Photochemical Sciences Ph.D. Dissertations

Manipulating Excited State Pathways to Uncover New Photochemical Processes

Date of Award

2023

Document Type

Dissertation

Degree Name

Doctor of Philosophy (Ph.D.)

Department

Photochemical Sciences

First Advisor

Jayaraman Sivaguru (Committee Chair)

Second Advisor

Lori Brusman Lovins (Committee Member)

Third Advisor

Pavel Anzenbacher Jr (Committee Member)

Fourth Advisor

Alexander Tarnovsky (Committee Member)

Abstract

Uncovering untrodden photochemical pathways often depends on manipulating reactive chromophores and channeling their excited state energy towards a desired chemical pathway. To alter an established photochemical reactivity, a clear comprehension of the dynamics of the excited states involved is quintessential. This thesis will present the development of a new class of photochemical reaction which was established by circumventing an established excited state process. We have designed chromophores in which a new type of photochemical reactivity was observed in excited 1,3-dicarbonyl compounds with activated alkene circumventing the traditional De Mayo pathway. In Chapter 2 we will discuss in detail regarding this newly observed reaction, which allows the conversion of completely planar reactants to a complex heterocyclic structure with multiple stereocenters in a single step. Photophysical investigations have enabled us to elucidate the mechanism of this new excited state process. To enhance the applicability of this newly discovered photoreaction, we have also evaluated the structural features that are crucial for controlling the excited state processes in Chapter 3. Our investigations have uncovered the role of cyclic dicarbonyl compounds in dictating the regiochemical outcome of this new photoreaction leading to the formation of complex heterocycles. By manipulating the reaction temperature in various solvents, the regioselectivity in different cyclic carbonyl compounds were evaluated allowing us to build complex heterocycles in a single step by considering the principle of green chemistry and atom economy. Based on detailed photophysical and spectroscopic studies, the mechanism for the observed difference in the regiochemistry of the photoproduct based on the ring size of the dicarbonyl compound employed for the photo transformation was uncovered. The final aspect of the thesis, Chapter 4 details a design to circumvent the known [2+2]-photodimerization in maleimides uncovering an unusual [4+2]-photodimerization reaction. The detailed mechanistic studies will be presented to rationalize this new reactivity.

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