Four-state conical intersections: The nonradiative deactivation funnel connected to O–O homolysis in benzene endoperoxide

The radiationless decay process connected to the breaking of the O–O bridge in benzene endoperoxide has been investigated using high-level ab initio multiconfigurational MS-CASPT2//CASSCF methods. The homolytic rupture of the O–O bond is controlled by a four-state conical intersection. The nine vectors which define the branching space of this high-order degeneracy point have been extracted from two-state conical intersection calculations between the electronic states involved in the degeneracy. The existence of four-state conical intersections indicates that, in general, endoperoxides can deactivate through very efficient radiationless funnels.