title: The photochemical ring opening reaction of chromene as seen by transient absorption and fluorescence spectroscopy.
abstract: In this paper we investigate the photochromic ring-opening reaction of 2,2-diphenyl-5,6-benzo(2H)chromene. In particular, we study the uncertainties and contradictions in various published reaction models using a combination of transient absorption and fluorescence spectroscopy with femtosecond time resolution. We propose a simplified reaction scheme which is in good agreement with theoretical studies. Here, photoexcitation populates a Franck-Condon state, whose fast vibrational wave packet motion, vibrational relaxation, bond-alternation and/or solvent rearrangement processes occur on the sub-picosecond timescale. Our data suggest that the resulting excited state minimum with picosecond lifetime still features structural characteristics of the closed form. Subsequently, the ring-opened photoproducts are formed in a concerted step from the excited state. The velocity of the photoreaction hence only depends on the time that the molecule needs to reach the transition region between the ground and excited states where the crucial bond breakage occurs.
authors.affiliation: Chair for Biomolecular Optics, Faculty of Physics, Ludwig-Maximilians-Universität München, Oettingenstr. 67, D-80538 München, Germany.
authors.forename: Teja T
authors.initials: TT
authors.lastname: Herzog
authors.forename: Gerald
authors.initials: G
authors.lastname: Ryseck
authors.forename: Evelyn
authors.initials: E
authors.lastname: Ploetz
authors.forename: Thorben
authors.initials: T
authors.lastname: Cordes
mesh_terms: D001578:Benzopyrans / Q000737:chemistry*; D008958:Models, Molecular; D011789:Quantum Theory; D012997:Solvents / Q000737:chemistry; D013050:Spectrometry, Fluorescence; D013237:Stereoisomerism; D013997:Time Factors; D014466:Ultraviolet Rays
chemical_list: D001578:Benzopyrans; D012997:Solvents