3H-INDOLES IN CETYLTRIMETHYLAMMONIUM BROMIDE (CTAB) MICELLES AND WATER - SPECTROSCOPY AND PHOTOPHYSICS AT VARIOUS TEMPERATURES

An absorption and fluorescence spectral study has been carried out for four molecules: 2-[(p-amino)phenyl]-3,3-dimethyl-3H-indole (1), 2-[(p -dimethylamino)phenyl]-3,3-dimethyl-3H-indole (2), amino)phenyl]-3,3-d imethyl-5-carboethoxy-3H-indole (3), and amino)phenyl]-3,3-dimethyl-5- carboethoxy-3H-indole (4) in cetyltrimethylammonium bromide (CTAB) and water solutions. Arrhenius plots for the nonradiative decay processes competing with fluorescence are nonlinear in CTAB. This is ascribed t o the fact that the probes are locked into a site where the twisting o f the phenyl moiety is nearly inhibited in CTAB at room temperature. T he binding constants increase in an increasing order of the molecular size (exponential growth) thereby showing that hydrophobic effects are the driving force behind the solubilization of these molecules in CTA B. Calculation of transfer free energies has confirmed the importance of the hydrophobic effect compared to the Coulombic interactions. The neutral-monocation equilibrium is lowered in presence of CTAB. (C) 199 6 Academic Press, Inc.