title: Mechanism of efficient firefly bioluminescence via adiabatic transition state and seam of sloped conical intersection.
abstract: Firefly emission is a well-known efficient bioluminescence. However, the mystery of the efficient thermal generation of electronic excited states in firefly still remains unsolved, particularly at the atomic and molecular levels. We performed SA-CASSCF(12,12)/6-31G* and CASPT2(12,12)/6-31G*//SA-CASSCF(12,12)/6-31G* calculations to elucidate the reaction mechanism of bioluminescence from the firefly dioxetanone in the gas phase. Adiabatic transition state (TS) for the O-O bond cleavage and the minimum energy conical intersection (MECI) were located and characterized. The unique topology of MECI featuring a seam of a sloped conical intersection for the firefly dioxetanone, which was uncovered for the first time, emerges along the reaction pathway to provide a widely extended channel to diabatically access the excited-state from the ground state.
authors.affiliation: Fukui Institute for Fundamental Chemistry, Kyoto University, Kyoto 606-8103, Japan.
authors.forename: Lung Wa
authors.initials: LW
authors.lastname: Chung
authors.forename: Shigehiko
authors.initials: S
authors.lastname: Hayashi
authors.forename: Marcus
authors.initials: M
authors.lastname: Lundberg
authors.forename: Toru
authors.initials: T
authors.lastname: Nakatsu
authors.forename: Hiroaki
authors.initials: H
authors.lastname: Kato
authors.forename: Keiji
authors.initials: K
authors.lastname: Morokuma