Photochemical Sciences Ph.D. Dissertations

Uncovering New Photochemical Pathways Through Molecular Restrictions

Date of Award

2020

Document Type

Dissertation

Degree Name

Doctor of Philosophy (Ph.D.)

Department

Photochemical Sciences

First Advisor

Jayaraman Sivaguru (Advisor)

Second Advisor

Anne K. Gordon (Other)

Third Advisor

Malcolm D.E. Forbes (Committee Member)

Fourth Advisor

Alexis Ostrowski (Committee Member)

Abstract

Light is a sustainable and benign source of energy and its prevalent in nature. Chemical processes that require light are known as photochemical process. Origin of life on earth is potentially be related to the chemical effect of light with sun being the central figure. Photosynthesis and synthesis of vitamin D are the simplest examples of photochemical processes that are crucial in nature. Inspired by the nature, scientists strive to replicate the potential of photochemical processes in designing and synthesizing complex organic molecules in organic photochemistry. Often times, photochemical reactions can open new reaction pathways of certain organic molecules due to dynamic nature and time frame of the excited states involved in the particular photochemical reaction. This requires a thorough mechanistic understanding of excited state characteristics of organic molecules. Inherently, light initiated processes are extremely fast that leaves a little room to manipulate the reactivity and selectivity of molecules in a photochemical reaction. Additionally, the barrierless nature of photochemical reactions contributes to the low selectivity in contrast to its thermal counterpart that is an uphill process requiring an activation energy to overcome reaction barrier. This dissertation details the strategies to control the selectivity and manipulating the excited state reactivity to open new reaction pathways in photochemical reactions.

First chapter describes the fundamentals concepts of excited state nature and processes with an overview of basic organic photochemical reactions of molecules. A brief history of various approaches to control selectivity in photochemical reactions is discussed. In the later part of chapter, an approach based on atropisomers which has been utilized in this dissertation in investigating the photochemical reactions is detailed.

Second chapter details the use of atropisomers in attaining regio- and atrop-selectivity in [2+2]-photocycloaddition reaction of maleimide chromophore along with complete mechanistic study using photophysical experiments.

Third chapter of explores new photochemical reactivity of maleimide chromophore towards photo-ene reaction along with mechanistic investigations.

Fourth chapter deals with a photo-auxiliary approach to control regioselectivity of oxazolidinone based hydrazides. It also describes light mediated thiol addition of phthalimide based hydrazides.

Fifth chapter describes Diels-Alder reaction of maleimide chromophore under photochemical conditions.

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