Many fluorescent chromophores have been employed to investigate the nature and dynamics of the water confined in reverse micelles (RMs). However, some questions remain as to the location of a probe in a RM and the diameter of the RM at which the physical characteristic of the water inside RMs becomes similar to that of bulk water. In this work, we systematically studied the photophysics of IR125 and C152 in AOT RMs at different w0 by means of static absorption and fluorescence spectroscopy as well as time-resolved fluorescence spectroscopy. We obtained the absorption maxima, fluorescence emission maxima, fluorescence lifetime, and reorientation time of IR125 and C152 in AOT RMs at corresponding w0. We found that all obtained photophysical parameters of IR125 and C152 in AOT RMs as a function of w0 have a distinct changeover point around w0 = 8, indicating that there is a dramatic change in the nature of the water confined in AOT RMs around w0 = 8. The observed changeover point around w0 = 8 is well in agreement with the Satpati's report (ChemPhysChem, 2009, 10, 2966). In addition, we observed that the measured reorientation time of IR125 in AOT RMs increases with the increase of w0, which is opposite to the trend of change in the measured reorientation time of C152 in AOT RMs with the increase of w0. We found that IR125 prefers to reside in the water pool of AOT RMs and that C152 prefers to reside in the outer side of the interfacial region or the nonpolar n-heptane phase of AOT RMs. Furthermore, we found that the time-resolved fluorescence anisotropy of IR125 in smaller w0 AOT RMs primarily measures the reorientation of RMs and the time-resolved fluorescence anisotropy of IR125 in larger w0 AOT RMs measures the reorientation of IR125 in the water pool confined in RMs. This work demonstrated that IR125 is an excellent probe to study the nature and dynamics of the water confined in AOT RMs.
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