Fluorescent Probes as Reporters on the Local Structure and Dynamics in Sol−Gel-Derived Nanocomposite Materials

The use of steady-state and time-resolved fluorescence spectroscopy to probe the internal microenvironment of sol−gel-derived organic−inorganic nanocomposites formed from alkoxysilane precursors is reviewed. The review focuses on the use of small organic probes and fluorescent biomolecules that provide information on pore−solvent composition and polarity, internal solvent and dopant dynamics, environmental heterogeneity and phase segregation, and surface chemistry, as determined by molecule−matrix interactions. Emphasis is placed on advanced fluorescence methods that can provide unique information on sol−gel-derived composite materials. The discussion begins with a description of the different fluorescent probes that have been used to study sol−gel materials. The application of fluorescence methods to examine Class I and Class II hybrid materials is then described, highlighting the specific information available from different probes and the methods used to obtain information on the structure and dynamics of such materials. This section highlights the overall effects of dispersed and bound organic dopants on the polarity, dynamics, heterogeneity, and surface chemistry of nanocomposites. Finally, fluorescence studies on emerging materials, including templated nanocomposites and biomaterials, are described, and the overall utility of fluorescence spectroscopy for probing of such materials is discussed.