10,10‘-Bis(2-ethylhexyl)-9,9‘-bianthryl (BOA) Molecule:  The First Free Aromatic Probe for the Core of Micelles

Abstract

The spectroscopic properties of the recently synthesized molecule 10,10‘-bis(2-ethylhexyl)-9,9‘-bianthryl (BOA) and of its parent molecule 9,9‘-bianthryl (BA) have been studied in micelles. A time-resolved red shift in the transient fluorescence spectra has been interpreted as a diffusion process of the excited probe from the apolar core to the water interface of the micelle where the excited probe is trapped. The dynamics of the diffusion process are governed by the chemical potential profile of the excited probe through the Smoluschowski equation. The diffusion of excited molecules of BA occurs on a potential surface presenting an attractive well about the water interface, whereas an energy barrier prevents the diffusion of BOA toward the interface. The height of this barrier has been estimated at 7 kT in CTACl micelles. The diffusive nature of the red shift is shown by its dependence on viscosity. In CTACl micelles the viscosities measured from the rotational and the translational movement of the probe have the same activation energy. Finally we have confirmed that the solubilization site of BA in its ground state is localized in different points of the micelle, either in the micellar core or at the level of the water interface, near the polar heads. However BOA is found to largely remain located in the micellar core.