Development of triplet excited state probes for organized media.
Creators: name: Boch, Ronald.
Publisher: name: Université d'Ottawa / University of Ottawa
Year: 1995
Subjects: subject: Chemistry, Physical.

description: This thesis describes the detailed evaluation of using triplet excited states of p-methoxypropiophenone derivatives to probe organized media both in the solid state and in solution. The ketone triplets decay by intramolecular charge transfer $\beta$-aryl quenching of the excited carbonyl and show a high sensitivity to conformational constraints imposed by substituents or by the surrounding environment. The experience acquired with the ketone probes proved useful also in the study of $\alpha$-terthienyl in protein environments. Preliminary experiments with chiral derivatives of these triplet ketone probes in solution, showed that methyl substitution at the $\beta$-metyhylene position (which is not a participant in the deactivation mechanism) causes a dramatic decrease in the triplet lifetime. This effect is attributed to conformational preferences imposed by the added substituents. Methyl substitution in the $\beta$-aryl ring affects the ease of oxidation of this ring and as a result induces changes in the kinetics for intramolecular charge transfer. In the solid state, X-ray structures show that the charge transfer interaction provides also an efficient mode of deactivation for the $\beta$-methylene substituted ketones but not in the unsubstituted one which crystallizes in a stretched conformation. In the case of p-methoxy-$\beta$-phenylbutyrophenone, the triplet lifetime in the solid state is 420 ns for the pure R and S enantiomers but 733 ns for the racemic crystals, showing an interesting case of chiral discrimination. Powder X-ray and solid state NMR data suggest that conformational and packing differences between the enantiomers and racemic crystals are responsible for differences in the efficiency of intramolecular deactivation. Incorporation of these probes into chiral hosts such as cyclodextrins and cholate micelles lengthen the triplet lifetimes by restricting the movement of the $\beta$-phenyl ring and thus slowing down the intramolecular deactivation process. Studies using these methyl substituted ketone probes in cyclodextrins provided information on intracavity mobility, inclusion geometries, and generally on the importance of steric factors in the formation and stability of cyclodextrin complexes. Intramolecular quenching, characteristic of these probes, provides further information on specific stereochemical constraints in CD complexes and magnifies the effects observed in homogeneous solution. Solid CD inclusion complexes were also prepared and the triplet behavior observed in the solid state was compared to solution. In anionic micelles, the ketone probes undergo two-photon photoionization under conditions of pulsed laser excitation. Both SDS and sodium cholate micelles promoted charge separation and led to hydrated electrons (e$\rm\sp-\sb{aq}$) that could be readily detected by their absorption at $\lambda &gt; 600$ nm and through its reactions with oxygen and nitrous oxide. The lifetimes of e$\sp-\rm\sb{aq}$ were determined by small concentrations of aromatic ketone in the aqueous phase in equilibrium with the micelle solubilized ketone. The triplet behavior of $\alpha$-terthienyl photosensitizers conjugated to bovine serum albumin (BSA) was investigated. The protein conjugates were to serve as models for antibody conjugates for elucidating insect resistance to pesticides. The conjugates were prepared with varying amounts of sensitizer attached to the protein. Oxygen quenching of the conjugated $\alpha$-terthienyl triplet states is approximately an order of magnitude slower in the protein environment compared to homogeneous solution. (Abstract shortened by UMI.)