Intramolecular Charge Transfer Reaction, Polarity, and Dielectric Relaxation in AOT/Water/Heptane Reverse Micelles: Pool Size Dependence

Abstract

Intramol. charge transfer (ICT) reaction in a newly synthesized mol., of 4-(41-morpholinyl) benzonitrile (M6C), in AOT/water/heptane reverse micelles at different pool sizes has been studied by using steady-state and time-resolved fluorescence emission spectroscopy. The pool size dependences of the reaction equil. const. and reaction rate have been explained in terms of the av. polarity of the confined solvent pools estd. from the fluorescence emission Stokes shift of a nonreactive probe, coumarin 153, dissolved in these microemulsions. The complex permittivity measurements in the frequency range 0.01 ≤ ν/GHz ≤ 2 for these microemulsions at different pool sizes (0 ≤ w ≤ 40) and AOT concns. (0.1 ≤ c/M ≤ 0.5) at 298.15 K have also been performed. At sufficient water content, a large dispersion with a relaxation time of ∼600 ps has been obsd. at ∼300 MHz and attributed to the av. reorientation of water mols. residing in the close vicinity of the polar interface of the AOT headgroup and n-heptane. The reorientation of these interfacial water mols. is probably responsible for the nanosecond component obsd. in numerous polar solvation dynamics expts. in these reverse micelles. Subsequently, the estd. polarity and the measured reorientational time scale have been used to explain the dramatic slowing down of the ICT reaction rate and its dependence on pool size in these confined environments.