Sol-gel silicate thin films bearing attached pyrene fluorescing probes hidden from oxygen but still accessible to organic electron transfer quenchers

Acid or base catalysts were used to prepare sol–gel thin films of silica (AF and BF respectively) doped with a pyrene fluorescent probe covalently attached to the silica network. The polarity of the matrix was found to change according to the catalyst used. Fluorescence quenching of the excited states of the pyrene monomer by electron donors and acceptors enabled us to evaluate the accessibility of the probing dopant. A model considering the possibility of two different dopant sites is proposed for the understanding of the fluorescence quenching data. A fraction of the fluorophore is freely accessible and may be quenched, while the rest remains unquenched due, for instance, to a too deep entrapment in the silica network. The pyrene dopant was found to be almost insensitive to oxygen quenching. A tentative explanation of this peculiar protection versus oxygen is discussed.