Fluorescence Studies of the Hydrogen Bonding of Excited‐State Molecules within Supramolecular Host–Guest Inclusion Complexes

Cucurbit[8]uril-templated H and J dimers of bichromophoric coumarin dyes: origin of contrasting emission

“…1 For such molecular assemblies, while the processes of assembly or disassembly at molecular level is governed by 15 non-covalent interactions such as hydrogen bonding, π-stacking, van der Waals or solvophobic forces, the ensuing photophysical attributes are dictated by spatial arrangement, rigidity etc originating from the structural aspects of the constituents. 2, 3 Therefore, gaining control over these noncovalent interactions 20 and the molecular orientation/stacking parameters are crucial for management of optical properties of the fluorophores or its aggregates 4 and can be accomplished by introducing, more specifically, macrocyclic hosts. 5 Among various synthetic cavitand receptors, the cyclic oligomers obtained in the acid 25 catalysed condensation of glycoluril with formaldehyde, known as Cucurbit[n]uril (CBn, n = 5-8, 10,14) family of macrocyclic hosts, attracted a great deal of attention due to their hydrophobic cavity with carbonyl laced portals at either ends, which offer strong ion dipole interaction for cationic guests, such as organic 30 or organometallic cationic moieties, metal ions/complexes, etc.…”

Molecular‐Recognition‐Assisted pKa Shifts and Metal‐Ion‐Induced Fluorescence Regeneration in p‐Sulfonatocalix[6]arene‐Encapsulated Acridine

“…This is in contrast to the general observations made using other macrocycles such as cyclodextrins (CDs) and cucurbiturils, for which the altered (less polar) microenvironment inside the macrocyclic host cavities and/or a spatial confinement limits alternative nonradiative pathways. [7,26] In this context, the strong fluorescence quenching observed in the case of acridine in the presence of SCX6 is very intriguing because these changes represent an inclusion complex formation between them. However, the possibility of a small percentage of exclusion complex formation between SCX6 and the dye cannot be ruled out.…”

Modulation of Protolytic Equilibrium of Bichromophoric Coumarin‐30 Dye with Cucurbit[8]uril Encapsulation

“…The noncovalent interactions of guest molecules with preorganized hosts often lead to the modulation of chemical as well as physical properties of the encapsulated guests. [1,2] This elegant noncovalent approach to tune the intrinsic molecular properties has attracted much attention from various research communities. Host-guest chemistry is widely utilised in a range of applications such as sensing, on-off switches, [3,4] photostabilization, [5,6] supramolecular catalysis, [6][7][8] drug delivery vehicles, [9] enzymatic assay, [10] nanocapsules, [11] and other supramolecular architectures.…”

“…[9] Guest molecules with intrinsic fluorescence respond to such complexation induced supramolecular pK a shifts because the photophysical aspects of fluorogenic molecules are inherently related to their chemical identity. [2] Therefore, to explain the photophysical modulations in the presence of a nonfluorescent CBn host, it is essential to have the clear view of the acid-base equilibrium of an encapsulated guest. With our continuous effort in this direction, taking advantage of the supramolecular pK a shift and its response to external stimuli such as metal ions, we have demonstrated the salt-induced relocation of the neutral red dye from the macrocyclic cavity of CB7 into the biomolecular pocket of bovine serum albumin.…”