Delayed Ring-Opening in 1,3-Cyclohexadiene upon Photoexcitation to a Higher State Probed by Time-Resolved Soft X-Ray Absorption

Photo-stimulated ring-opening reaction of 1,3-cyclohexadiene (CHD) to 1,3,5-hexatriene (HT) is a pericyclic reaction and its dynamics has been investigated by various spectroscopic techniques and by theoretical approaches. Upon excitation to the 1B state, the molecular structure is distorted, and the electronic state is changed into the 2A state, of which potential energy surface has a conical intersection with that of the 1A ground state of CHD. At the conical intersection, the electronic state bifurcates toward CHD and the ring-opened HT. HT is formed on the order of a few hundred femtoseconds. [1]