Spectroscopic studies of molecules in sol-gel silica monoliths and thin films

Abstract This article about sol-gel research in North America is focused on transparent sol-gel silica monoliths and nano-structured thin films containing encapsulated molecules. The research was a collaborative effort carried out at the University of California Los Angeles (UCLA). Our research was focused on two goals: using optical spectroscopy to understand the chemical and physical changes occurring during the sol to the xerogel transformation; and using spectroscopy to understand what was happening to the molecules themselves after encapsulation. The first section is a brief discussion of molecular probes used to monitor in real time the hydrolysis, condensation, gelation and drying of tetraethoxysilane (TEOS) formed in optical cuvettes. In the second section, we introduce dip coating of one hundred nanometer thin films and methods for measuring thickness and chemical changes in real time during film pulling. We include surfactant templated mesostructured films and real time observation of the structure development. Third, we design molecules to add to the initial sol such that they are placed in specific regions of the ordered structure of the templated film. We describe spectroscopic methods that prove their placement and use pairs of molecules for physical studies including intermolecular energy transfer. Finally, we describe “gentle” synthesis methods for encapsulating enzymes and other proteins that retain their optical and enzymatic properties. Spectroscopy provided quantitative information about the sol-gel processes, enzymatic activity, and optical sensor applications. Graphical Abstract