ADSORPTION AND EXCIMER FORMATION OF 4-(1-PYRENYL)-BUTYLTRIMETHYLAMMONIUM BROMIDE ON NONPOROUS SILICA NANOPARTICLES IN AQUEOUS DISPERSIONS

Adsorption and excimer formation of 4-(1-pyrenyl)-butyltrimethylammoni um bromide (PyB) on non-porous silica nanoparticles (Aerosil) have bee n studied in aqueous dispersions. The efficiency of excimer formation is remarkably enhanced on going from the homogeneous aqueous solution to the silica dispersion. This is ascribed to the effective adsorption of PyB onto the silica surfaces. Adsorption isotherm data are not fit ted to a simple Langmuir binding model, suggesting cluster formation o f PyB molecules on the silica surfaces. From the dependence of PyB exc imer fluorescence intensity on the surface density of the probe on the silica surface, it is elucidated that PyB molecules are inhomogeneous ly distributed on the surfaces. Excitation spectra and fluorescence de cay curves reveal that the excimers of PyB on Aerosil surfaces are mai nly originated from ground-state dimers, i.e. dynamic processes throug h lateral diffusion of the probe on the surface are less important in the present case. (C) 1998 Elsevier Science B.V. All rights reserved.