NIR Studies of the Interactions of Decatungstate Triplet with Various Organic Molecules

Abstract

The work presented in this thesis was carried out at the Department of Chemistry & Biomolecular Sciences, University of Ottawa, Canada. It primarily addresses the hitherto unexplored photochemistry of decatungstate (DT) using a laser-based time-resolved techniques. As a member of the polyoxometalate family, the DT anion has attracted a lot of attention for the purpose of photocatalytic C-H functionalization. This is due to its remarkable photochemical activity, which holds great promise for future applications in photochemistry. Firstly, based on the extensive literature survey, a basic introduction to photochemistry related to DT, hydrogen atom abstraction reaction, and the role of DT in photocatalysis is provided. Details of the experimental techniques and instruments involved in the research work are also given. A detailed investigation characterizing the triplet state of decatungstate with a laser-based technique by studying the near-infrared emission is presented. The discovery of near-infrared (NIR) phosphorescence with a lifetime of around 100 ns, from the transient described as wO allows its unequivocal identification as the triplet state of DT in acetonitrile. Quenching of triplet DT with various hydrogen donors is also studied, and the rates are determined, allowing an understanding of the role of DT as a catalyst. Our results explain hitherto unclear phenomena, i.e., the absence of oxygen quenching of decatungstate triplet (³DT*). Further, to understand the role of DT as a photocatalyst, the quenching behaviour of the first excited triplet state of decatungstate (DT) using various peroxides, namely cumene hydroperoxide, tert-butyl hydroperoxide, and hydrogen peroxide, is examined and compared.