Intramolecular charge transfer and reactivity of the norbornadiene cation radical: Transition states and conical intersections

Chemical transformations of the norbornadiene cation radical (NRB + • ) involving intramolecular electron transfer (IET) are analysed using a two-dimensional potential surface formed by reaction coordinates along two pathways. One leads to the quadricyclane cation radical, the other to the benzene cation radical plus a methylene biradical. Two separate conical intersections between the ground state and the first excited state of (NRB +• ) are located using the Longuet-Higgins sign-inverting theorem. The implications of this finding on the photodynamics of the system are discussed.