Steady-state and time-resolved spectroscopic investigations on the existence of stable methanol/AOT/n-heptane reverse micelles

• The existence of stable methanol/AOT/n-heptane reverse micelles is confirmed.
• Photophysics of the coumarin 153 in methanol/AOT/n-heptane and methanol/n-heptane is compared.
• Emission spectra show excitation wavelength dependence in reverse micelles.
• The decay curves of coumarin 153 are biexponential in reverse micelles.
• Excited-state hydrogen bonding facilitates radiationless deactivation pathways.

In this work, we have reported our study on the controversial issue whether methanol molecules can be effectively encapsulated by surfactant AOT to form true reverse micelles. We compared the different photophysical properties of coumarin 153 (C153) in methanol/AOT/n-heptane reverse micelles and methanol/n-heptane binary mixture by means of steady-state absorption, fluorescence and time-resolved fluorescence spectroscopies. In the reverse micelles, the fluorescence emission spectra of C153 were dependent on the excitation wavelength, while in binary mixtures, the excitation wavelength dependence was not observed. The biexponential decay curves of C153 in reverse micelles give a further confirmation for the two different environments where C153 molecules reside in. In other words, C153 molecules can exist both inside the core of the reverse micelles and outside of it. These results proved that the methanol can be effectively encapsulated by AOT in n-heptane solvents to form stable methanol/AOT/n-heptane reverse micelles.

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