Assembly and Applications of Macrocyclic-Confinement-Derived Supramolecular Organic Luminescent Emissions from Cucurbiturils

Cucurbit[n]urils (Q[n]s or CB[n]s), as a classical of artificial organic macrocyclic hosts, were found to have excellent advantages in the fabricating of tunable and smart organic luminescent materials in aqueous media and the solid state with high emitting efficiency under the rigid pumpkin-shaped structure-derived macrocyclic-confinement effect in recent years. This review aims to give a systematically up-to-date overview of the Q[n]-based supramolecular organic luminescent emissions from the confined spaces triggered host-guest complexes, including the assembly fashions and the mechanisms of the macrocycle-based luminescent complexes, as well as their applications. Finally, challenges and outlook are provided. Since this class of Q[n]-based supramolecular organic luminescent emissions, which have essentially derived from the cavity-dependent confinement effect and the resulting assembly fashions, emerged only a few years ago, we hope this review will provide valuable information for the further development of macrocycle-based light-emitting materials and other related research fields.

Photophysical Activity and Host-Guest Behavior of Ruthenium Polypyridyl Catalysts Encapsulated in Cucurbit[10]uril

This work outlines a strategy to combine the use of visible light and confined spaces to form a supramolecular photocatalyst system. Polypyridyl ruthenium(II) complexes [Ru(bpy)₃]²⁺ (bpy = 2,2'-bipyridine), [Ru(bpy)₂(bpm)]²⁺ (bpm = 2,2'-bipyrimidine), and [Ru(bpy)₂(bpz)]²⁺ (bpz = 2,2'-bipyrazine) are encapsulated in cucurbit[10]uril to form host-guest systems in aqueous solution. The photophysical properties of the complexes are altered by encapsulation, with improved emissive behavior for the heteroleptic complexes. Oxidative quenching of the photocatalyst's excited state via intermolecular charge transfer to methyl viologen can occur within the internal cavity, which acts to preorganize the reagents. The host-guest system containing [Ru(bpy)₃]²⁺ can bind suitable substrates, and essential criteria for its use as a supramolecular photocatalyst are investigated.

Interaction of the Large Host Q[10] with Metal Polypyridyl Complexes: Binding Modes and Effects on Luminescence

Aqueous solution state host-guest systems have been studied, comprising the large host cucurbit[10]uril with luminescent cationic tris(polypyridyl) (PP) metal complexes [Ru(PP)₃]²⁺ and [Ir(PP)₃]³⁺. All complexes bind strongly with the host, with the overall complex charge and size having a minor effect on affinity but influencing the association dynamics and contribution from higher-order (1:2) host-guest species. The 1:2 species contributes more significantly to the binding equilibrium in the case of [Ru(phen)₃]²⁺. The effect of the host upon emission is highly variable and depends on the electronic structure of the guest. The metal-to-ligand charge transfer (MLCT) emission of [Ru(PP)₃]²⁺ is strongly quenched, in contrast to the large enhancements seen previously for MLCT emission of iridium cyclometalated complexes, while the ligand-centered emission of [Ir(PP)₃]³⁺ is little affected. The mechanisms of quenching and enhancement are discussed, together with the implications for the design of larger supramolecular assemblies based on these archetypal emitters.

Ramachandran A, Mohamed AP, Pillai S. Photonic band gap effect and dye-encapsulated cucurbituril-triggered enhanced fluorescence using monolithic colloidal photonic crystals

Enhanced fluorescence was achieved by tuning the photonic band gaps in colloidal photonic crystals and host–guest chemistry.

Alkyl substituted 4-pyrrolidinopyridinium salts encapsulated in the cavity of cucurbit[10]uril

The interaction between cucuribit[10]uril (Q[10]) and a series of 4-pyrrolidinopyridinium salts bearing aliphatic substituents at the pyridinium nitrogen, namely 4-(C₄H₈N)C₅H₅NRBr, where R = Et (g1), n-butyl (g2), n-pentyl (g3), n-hexyl (g4), n-octyl (g5), n-dodecyl (g6), has been studied in aqueous solution by ¹H NMR spectroscopy, electronic absorption spectroscopy and mass spectrometry.

Modelling the luminescence of iridium cyclometalated complexes encapsulated in cucurbituril

Iridium(iii) cyclometalated complexes in aqueous solution often display relatively weak luminescence. It has been shown in previous work that this emission can be significantly enhanced (by up to two orders of magnitude) by encapsulation in cucurbit[10]uril (Q[10]). Luminescence lifetime measurements suggest a dynamic self-quenching mechanism is active, possibly due to displacement of an excited guest complex via collision with an unbound complex. We devise a model for the association of a group of iridium(iii) cyclometalated complexes with Q[10]. The model parameters are then fitted to steady-state emission titration curves. The excellent agreement of experimental data with the model provides valuable mechanistic information relating to the way this class of metal complexes interact and associate with the Q[10] host.

New class of artificial enzyme composed of Mn-porphyrin, imidazole, and cucurbit[10]uril toward use as a therapeutic antioxidant

In this study, we investigated a new class of artificial enzymes composed of Mn-porphyrin, imidazole, and cucurbit[10]uril (CB[10]) toward therapeutic antioxidants.

Supramolecular Assemblies of Cucurbit[10]uril Based on Outer Surface Interactions

Using an established method, we isolated a large quantity of cucurbit[10]uril (Q[10]) and prepared Q[10]-based supramolecular assemblies via different approaches. For example, the structure-directing agent [CdCl4]2– was used or the Q[10] molecule itself acted as a self-structure-directing agent to form different Q[10]-based supramolecular assemblies through the outer surface interaction of Q[10]. Generally, the Q[10]-based supramolecular assemblies possess porous features that suggest that Q[n]-based compounds could be used to manufacture molecular sieves and sensors and applied in absorption and separation technologies.

Interactions of cucurbit[6,7]urils with human serum albumin and their effects on zaltoprofen transportation

Interference of CB[6,7]s on a HSA–zaltoprofen binding system was studied for conducting the applications of CB[6,7]s.

Solid-state study of the structure and host–guest chemistry of cucurbituril-ferrocene inclusion complexes

Solid-state host–guest interactions have been investigated for cucurbit[n]uril-ferrocene inclusion compounds (n = 7, 8) prepared via a microwave-assisted hydrothermal approach.

Formylated chloro-bridged iridium(iii) dimers as OLED materials: opening up new possibilities

In this study, a series of four formyl-substituted chloro-bridged iridium(iii) dimers were prepared.