Date of Award

Summer 5-2021

Level of Access Assigned by Author

Open-Access Thesis

Degree Name

Doctor of Philosophy (PhD)

Department

Chemistry

Advisor

Matthew Brichacek

Second Committee Member

Alice E. Bruce

Third Committee Member

Mitchell R. Bruce

Additional Committee Members

William Gramlich

Michael Kienzler

Abstract

Nitrogen heterocycles such as quinolines, benzothiazines, benzothiazoles, and indoles are widely found in nature and these compounds have significance in organic and medicinal chemistry, biochemistry as well as materials science. Monomeric units of eumelanin (brominated 5,6- dimethoxyindolecarboxylate derivatives) were synthesized and regioselectively functionalized to form three monobrominated, three dibrominated, and a tribrominated variant using thermally induced nitrene insertions. After deprotection, three monobrominated 5,6-dihydroxyindole carboxylate (DHICA) derivatives were synthesized, and their UV-Vis absorbance was compared to DHICA. Bominated DHICA derivatives showed similar λmax as DHICA (~330 nm) but did not show aerial oxidation as evident by absence of chromophore absorbance at 550 nm. Monomeric synthetic analogues of pheomelanin subunit benzothiazole (six variants) and benzothiazine (four variants) were synthesized with CO2Et and CH2CN sidechain via Sandmeyer reaction, and Cu (II)- catalyzed thiolation-Ullmann coupling, respectively. This monomeric pheomelanoid synthesis was the first successful unified strategy to access this class of molecules. Utilizing these melanin building blocks, synthesis of mixed melanoids was done using Miyaura borylation and Suzuki- coupling. Preliminary photophysical studies of synthesized mixed melanoids showed red shifted UV absorbance (from ~280 nm to 360 nm) due to extended conjugation and these compounds exhibited fluorescence properties as organic chromophores. With a goal of developing material for optical memory, gold-heli viologen was synthesized and characterized successfully via Pd (0)- catalyzed Stille coupling route, or Hiyama-Heck coupling from 3-bromoquionoline as the key step. Temperature variable photoluminescence and quenching experiments were performed to study the photophysical behavior which showed quenching of gold luminescence by heli-viologen involving an electron transfer.

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