Cucurbit[8]uril/Cucurbit[7]uril Controlled Off/On Fluorescence of the Acridizinium and 9‐Aminoacridizinium Cations in Aqueous Solution

Abstract

The blue fluorescence of acridizinium bromide (ADZ+) and the green fluorescence of 9-aminoacridizinium bromide (AADZ+) in aqueous solutions can be almost entirely switched off upon the double inclusion of these guests in the cavity of cucurbit[8]uril (CB[8]) owing to the formation of a nonfluorescent, noncovalent dimer complex, and then fluorescence can be effectively restored by adding cucurbit[7]uril (CB[7]) to the complex because it competitively extracts the fluorophores out of the CB[8] cavity.

Control of the Supramolecular Excimer Formation of Thioflavin T within a Cucurbit[8]uril Host: A Fluorescence On/Off Mechanism

“…[3][4][5][6][7][8] Apart from forming stable 1:1 complexes with varieties of cationic dyes, [5][6][7]9] the higher analogues like cucurbit [8]uril (CB8) are credited with forming higher stoichiometric complexes by co-localizing p-stacked or charge-transfer pairs in the cavity. [2,[10][11][12] This feature has been favourably exploited in the design and synthesis of photofunctional materials, molecular architectures like molecular necklaces, machines, and fluorescent on/off switches. [2,10,12] Extensive modulations in the photophysical characteristics of the guest molecules, resulting from its positioning in the host cavity, are of great importance in sensing local microenvironments and improving its functionality.…”

“…[2,[10][11][12] This feature has been favourably exploited in the design and synthesis of photofunctional materials, molecular architectures like molecular necklaces, machines, and fluorescent on/off switches. [2,10,12] Extensive modulations in the photophysical characteristics of the guest molecules, resulting from its positioning in the host cavity, are of great importance in sensing local microenvironments and improving its functionality. Localizing one such potential extrinsic dye, Thioflavin T (ThT), into the structural cavities of protein fibrils has been extensively applied in the early detection of amyloid fibril formation in tissues to diagnose chronic disorders such as Alzheimers and Parkinsons diseases.…”

Insight into Unusual Downfield NMR Shifts in the Inclusion Complex of Acridine Orange with Cucurbit[7]uril

“…Note that these induced NMR shifts of the AO protons in the presence of CB [7] were in sharp contrast with those associated with the inclusion of other organic molecules in the CB [7] cavity, with upfield shifts of their proton resonances. [26][27][28][29][30] It was known that Cob + could be completely included in the CB [7] cavity with an upfield shift of its proton resonance. [38] Upon addition of Cob + to the AO·CB [7] complex, the NMR spectrum of the aqueous AO solution was completely recovered, along with an upfield shift of the Cob + proton resonance.…”

“…[25] 1 H NMR spectroscopy is one of the most effective tools for studies of complex formation between CB[n]s and organic molecules. [26][27][28][29][30] In general, downfield shifts of the resonances of guests result from the deshielding effects of the carbonyl groups of the CB[n]s when the portions of the guests are located in the portals, whereas upfield shifts indicate that the guests are encapsulated in the shielding hydrophobic cavities. However, low dye concentrations commonly prevent detailed NMR characterization.…”

Interactions between photoacidic 3-hydroxynaphtho[1,2-b]quinolizinium and cucurbit[7]uril: Influence on acidity in the ground and excited state

“…1) represents an efficient water-soluble photoacid (p K a = 7.2; p K a * < 0) [35]. Furthermore, it was observed that quinolizinium derivatives 1b and 1c bind to cucurbiturils with high affinity [36–37]. Therefore, it seemed possible that the available range of p K a and p K a * values of this class of compounds can be extended by complexation with an appropriately sized CB[ n ].…”