PHOTOINDUCED ELECTRON TRANSFER FOR PROTECTING GROUPS AND POLYMER SYNTHESIS

Abstract

Using light to drive chemical reactions affords spatial and temporal control not typically displayed in thermal chemistry. For this reason, light induced transformations have been used in the manufacturing of polymers and plastics, and in the development of systems that require precise activation, such as drug delivery. The work presented in this dissertation will involve photoinduced electron transfer (PET) and its applications in protecting groups and polymer synthesis. Chapter 1 will discuss photoinduced electron transfer and its theory. Examples will be provided to demonstrate how it has been used as a trigger in photoremovable protecting groups, and as the mechanism of initiation in controlled radical polymerization. In Chapter 2, three different protecting groups triggered by PET will be analyzed. The analysis of key intermediates involved in the mechanism will be performed using nanosecond transient absorption spectroscopy. Chapter 3 will discuss the adaptation of an N-alkyl picoloinum protecting group to be activated by stepwise absorption of two photons of visible light. Chapter 4 will explore the photophysical properties of commonly used chain transfer agents for controlled radical polymerization. The behavior of the chain transfer agents under ultra violet and visible light photolysis, electron transfer, and energy transfer will be examined. Chapter 5 will discuss the role of the oxidation of dimethyl sulfoxide (DMSO) in the initiation of polymerization using photoredox catalysts. Our work demonstrates that, under highly oxidative conditions, an electron can be abstracted from DMSO and the resulting DMSO cation radical can degrade to for radicals capable of initiating polymerization. We explore this process for an anthraquinone-base photoredox catalyst, and apply it, along with a chain transfer agent, to the manufacturing of polymers with precise molecular weights and narrow molecular weight distributions