Photochemical, photophysical, and photobiological studies of zeolite guest-host complexes

This thesis focuses on the photochemistry and photophysics of a variety of zeolite complexes, from catalysts to sunscreens. The first chapter describes the preparation and photophysical and photochemical characterization of two new photocatalytic materials. The catalysts are based on a multi-component zeolite, host-guest complex and the interaction between components was probed using time-resolved spectroscopic techniques. The catalytic efficiency, in terms of the ability to photodegrade biological contaminants, was also investigated. These studies were performed with the aim of developing efficient catalysts for wastewater remediation which can be used with solar (visible) radiation. In subsequent chapters, zeolite materials have been used as matrices for the stabilization of various transient or reactive species. In the case of ZSM-5-type zeolite, the dibenzotropylium cation was rendered indefinitely persistent allowing the examination of its excited-state behaviour. The geometric restriction within the cavities also permits the observation of electron transfer chemistry in the absence of a nucleophilic addition reaction with the electron donor. In a second example, ketoprofen (a non-steroidal anti-inflammatory drug) was found to undergo intrazeolite photodecarboxylation to generate a benzylic carbanion. The lifetime of the zeolite-encapsulated carbanion was found to be fifty times longer than in solution. The enhanced lifetime allows intermolecular nucleophilic addition chemistry to compete with protonation, effectively, a photo-initiated Grignard-type reaction is observed. In Chapter 6, fluorescence is used as tool to probe both intra- and interzeolite interactions. In the first part, a zeolite-entrapped radical probe was prepared by ship-in-a-bottle synthesis for the investigation of radical percolation in the zeolite matrix. The probe is a molecular dyad containing a persistent free-radical and a quenched fluorophore. When the probe radical couples with a carbon-centered radical, the probe fluorescence is restored and in this way free-radical species in heterogeneous systems can be conveniently examined. In the second section, zeolite particles were irreversibly labeled with a biologically-compatible fluorophore (also by ship-in-a-bottle synthesis). The last part of this thesis deals with a project relating to supramolecular sunscreens. (Abstract shortened by UMI.