Excited-State Behavior of 7-Diethylaminocoumarin Dyes in AOT Reversed Micelles:  Size Effects

Abstract

Photophysical properties of two 7-diethylaminocoumarin dyes belonging to the family of coumarinylbenzopyrano pyridines (BC I and BC II), and a third dye, 7-diethylamino-4-trifluoromethyl coumarin (C 35), are reported in Aerosol OT (AOT) and water-in-oil (n-heptane/AOT/water) microemulsions. In the case of BC I, emission arising from two different environments for the dye is observed. Results of the steady-state fluorescence anisotropy experiments also support the presence of two different environments. At low W 0 ()[water]/[AOT]) values (0 < W 0 < 10), the excited-state properties of the molecule in the interfacial region are found to be sensitive to the polarity of the surrounding microenvironment. The decrease in the fluorescence quantum yield at higher W 0 (g10) values can be attributed to the intermolecular hydrogen bonding between the cyano (-CN) group of the dye and water molecules present in the micellar interface. These observations are explained on the basis of the comparable size of the probe dye molecule and the molecular dimensions of the interfacial region in the microemulsions. The large molecular size of BC II is also found to be the reason for the sensitivity of the dye to the microenvironment of n-heptane/AOT/water microemulsions. However, the effects are much smaller than those observed in BC I. A similar photophysical study involving C 35 is found to show no such effects. The smaller molecular size, charge neutrality, hydrophobic nature, and a preferential solvation in heptane are essentially the reasons for the results observed in C 35.

Comparison between Two Anionic Reverse Micelle Interfaces: The Role of Water–Surfactant Interactions in Interfacial Properties

“…Our results challenge this expectation because, as was demonstrated, acid-base equilibriums change dramatically at the RM interfaces due to the enormous ionic strength. [8,47] Moreover, we did not see the OÀH stretching frequency of the nonionized phosphoric group at any W 0 values investigated.…”

“…[3][4][5][6][7] The interfacial region is known to have high ionic strength and a heterogeneous micropolarity. [8] The dialkyl phosphates and their alkaline salts are of interest in extraction processes because of their complexing properties toward metal ions and are important in hydrometallurgy, the nuclear industry, and biological materials. [9] Among them, sodium bis(2-ethylhexyl) phosphate (NaDEHP, Scheme 1) has the particular property to give rise to RMs in organic solvents, as first pointed out by Eicke and Christen.…”

Distribution of amines in water/AOT/n-hexane reverse micelles: influence of the amine chemical structure

“…either inside the pool (free) or at the interface (bound) change with W 0 [4][5][6][7][8]. The interfacial region is also known to have high ionic strength and a heterogeneous micropolarity [1,9].…”

Synthesis of novel coumarin and benzocoumarin derivatives and their biological and photophysical studies

“…Synthesis of Novel Coumarin and Benzocoumarin Derivatives 1295 solvents depending on the substituent, and so this chromophore appears sensitive to its environment [43]. For coumarin with two fused rings (i.e.…”