title: The photoformation of a phthalide: a ketene intermediate traced by FSRS.
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.
authors.affiliation: Heinrich Heine Universität, Institut für Physikalische Chemie, Universitätsstraße 1, 40225 Düsseldorf, Germany. gilch@hhu.de.
authors.forename: Sascha
authors.initials: S
authors.lastname: Fröbel
authors.forename: Laura
authors.initials: L
authors.lastname: Buschhaus
authors.forename: Torben
authors.initials: T
authors.lastname: Villnow
authors.forename: Oliver
authors.initials: O
authors.lastname: Weingart
authors.forename: Peter
authors.initials: P
authors.lastname: Gilch
mesh_terms: D001547:Benzaldehydes / Q000737:chemistry*; D001572:Benzofurans / Q000737:chemistry*; D005030:Ethylenes / Q000737:chemistry*; D007536:Isomerism; D007659:Ketones / Q000737:chemistry*; D007783:Lactones / Q000737:chemistry; D008027:Light; D011789:Quantum Theory; D013059:Spectrum Analysis, Raman
chemical_list: D001547:Benzaldehydes; D001572:Benzofurans; D005030:Ethylenes; D007659:Ketones; D007783:Lactones; C044969:2-acetylbenzaldehyde; C082022:phthalide; C008223:ketene