Incorporation of Coumarin 6 in cyclodextrins: microcrystals to lamellar composites

Abstract

Coumarin 6 precipitates in water as microcrystals resulting in a considerable loss in fluorescence yield. Differential interaction of the microcrystals with cyclodextrins of different cavity size enhances the fluorescence yield of the dye by 160 fold in some cases. Highly fluorescent ultrathin lamellar entities form through hydrogen bonding. † Electronic supplementary information (ESI) available: Structure of C6, AFM and SEM images of C6 aer incubation in water (with 1% methanol) for 30 minutes at room temperature, uorescence spectra of C6 in a-, band g-CDs in aqueous environment and time resolved uorescence decay prole for C6 in presence of band g-CDs. See

Revival of the nearly extinct fluorescence of coumarin 6 in water and complete transfer of energy to rhodamine 123

“…3). Absorbance at 500 nm, due to the aggregates, [20][21][22] remains structurally unchanged upon addition of SDS up to B6 mM, indicating the existence of the aggregates under pre-micellar conditions. The spectrum changes abruptly at and above 8 mM SDS concentration where the absorption band due to the aggregates starts disappearing.…”

“…24 The faster component is for the intramolecular charge transfer (ICT) in C6. 21 Table 1 provides the excited state lifetimes of C6 under different conditions in an aqueous environment. In water, the C6 microcrystals have p-p stacking interactions and hence a fast decay component is observed.…”

“…C6, however, has a tendency to form microcrystals through H-type aggregation in solution. [20][21][22] Early reports suggested the generation of C6 microcrystals through the reprecipitation method using a concentrated solution of the dye in acetone at room temperature with a large volume of water. 20 Later, our group established that even at micromolar concentration and in an aqueous medium, C6 quickly forms microcrystals (Fig.…”

“…2). 21 The C6 microcrystals formed in water lead to quick loss in C6 fluorescence and hence their applications become limited. In some of our previous studies, we have reported ways to retrieve C6 fluorescence through guest-host chemistry in an aqueous medium.…”

“…In some of our previous studies, we have reported ways to retrieve C6 fluorescence through guest-host chemistry in an aqueous medium. 21,23 Herein, we state that C6 fluorescence can be revived by using micelles in water followed by nearly complete transfer of the energy absorbed from light to an acceptor through Förster resonance energy transfer (FRET).…”