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

Ranjit Biswas, Nashiour Rohman, Tuhin Pradhan and Richard Buchner,

J. Phys. Chem. B  112  (2008) 9379-9388. DOI: 10.1021/jp8023149


Abstract

Intramolecular charge transfer (ICT) reaction in a newly synthesized molecule, of 4-(1-morpho-lenyl) 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 equilibrium constant and reaction rate have been explained in terms of the average polarity of the confined solvent pools estimated 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 <=n/GHz <=2 for these microemulsions at different
pool sizes (0 <=w0<=40 and AOT concentrations (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 observed at ~300 MHz and attributed to the average reorientation of water molecules residing in the close vicinity of the polar interface of the AOT headgroup and n-heptane. The reorientation of these interfacial water molecules is probably responsible for the nanosecond component observed in numerous polar solvation dynamics experiments in these reverse micelles. Subsequently, the estimated 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.
(c) 2008 Berger Georg