[Photoluminescence from bis-t-butylbenzoxazolylthiophene doped silica films].

Thin nano-porous silica films doped with high concentrations of fluorescent material, 2, 5-bis (5-tert-butyl-2-benzoxazolyl)-thiophene (BBOT) were prepared via a sol-gel process. Uniform and bright blue fluorescence was observed. Light emission properties of these organic molecule doped inorganic silica films, i.e., hybrid films, were measured using ultraviolet-visible (UV-Vis) absorption spectroscopy, steady and time-resolved fluorescence spectroscopy as well as optical microscopy. Features of these materials were revealed in this investigation: Firstly, photoluminescence intensity from BBOT doped silica films increased linearly as the concentrations of BBOT increased if the dopant concentration was relatively low and below 6 x 10(-3) mol x L(-1); Secondly, no molecular aggregation or phase separation was observed using optical microscopy when the BBOT concentration was below 6 x 10(-3) mol x L(-1) in BBOT doped silica films. Thirdly, the fluorescence lifetimes of BBOT in the doped silica films were longer than that in a dilute dioxane solution (1.957 ns), which was contradicted to our general understanding that the fluorescence lifetime may be reduced in a condensed matter due to molecular interactions or quenching. It was further found that the fluorescence lifetime also varied with the gelation conditions. Taking a BBOT concentration of 6 x 10(-3) mol x L(-1) for an example, the lifetime of BBOT in doped silica films was about 2.45 ns for a specimen polymerized at 50 degrees C; while the lifetime was increased to 3.04 ns for a specimen polymerized at 90 degrees C. This work demonstrates no concentration quenching when the BBOT dopant concentrations increased to as high as 6 x 10(-3) mol x L(-1) in the silica matrix. In comparison with the changes in time-resolved photoluminescence of BBOT in dioxane solution and that of the BBOT doped nano-porous silica in relation to their concentration dependence and the gelation conditions, it was found that concentration quenching can be effectively suppressed by the nano-porous silica matrix. A stable fluorescent organic-inorganic hybrid material is thus obtained.