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On the Condensed Phase Ring-Closure of Vinylheptafulvalene and Ring-Opening of Gaseous Dihydroazulene

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journal contribution
posted on 25.04.2013, 00:00 by Oliver Schalk, Søren L. Broman, Michael Å. Petersen, Dmitry V. Khakhulin, Rasmus Y. Brogaard, Mogens Brøndsted Nielsen, Andrey E. Boguslavskiy, Albert Stolow, Theis I. Sølling
Dihydroazulenes are interesting because of their photoswitching behavior. While the ring-opening to vinylheptafulvalene (VHF) is light induced, the back reaction is known to proceed thermally. In the present paper, we show the first gas phase study of the ring-opening reaction of 2-phenyl-1,8a-dihydroazulene-1,1-dicarbonitrile (Ph-DHA) by means of time-resolved photoelectron spectroscopy which permits us to follow the ring-opening process. Moreover, we investigated s-trans-Ph-VHF in a series of transient absorption experiments, supported by ab initio computations, to understand the origin of the absence of light-induced ring-closure. The transient absorption results show a biexponential decay governed by a hitherto unknown state. This state is accessed within 1–2 ps and return to the ground state is probably driven through a cis–trans isomerization about the exocyclic C1C2 double bond. The rapid decrease in potential energy disfavors internal rotation to s-cis-Ph-VHF, the structure that would precede the ring-closure reaction.