Probing the interface polarity of AOT reversed micelles using centro-symmetrical squaraine molecules

Abstract

The solvatochromism of both absorption and emission spectra of two centro-symmetrical squaraine dyes was studied in pure solvents, dioxaneÈwater mixtures and AOT (Aerosol OT, bis(2-ethylhexyl)sodium sulfosuccinate) reversed micelles. The shifts observed in pure solvents are relatively large and are associated with non-negligible soluteÈsolvent polar interactions. Good empirical correlations with the n* polarity scale (a measure of the solvent dipolar character) and with the solvent proticity a scale (a measure of the solvent acidity character) were obtained. Preferential solvation by water was not observed in the dioxaneÈwater mixtures enabling the calculation of n*, a and polarity scale values, the latter in a good agreement with E T 30 literature values. Similar trends of these parameters in AOT reversed micelles were found, but some deviations are observed at low water contents due to probe distribution at two di †erent interfacial sites.

The Influence of Water on the Photophysical and Photochemical Properties of Piroxicam in AOT/iso-octane/Water Reversed Micelles

“…Absorption and emission maxima were correlated with Kamlet-Taft parameters and fluorescence quantum yield was correlated with both solvent viscosity and E T (30). The use of such correlations to obtain solvent parameters of water encapsulated inside reversed micelles has been tried (34)(35)(36). In this case it was possible to have an idea of the probe's environment through the calculation of E T (30) and microviscosity which were compared with values from the literature.…”

Electric polarization effects on the electronic spectral shift of centrosymmetric compounds

“…It has been reported that the dielectric dipolar BMO model is the best one at expressing the solvatochromism of centrosymmetric molecules, which do not have dipole moment [14][15][16][17]. The possibility that the correlation formed therein was due to the solute quadrupole moment and the solvent permanent dipole moment interactions was previously advanced [15,16].…”

“…It has been reported that the dielectric dipolar BMO model is the best one at expressing the solvatochromism of centrosymmetric molecules, which do not have dipole moment [14][15][16][17]. The possibility that the correlation formed therein was due to the solute quadrupole moment and the solvent permanent dipole moment interactions was previously advanced [15,16]. Theoretical investigations, like quantum mechanics studies [3,18,19] or molecular mechanic calculations [20], have extended the Onsager concept to a multipole in a spherical cavity, not only to dipole, but quadrupole, octupole, and so on.…”

“…Thus, it is likely that some correlation would be observed in the dipolar BMO model for the cases where the quadrupole moment might be significant. Nevertheless, the solvatochromic shift of centrosymmetric molecules has not yet become a standard tool and only few cases have been reported [14][15][16][17]21,22].…”

Reactivity and Dynamics at Liquid Interfaces

“…Unless most of the solute molecules are at the interface, which is the case for systems like adsorbed monolayers, micelles and microemulsions, [348][349][350][351][352][353][354] Because a non-resonant term also contributes to the signal, the peak of the observed SHG spectrum does not necessarily matches the electronic transition energy, so it must be removed by a fitting procedure. 355 SHG has been used mainly to measure solute surface concentration, molecular orientations and relaxation, as mentioned earlier.…”