Conical Intersection in Chemiluminescence of Cyclic Peroxides.

Chemiluminescence (CL) utilizing chemiexcitation for energy transformation is one of the most highly sensitive and useful analytical techniques. The chemiexcitation is a chemical process of a ground-state reactant producing an excited-state product, in which a nonadiabatic event is facilitated by conical intersections (CIs), the specific molecular geometries where electronic states are degenerated. Cyclic peroxides, especially 1,2-dioxetane/dioxetanone derivatives, are the iconic chemiluminescent substances. In this Perspective, we concentrated on the CIs in the CL of cyclic peroxides. We first present a computational overview on the role of CIs between the ground (S 0 ) state and the lowest singlet excited (S 1 ) state in the thermolysis of cyclic peroxides. Subsequently, we discuss the role of the S 0 /S 1 CI in the CL efficiency and point out misunderstandings in some theoretical studies on the singlet chemiexcitations of cyclic peroxides. Finally, we address the challenges and future prospects in theoretically calculating S 0 /S 1 CIs and simulating the dynamics and chemiexcitation efficiency in the CL of cyclic peroxides.