Electronically nonadiabatic thermal reactions of organic molecules

Abstract

This critical review seeks to bring together organic reactions in which thermal generation of electronic excited states plays an important role. The best known such reactions are those producing chemiluminescent products. However, it appears that there may exist at least as many nonadiabatic reactions in which the excited molecules react before they luminesce. An effort is made to understand the efficiency of excited state production. The crucial roles played by reactive intermediates are highlighted.

Four‐membered cyclic peroxides: Carriers of chemical energy

“…Analogously, biochemical reactions can produce bioluminescence, a widespread natural phenomenon that is observed, for example, in fireflies, some species of fungi, and even sharks . Chemiexcitation occurs as the result of a nonadiabatic process where the potential energy surface of the decomposition of high‐energy species in the ground state crosses the surface of either singlet‐ or triplet‐excited products . The quantum efficiency of this process depends on several factors, the most important being the amount of energy released by the decomposition of high‐energy chemical compounds or intermediates.…”

How to Lose a Bond in Two Ways ― The Diradical/Zwitterion Dichotomy in Cycloaromatization Reactions

“…The experimental and computational data were interpreted by the authors in favor of the unusual electronically nonadiabatic reaction with post‐transition‐state bifurcation between the two alternative paths: one to the ground‐state diradical and the other to the excited‐state zwitterion 53. Thermal reactions that form products in their excited states are rare and usually include reactants that contain either strained systems54 or weak bonds,55 or both, for example, dioxetanes responsible for the bioluminescence of fireflies 56.…”

Theoretical studies on thermal stability of alkyl-substituted 1,2-dioxetanes

“…1,2 These products are formed preferentially in the electronically excited triplet state and the mechanism of this transformation was extensively studied during the 1970's and mid 1980's. 1,[3][4][5][6][7] As consequence, several hundreds of 1,2-dioxetane derivatives were synthesized.…”

“…[12][13][14] However, up to now, no definitive explanation for the chemiexcitation mechanism in 1,2-dioxetane thermolysis was obtained, neither by experimental nor theoretical means. 2,7,13,15 Most attempts on mechanistic analysis of this process focused on the question whether the O-O and C-C bond cleavage occurs concertedly or in a stepwise manner. 1,[12][13][14][16][17][18] Theoretical evidence reported so far indicates that the C-C bond stretches along the reaction coordinate, which is consistent with the intuitively assessed merged dioxetane cleavage mechanism, which predicts the concerted, although not simultaneous, cleavage of the O-O and C-C bonds, with the elongation of the O-O bond being more advanced than that of the C-C-bond (concerted biradicallike mechanism).…”