10,10'-BIS(2-ETHYLHEXYL)-9,9'-BIANTHRYL (BOA) MOLECULE - THE FIRST FREE AROMATIC PROBE FOR THE CORE OF MICELLES

The spectroscopic properties of the recently synthesized molecule 10,1 0'-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 wat er interface of the micelle where the excited probe is trapped. The dy namics 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 pre senting an attractive well about the water interface, whereas an energ y barrier prevents the diffusion of BOA toward the interface. The heig ht of this barrier has been estimated at 7kT in CTAC1 micelles. The di ffusive nature of the red shift, is shown by its dependence on viscosi ty. In CTAC1 micelles the viscosities measured from the rotational and the translational movement of the probe have the same activation diff erent points of the micelle, either in the micellar core or at the lev el of the water interface, near the polar heads. However BOA is found to largely remain located in the micellar core.