'e} Seco and Shilin Yu and Arnaud Tron and McClenaghan, {Nathan D.} and Fernando Pina and {Jorge Parola}, A. and Nuno Bas{\'i}lio",

note = "Funding Information: This work was supported by the Associate Laboratory for Green Chemistry‐LAQV which is financed by national funds from FCT/MCTES (UIDB/50006/2020). FCT/MCTES is also acknowledged for supporting the National Portuguese NMR Network (ROTEIRO/0031/2013‐PINFRA/22161/2016, cofinanced by FEDER through COMPETE 2020, POCI, PORL, and FCT through PIDDAC) and for grants PTDC/QUI‐QFI/30951/2017 and 2020.07313.BD (A.S.). China Scholarship Council (S.Y.) is acknowledged. ",

year = "2021",

month = nov,

day = "25",

doi = "10.1002/chem.202102343",

language = "English",

volume = "27",

pages = "16512--16522",

journal = "Chemistry - A European Journal",

issn = "0947-6539",

publisher = "Wiley",

number = "66",

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TY - JOUR

T1 - Light- and pH-regulated Water-soluble Pseudorotaxanes Comprising a Cucurbit[7]uril and a Flavylium-based Axle

AU - Seco, André

AU - Yu, Shilin

AU - Tron, Arnaud

AU - McClenaghan, Nathan D.

AU - Pina, Fernando

AU - Jorge Parola, A.

AU - Basílio, Nuno

N1 - Funding Information: This work was supported by the Associate Laboratory for Green Chemistry‐LAQV which is financed by national funds from FCT/MCTES (UIDB/50006/2020). FCT/MCTES is also acknowledged for supporting the National Portuguese NMR Network (ROTEIRO/0031/2013‐PINFRA/22161/2016, cofinanced by FEDER through COMPETE 2020, POCI, PORL, and FCT through PIDDAC) and for grants PTDC/QUI‐QFI/30951/2017 and 2020.07313.BD (A.S.). China Scholarship Council (S.Y.) is acknowledged.

PY - 2021/11/25

Y1 - 2021/11/25

N2 - 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.

AB - 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.

KW - Chalcones

KW - flavylium

KW - photochemistry

KW - rotaxanes

KW - supramolecular chemistry

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U2 - 10.1002/chem.202102343

DO - 10.1002/chem.202102343

M3 - Article

C2 - 34632666

AN - SCOPUS:85117387590

SN - 0947-6539

VL - 27

SP - 16512

EP - 16522

JO - Chemistry - A European Journal

JF - Chemistry - A European Journal

IS - 66

ER -

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

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