Probing the Microenvironment of Polymer-Impregnated Composite Glass Using Solvatochromic Dye

Poly(methyl methacrylate) (PMMA)-impregnated silica composite glasses are hosts for organics in advanced optics applications. The advantages of composite glasses are their high optical quality and mechanical strength. Composite glasses are composed of a silica skeleton which contains narrow channels. Organic polymeric chains such as longitudinal PMMA chains fill these channels to form an inorganic:organic composite glass. Using 6-propionyl-2-(dimethylamino)naphthalene (PRODAN), a solvent-sensitive dye, we probed the local microenvironment in these PMMA/silica composite glasses using steady-state and time-resolved fluorescence. The steady-state fluorescence results clearly demonstrate that the Stokes shifts (∆v) obtained for PRODAN in solid matrices (composite glass, pure PMMA, and pure silica-gel glass) are in good agreement with the expected dependence in orientational polarizability (∆f) obtained for liquid solvents. These results also demonstrate that the dye molecules are primarily surrounded by a PMMA-like environment, but there is a distinct influence of the silica skeleton and the hydrogen bonds which connect the silica matrix and PMMA. The time-resolved fluorescence results also suggest a multidomain microenvironment for the PRODAN molecules within the composite glass.