Influence of double confinement on photophysics of 7-(diethylamino)coumarin-3-carboxylic acid in water/AOT/isooctane reverse micelles

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.