Abstract
The effect of double confinement on the photophysics of 7-(diethylamino)coumarin-3-carboxylic acid (7-DCCA) inside the water pool of water/AOT/isooctane reverse micelles has been reported in this study. At first a supramolecular host–guest complex was formed in water between 2-hydroxypropyl-γ-cyclodextrin (HP-γ-CD) and 7-DCCA. Then the aqueous solution of this complex was used to form reverse micelles at any particular w0 value (w0 = [water]/[surfactant]). We have used sodium dioctyl sulfosuccinate (AOT) as surfactant and isooctane as non-polar solvent to prepare reverse micelles. A comparative study between double confinement system and the single confinement system, where the 7-DCCA molecule was incorporated inside the core of the water/AOT/isooctane reverse micelles, was done. We have used the steady state absorption and fluorescence emission techniques to highlight the significant shift of the spectral behaviour of the 7-DCCA due to the double encapsulation of the dye in the nanopool of the reverse micelles. More affirmation has been achieved by the use of time resolved fluorescence emission spectroscopy. The study of solvation dynamics and rotational relaxation dynamics was used as tools to investigate the effect of double encapsulation on the excited state dynamics of the probe molecule. These excited state dynamics clearly show that even at the highest w0 value studied here, the excited state dynamics of the doubly confined dye are significantly different from those of the single confined dye in the reverse micelle. The higher values of fluorescence emission decay time, rotational relaxation and solvent relaxation times in the doubly confined system compared to those of the single confined system at different w0 values proved the existence of the supramolecular host–guest complex inside the core of the water/AOT/isooctane reverse micelle.
Highlights
Coumarin has been a very popular class of compound; due to its excellent optical properties it has been used in several photophysical studies.[1,2,3] Substituted amino coumarins have been used as popular uorescence probe molecules in several studies due to their sensitivity to the environment.[4,5,6,7] The photophysical properties of 7-aminocoumarins are dependent on the polarity and viscosity of the media and on the speci c solute solvent interaction with the media
We have found in our system that for w0 1⁄4 3 the uorescence decay time of 7-(diethylamino) coumarin-3-carboxylic acid (7-DCCA) is greater for doubly con ned complex than the singly con ned dye inside the water/Aerosol OT (AOT)/isooctane reverse micelle at the same w0 value
The uorescence decay times showed the effect of double con nement on the photophysics of 7-DCCA in the reverse micelles
Summary
Coumarin has been a very popular class of compound; due to its excellent optical properties it has been used in several photophysical studies.[1,2,3] Substituted amino coumarins have been used as popular uorescence probe molecules in several studies due to their sensitivity to the environment.[4,5,6,7] The photophysical properties of 7-aminocoumarins are dependent on the polarity and viscosity of the media and on the speci c solute solvent interaction with the media. The last category of water molecules inside the pool comprises of free water molecules, these are strongly hydrogen bonded They represented that with the gradual addition of water to the reverse micelle core the number of bound water molecules per AOT surfactant molecule increased regularly upto w0 z 18, beyond this it remained constant. This study will help us to understand the modi cation and improvement of photophysical properties of a hydrophilic and TICT forming dye (like 7-DCCA) upon a double con nement in the reverse micelles. For this purpose we have used the uorescence emission properties of 7-DCCA as tool. We have compared our result with our previous study,[47] where we had demonstrated the effect of single con nement on the photophysics of 7-DCCA in the reverse micelles
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