Excited state intramolecular proton transfer reactions in polyaryl bisphenols
LE3 .A278 2019
2019
Lukeman, Matthew
Acadia University
Bachelor of Science
Honours
Chemistry
Electronic excitation of phenols can produce a significant increase in acidity, causing the phenolic proton to transfer to basic sites on the same molecule in a reaction called an excited state intramolecular proton transfer (ESIPT). This work involves the investigation of the photochemistry of polyaryls containing two hydroxyl groups. 1,4-di(o-hydroxyphenyl)naphthalene (29) and 2-phenylresorcinol (31) were prepared using a methodology involving Suzuki coupling and demethylation, and were obtained in crude yields of 65% and 59%, respectively. Photochemical studies, including UV-Vis spectroscopy, product studies, and fluorescence spectroscopy, were performed on bisphenols p-di(o-hydroxyphenyl)benzene (28), 29, and 31. Phenol28 underwent ESIPT and reverse proton transfer (RPT) inefficiently (Φ< .01), as indicated by deuterium incorporation on the central aromatic ring.In addition, a competing side reaction was observed which gave unidentified products. ESIPT and electrocyclicring closure (ERC) took place on irradiation of 29, and the reaction proceeded cleanly with no side products. The cyclized photoproduct appeared to undergo aromatization on exposure to air. Phenol 31 underwent ESIPT and RPT which gave efficient deuterium incorporation (Φ= 0.25) at the 2’-position. The results suggest that placement of two electron-donating phenolic hydroxyl groups on the same ‘donor’ ring leads to an enhancement of ESIPT reaction efficiency, whereas placement of these two hydroxyl groups opposite to one another on different rings leads to reduced ESIPT efficiency. This is consistent with a reaction mechanism that involves substantial excited state charge transfer prior to the proton transfer step.
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https://scholar.acadiau.ca/islandora/object/theses:3249
