Nanoscale properties and matrix-dopant interactions in dye-doped organically modified silicate thin films

The nanoscale properties of organically modified sol-gel-derived silicate t hin films are studied in detail by single-molecule spectroscopic methods. F or these studies, the solvent-sensitive probe Nile Red is doped into the fi lms at nanomolar concentrations. Spectroscopic data are obtained for films prepared from sols containing different mole fractions of isobutyltrimethox ysilane, and tetraethoxysilane. The data are analyzed using a model based o n Marcus theory, providing important new information on static local film p roperties such as polarity and the extent of specific dopant-matrix interac tions. Data on dynamic phenomena related to local matrix rigidity is also o btained, In general, throughout the range of samples studied, the most pola r environments are also found to be the most rigid. With regard to their st atic properties, broad heterogeneous distributions are found in films of pr edominantly inorganic composition. In several instances, bimodal distributi ons are also observed, which result from specific chemical interactions and likely involve hydrogen bonding of the dye to the silicate matrix and/or t o entrapped solvent. As the organic content of the film is increased, the f ilm environments become less polar, less rigid, and more homogeneous. In ad dition, the effects of specific chemical interactions become dramatically l ess apparent. With respect to dynamic film properties, two distinct distrib utions are observed in films of intermediate organic/inorganic composition, reflecting the presence of environments differing in their rigidity. Studi es of time-dependent single-molecule fluorescence fluctuations provide supp ort for the conclusions derived from the spectroscopic data.