"On the Condensed Phase Ring-Closure of Vinylheptafulvalene and
Ring-Opening of Gaseous Dihydroazulene"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
J. Phys. Chem. A 2013, 117, 3340−3347
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 1,1-dicyano-2-phenyl-1,8a-dihydroazulene (Ph-DHA) by means of time-resolved photoelectron spectroscopy where
we can trace every reaction step of the ring opening process. Moreover, we investigated s-trans Ph-VHF in a series of transient absorption experiments backed 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 undisclosed 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 loss in potential energy disfavors internal rotation to s-cis Ph-VHF which would have to precede the ring closing reaction.
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