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 (A F and BF respectively) doped with a pyrene fluorescent probe covalently att ached to the silica network. The polarity of the matrix was found to change according to the catalyst used. Fluorescence quenching of the excited stat es of the pyrene monomer by electron donors and accepters enabled us to eva luate the accessibility of the probing dopant. A model considering the poss ibility of two different dopant sites is proposed for the understanding of the fluorescence quenching data. A fraction of the fluorophore is freely ac cessible and may be quenched, while the rest remains unquenched due, for in stance, to a too deep entrapment in the silica network. The pyrene dopant w as found to be almost insensitive to oxygen quenching. A tentative explanat ion of this peculiar protection versus oxygen is discussed. (C) 1999 Elsevi er Science S.A. All rights reserved.