Issue 14, 2015

Observation of excited state proton transfer reactions in 2-phenylphenol and 2-phenyl-1-naphthol and formation of quinone methide species

Abstract

The excited state intramolecular proton transfer (ESIPT) reactions from a phenol (naphthol) to a carbon atom in the adjacent aromatic ring of 2-phenylphenol (1) and 2-phenyl-1-naphthol (4) are prototypical examples of intramolecular proton transfer not mediated by solvent molecules. Femtosecond time-resolved transient absorption (fs-TA) studies are conducted for the first time to directly probe the formation of quinone methide (QM) species generated from the ESIPT pathways of 1 and 4. Steady-state absorption experiments demonstrated 1 exists mainly in its non-deprotonated form in neat MeCN and in water–MeCN solutions. Observation of the phenolate form in water-containing solution (MeCN–H2O, 1 : 1, v : v) in fluorescence spectra demonstrates the occurrence of an ESPT reaction between 1 and the surrounding water molecules. In neat MeCN a transient species that absorbs around 520 nm was detected in fs-TA spectra and was assigned to the QM species formed by ESIPT to the 2′-position. This transient signal is strengthened in cyclohexane. In a water–MeCN solution, an additional transient species assigned to the QM species at the 4′-position of 1 was also detected that absorbs around 485 nm. Similar results for 4 were observed, with the absorbance of the transient species being more intense, which suggests there is more efficient production of the QM species from 4, consistent with quantum yields for deuterium exchange in the distal ring reported for these compounds.

Graphical abstract: Observation of excited state proton transfer reactions in 2-phenylphenol and 2-phenyl-1-naphthol and formation of quinone methide species

Supplementary files

Article information

Article type
Paper
Submitted
03 Nov 2014
Accepted
05 Mar 2015
First published
05 Mar 2015

Phys. Chem. Chem. Phys., 2015,17, 9205-9211

Author version available

Observation of excited state proton transfer reactions in 2-phenylphenol and 2-phenyl-1-naphthol and formation of quinone methide species

J. Ma, X. Zhang, N. Basarić, P. Wan and D. L. Phillips, Phys. Chem. Chem. Phys., 2015, 17, 9205 DOI: 10.1039/C4CP05061D

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