Triple Emission from p‐Dimethylaminobenzonitrile–Cucurbit[8]uril Triggers the Elusive Excimer Emission

Abstract

The intriguing dual-emission behavior of p- dimethylaminobenzonitrile (DMABN) and the identity of the associated excited states is, arguably, the most extensively investigated and also controversially discussed molecule- specific phenomenon of modern photochemistry. We have now found a new, third fluorescence band when DMABN is encapsulated within the water-soluble molecular container cucurbit[8]uril (CB8). It is centered between the previously observed emissions and assigned to the elusive excimer emission from DMABN through 1:2 CB8:DMABN complex formation. Heating of the CB8⋅(DMABN)2 complex from 0 to 100 °C results in the dissociation of the ternary complex and restoration of the dual-emission properties of the monomer. Alternatively, monomer emission can be obtained by selecting cucurbit[7]uril (CB7), a host homologue that is too small to accommodate two DMABN molecules, or by introducing ethyl instead of methyl groups at the amino terminus of the aminobenzonitrile guest.

Cucurbituril As A Versatile Tool to Tune the Functions of Proteins

“…Cucurbiturils are a series of supramolecular macrocyclic hosts with n glycoluril bridged by 2n methylenes, yielding cucurbituril series (CB [5,6,7,8,10,13,14,15]). CB [5][6][7][8][9][10] (except for CB [13][14][15]) share a common pumpkin-shaped structure with a large hydrophobic cavity and two negatively charged portals.…”

“…CB [5][6][7][8][9][10] (except for CB [13][14][15]) share a common pumpkin-shaped structure with a large hydrophobic cavity and two negatively charged portals. [26][27][28][29] Crystal structures indicates that the four biocompatible CB[n]s, such CB, [5] CB, [6] CB [7] and CB [8] have the same height of 9.1 Å and diverse outer diameters ranging from 13.1 Å -17.5 Å .According to the sizes of the cavities, the smaller cucurbituril of CB [5] can complex with some metal cations and gas molecules. In contrast, the larger CB[n]s such as CB[6&7] and CB [8] can complex with one and two organic guests respectively.…”

“…Prior to tuning their activities, covalent methods such as click reactions and Snap-tag serve as efficient methods to link the components into proteins. [5] CB [7] and CB [8] can tune the activities of methylene blue by complexation with dye and hydroxyl radicals in Fenton-mediated oxidation. To address the challenge, supramolecular hosts with the recognition motifs and cavities, typical of pillararenes, cyclodextrins, cucurbiturils, have been developed to recognize and bind strongly toward special guest molecules.…”

Supramolecular Assemblies of Cucurbiturils with Photoactive, π‐conjugated Chromophores

“…Upon encapsulation of dyes by CB7s, a spectral shift is observed as well as an increase in their fluorescence quantum yields, enhanced brightness and photostability. [20] One of the most important effects of CBs on the photoactive chromophores is an increase in their fluorescence quantum yields. The high affinity of the carbonyl decorated portals of CBs towards cations results in a considerable shift of protonation equilibria and assists the protonation of fluorescent dyes.…”

pH-Assisted control over the binding and relocation of an acridine guest between a macrocyclic nanocarrier and natural DNA

“…To verify such a stoichiometry further for the host-guest complexes in the AcH + -DNA and Ac-DNA systems, we carried out Job's plot measurements 42,43 following both absorption and fluorescence studies. To verify such a stoichiometry further for the host-guest complexes in the AcH + -DNA and Ac-DNA systems, we carried out Job's plot measurements 42,43 following both absorption and fluorescence studies.…”