AGGREGATION OF 1,12-BIS(1-PYRENYL)DODECANE IN SOL-GEL SYSTEMS

Silica sol-gel systems were doped with a low concentration of 1,12-bis (1-pyrenyl)dodecane at two pH values. Fluorescence spectra of deaerate d samples were measured at regular intervals, far beyond the gel point . At least two intramolecular pyrene dimers and two excimer-like bands (E-1 and E-2) were observed for pH 1.2. In contrast, at pH 2.5, only one pyrene dimer and the sandwich excimer E-2 were detected. Decay cur ves of degassed aged gels showed that none of the excimers has a rise time at pH 1.2, but a rise-time around 8 ns was observed at pH 2.5. Th ese results were interpreted in terms of the encapsulation of the prob e in primary silica particles, whose structure and size are pH depende nt. (C) 1997 Elsevier Science B.V.