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Issue 1, 2015

The photoformation of a phthalide: a ketene intermediate traced by FSRS

Author affiliations

Abstract

The photo-isomerization of o-acetylbenzaldehyde (oABA) in acetonitrile was studied by femto- and nanosecond transient absorption spectroscopy. Spectroscopic signatures are assigned with the aid of TD-DFT, TD-CAM-DFT and DFT-MRCI computations. The isomerization yields a lactone, 3-methylphthalide (3MP), with a quantum yield of 0.3 (30%). As evidenced by femtosecond stimulated Raman spectroscopy (FSRS), the isomerization proceeds via a ketene intermediate. It is formed within ∼2–3 ps after photo-excitation. Intersystem crossing (ISC) populating the triplet state of oABA seems to compete with the ketene formation. Experiments on the non-reactive meta- and para-derivatives, which undergo efficient ISC with time constants of 5 ps, support this statement. The triplet state of oABA also contributes to the ketene formation, presumably involving a biradical intermediate. The ketene exhibits a lifetime of 1.4 μs and generates an additional intermediate in the cascade towards the lactone.

Graphical abstract: The photoformation of a phthalide: a ketene intermediate traced by FSRS

Supplementary files

Article information


Submitted
28 Jul 2014
Accepted
30 Oct 2014
First published
12 Nov 2014

Phys. Chem. Chem. Phys., 2015,17, 376-386
Article type
Paper
Author version available

The photoformation of a phthalide: a ketene intermediate traced by FSRS

S. Fröbel, L. Buschhaus, T. Villnow, O. Weingart and P. Gilch, Phys. Chem. Chem. Phys., 2015, 17, 376 DOI: 10.1039/C4CP03351E

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