Kinetics Inside, Outside and Through Cucurbiturils

Abstract

This review describes the kinetics at play in Cucurbituril (CB[n])/guest recognition within a very wide time frame, from picoseconds to days. We cover the kinetics of (1) radiative and non‐radiative decays of fluorophores inside and outside CB[n]s, (2) guest motions in the CB[n] cavity, and (3) ingression, egression and threading mechanisms into, out of and through the macrocycles. We then show that the kinetics of guest release or capture can be controlled using CB[n]‐capped mesoporous systems and micelles, or by coupling those processes to the kinetics of ancillary reactions. The last section is devoted to the latest examples of reactions catalyzed and inhibited by CB[n]s.

Photo/redox-responsive 2D-Supramolecular assembly involving Cucurbit[8]uril and a star-shaped porphyrin tecton

“…[43] As can be seen in the early stage of the titration (Figure 3), the threading of a non-symmetrical viologen-based axle through CB [7] also results in the splitting of the Hi protons, observed as two partially overlapped doublets (pseudo triplet at 5.80 ppm) in the spectrum of the inclusion complex. The effect of the viologen-based guests on the CB [7] hosts is further revealed on the spectrum recorded at low concentration of 1Zn 8+ (0.1 mM) in the presence of 8 equivalents of CB [7] (top spectrum in Figure 3 A similar investigation has been carried out with the less soluble CB [8] host, featuring a wider inner cavity but still capable of forming 1/1 inclusion complexes with viologens derivatives [34,44,45]. The stoichiometry and structure of the assembly is also deduced from the titration data depicted in Figure 4.…”

Dynamic supramolecular polymers built from cucurbit[n]urils and viologens

“…From a thermodynamic point of view, the exceptionally high affinity of CB[ n ]s for positively charged organic guests in water is attributed to a combination of factors including the desolvation of the guest, the ejection of ‘high energy’ water molecules trapped inside CB[ n ]s prior to encapsulation, and ion–dipole interactions between the carbonyl functions at the cavity portal and any positively charged parts of the guest. In most cases only one guest can be fitted within the cavity of the smallest CB[ n ] ( n = 5, 6, 7) while the larger cavity of CB[8] can potentially accommodate two or even three guests …”

“…In most cases only one guest can be fitted within the cavity of the smallest CB[n] (n = 5, 6, 7) while the larger cavity of CB [8] can potentially accommodate two or even three guests. [30][31][32][33][34][35] Most efforts in the field of supramolecular chemistry have focused on CB [8], on account of its ability to accommodate two -conjugated guests tightly interacting inside the barrel-shaped cavity in the form of cofacial charge transfer complexes. 36 The opportunities are more limited for the smallest analogs CB [5], CB [6] and CB [7], whose inner cavities only allow hosting single guests.…”

Directional Self‐Sorting with Cucurbit[8]uril Controlled by Allosteric π–π and Metal–Metal Interactions

“…As far as emissions are concerned, blueshifts, reduced Stokes shifts and fluorescence enhancements are frequently observed upon guest encapsulation by CB[ n ], as the polarity and polarizability of the macrocycles are low, and encapsulation limits nonradiative decay from the excited state through solvent relaxation . To the best of our knowledge, we report here for the first time the effect of CB[ n ] encapsulation on the phosphorescence of a chromophore.…”