Identification of Oblique and Coplanar Inclined Fluorescent J-Dimers in Rhodamine 110 Doped Sol-Gel-Glasses

Rhodamine 110 (R110) fluorescent J-dimers have been first observed in doped silica gel-glasses made by sol-gel process. The R110 doped gel-glasses photophysical properties such as excitation/fluorescence spectra and lifetimes were studied in a wide range of dye concentrations. It has been determined that the formation of R110 dimers is a consequence of the dye adsorption on the porous surface of the gel-glasses. The adsorption geometry, which is established by the angle formed between the longitudinal axis of the molecule and the gel surface, determined the formation of either R110 fluorescent J-dimers or nonfluorescent H-dimers. Since the adsorption angle was related to the dye concentration, the transition from J-dimers to H-dimers was found for a specific R110 concentration. Formation of J-dimers with a preferential oblique or coplanar inclined configuration was induced by the change of the polar character of the adsorption surface.