LE3 .A278 2022

2022

Lukeman, Matthew

Acadia University

Bachelor of Science

Honours

Chemistry

Chemistry

The presence of a bulky substituent in the 6-position of a phenol has been shown to increase the efficiency of excited state intramolecular proton transfer (ESIPT) reactions, in which the increased acidity of the excited phenol results in a proton transfer from the hydroxyl group to a basic site on the same molecule. In this research project, we tested the generality of this idea in another system by adding a t-butyl group to the 6-position of 2-(1-naphthyl)phenol (16). Compounds 16 and 6-t-butyl-2-(1-naphthyl)phenol (25) were prepared by a Suzuki coupling reaction followed by demethylation with BBr3, giving overall yields of 68% and 67%, respectively. Both were investigated using UV-Vis spectroscopy, product studies, mass spectrometry (MS) and fluorescence. MS and UV-Vis spectroscopy were used to estimate quantum yields. Compound 25 successfully underwent ESIPT to the 2’-position and 7’-position followed by reverse proton transfer (RPT) and electrocyclic ring closure, respectively, with approximate quantum yields of ΦD = 0.28 and Φcyc = 0.025, giving Φtotal = 0.305. The overall ESIPT efficiency was similar for 16 and 25, however the relative efficiencies for ESIPT to the 2’- and 7’-positions were very different between the two compounds. The addition of the t-butyl group caused the efficiency of ESIPT to the 2’-position to approximately double, while the efficiency of ESIPT to the 7’-position decreased by a factor of 8. Fluorescence spectroscopy was used to gain insight into the S1 state of 25, and a mechanistic proposal to account for our observations is presented.

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https://scholar.acadiau.ca/islandora/object/theses:3780