title: Femtosecond study on the isomerization dynamics of NK88. II. Excited-state dynamics.
abstract: The molecule 3,3(')-diethyl-2,2(')-thiacyanine isomerizes after irradiation with light of the proper wavelength. After excitation, it undergoes a transition, in which one or more conical intersections are involved, back to the ground state to form different product photoisomers. The dynamics before and directly after the transition back to the ground state is investigated by transient absorption spectroscopy in a wavelength region of 360-950 nm, as well as by fluorescence upconversion. It is shown that the excited-state dynamics are governed by two time scales: a short one with a decay time of less than 2 ps and a long one with about 9 ps. A thorough comparison of the experimental results with those of configuration interaction singles and time-dependent density functional theory calculations suggests that these dynamics are related to two competing pathways differing in the molecular twisting on the excited surface after photoexcitation. From the experimental point of view this picture arises taking into account the time scales for ground-state bleach, excited-state absorption, stimulated emission, fluorescence, and assumed hot ground-state absorption both in the solvent methanol and ethylene glycol.
authors.affiliation: Physikalisches Institut, Universität Würzburg, Am Hubland, D-97074 Würzburg, Germany.
authors.forename: Gerhard
authors.initials: G
authors.lastname: Vogt
authors.forename: Patrick
authors.initials: P
authors.lastname: Nuernberger
authors.forename: Gustav
authors.initials: G
authors.lastname: Gerber
authors.forename: Roberto
authors.initials: R
authors.lastname: Improta
authors.forename: Fabrizio
authors.initials: F
authors.lastname: Santoro
mesh_terms: D000042:Absorption; D016880:Anisotropy; D002232:Carbocyanines; D003596:Cytosine / Q000031:analogs & derivatives* / Q000737:chemistry; D019855:Ethylene Glycol / Q000737:chemistry; D007834:Lasers; D008027:Light; D000432:Methanol / Q000737:chemistry; D008958:Models, Molecular; D008968:Molecular Conformation; D010777:Photochemistry / Q000379:methods*; D012984:Software; D013053:Spectrophotometry; D013696:Temperature; D013816:Thermodynamics; D013997:Time Factors
chemical_list: C521847:3,3'-diethyl-2,2'-thiacyanine; D002232:Carbocyanines; C080206:5-fluoro-2-thiocytosine; D003596:Cytosine; D019855:Ethylene Glycol; D000432:Methanol