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 deaerated samples were measured at regular intervals, far beyond the gel point. At least two intramolecular pyrene dimers and two excimer-like bands (E1 and E2) were observed for pH 1.2. In contrast, at pH 2., only one pyrene dimer and the sandwich excimer E2 were detected. Decay curves 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. These results were interpreted in terms of the encapsulation of the probe in primary silica particles, whose structure and size are pH dependent.