Exploration of Self-Aggregation of Coumarin 7 and Coumarin 30 in Water: Role of β-Cyclodextrin as a Modulator

Abstract

Steady-state and time-resolved spectroscopic studies demonstrate that two members of the coumarin class of dyes, coumarin 7 (C7) and coumarin 30 (C30), undergo self-aggregation in water. The development of hypsochromically shifted new absorption bands in addition to the existing monomer bands with an increase in concentration of the dyes in an aqueous medium suggests that the aggregates are of H-type. An absorption-based kinetic study reveals that the rate of aggregation of C30 is an order of magnitude faster than that of C7. Second-order rate kinetics, as obtained from the half-life (t 1/2) data, implies that the aggregates are dimeric in nature. Observations of isosbestic points in area-normalized absorption spectra (ANAS) and isoemissive points in area-normalized fluorescence excitation spectra (ANFES) and time-resolved area-normalized emission spectra (TRANES) establish that ground-state monomer ⇌ dimer equilibria for both of the systems are preserved in the photoexcited state. The present study further establishes that β-cyclodextrin is the most efficient of the three common cyclodextrins in shifting the equilibria toward the monomer by encapsulating the monomers within its cavity, making β-CD a convenient modulator to control the self-aggregation process. Dynamic light scattering (DLS), quantum chemical calculations, and molecular docking studies provide further support to our propositions.

Disaggregation-induced resurgence of quenched emission of a self-assembled bis-indole system: photophysics, energetics, and dynamics

“…All the absorption spectroscopic results signified the disaggregation of BIPM self-associations into monomers in b-CD environments and the probable formation of BIPM-b-CD inclusion complexes. These results were quite similar to the absorption spectroscopic changes for the aggregation-disaggregation of coumarin 7 and coumarin 30 in the presence of b-CD that were recently observed by Das et al 4 During aggregation, the natural and unperturbed excited states of the closely spaced indole chromophoric units in BIPM linearly coupled to form new excitonic states. 7 The electronic excitation of BIPM aggregates was actually its activation into exciton coupled states that resulted in the broadness and loss of fine structure of its absorption spectrum.…”

“…26 However, studies on CDs to control dye aggregation and recover probe fluorescence are limited. 4–6,27,28 In this context, the present study demonstrates the recovery of quenched fluorescence from the nanoclusters of an organic probe through their disaggregation and subsequent β-CD encapsulation.…”

“…Disaggregation of molecular associations suffering from aggregation caused quenching (ACQ) of emission is one of the preeminent instances where pleasant outcomes are resulted. [1][2][3][4][5][6] Several fluorescent dyes with planar and polycyclic p-conjugated frameworks undergo self-aggregation (through p-p stacking, van der Waals' interaction, or H-bonding), and their emission efficiencies decrease, which limits their applications. [7][8][9] Therefore, the development of appropriate strategies to control and minimize molecular aggregations is crucial.…”

“…[7][8][9] Therefore, the development of appropriate strategies to control and minimize molecular aggregations is crucial. Although various chemical and physical strategies have been adopted to prevent the aggregation of dyes, [3][4][5][6][10][11][12][13][14][15] their effects are often temporary, complicated, and might perturb the electronic conjugation of the fluorophores, which results in unwanted effects on their emission properties. 15 Therefore, the development of simple, effective, and sustainable strategies for the disaggregation of molecular assemblies to recover emission efficiency is of special interest.…”

Dual Stimuli-Responsive BSA-Protected Silver Nanocluster-Driven “FRET On–Off” within the Niosomal Membrane: An Amalgamation of Restoration of Aggregation-Induced Quenched Fluorescence and Energy Transfer

“…Self-aggregation of coumarin dyes is readily observed in several occasions due to the structural features of the molecule. − Typically, the planar coumarin skeletons are susceptible to aggregation via strong π–π stacking interactions leading to aggregation-caused quenching (ACQ) of photoluminescence (PL) and weakening the activity of optoelectronic devices and many other exciton-controlled performances. ,,, The coumarin member used in the present study is C6 (Figure A) that aggregates readily in water even at 1 μM concentration and hence substantially loses its PL . However, this lost PL can be revived by several host–guest chemistry-based techniques following hydrophobic interactions. − Hence, we have applied the multilamellar niosome vesicles that followed the same mechanism to disintegrate the aggregated C6 molecules, which encapsulate inside the membrane (Figure A), and hence the lost PL is revived (Figure B).…”