The DDCI Method Applied to Reactivity:  Chemiluminescent Decomposition of Dioxetane

Abstract

This paper describes how the DDCI method can be applied to study the reactivity of dioxetane, a molecule that decomposes thermally into 2 formaldehyde molecules. One of these molecules is in an excited state that decays radiatively. Previous experimental and theoretical studies proposed that this decomposition takes place through a stepwise mechanism, but the relative energies of the two transition states involved in the reaction have been a source of controversy. While experimental evidence shows that the first transition state is higher in energy, one of the latest and most accurate theoretical studies does not produce the same results. In this paper the projection of the reaction path over the ground-state potential energy surface (PES) is calculated with a conventional method. We calculate the energies of the species on the excited states involved in the reaction by adding the energy of the vertical transition to the ground-state energies. To do so we use the DDCI method, which was specifically designed to calculate energy differences. The first transition state, located in the ground-state PES, is found to be higher in energy than the second one, located in the T 1 PES. This result agreed with the experimental result.

Mechanistic insights into the efficient intramolecular chemiexcitation of dioxetanones from TD‐DFT and multireference calculations

“…Our focus in this study is to determine the mechanism that allows the presence of this region of degeneracy and controls its length, and thereby determine the reason behind efficient chemiexcitation. It should be noted that some authors have proposed a mechanism for explaining the zone of degeneracy: as the peroxide bond breaks, the σ and σ* orbitals become O lone pairs, almost degenerate with the original O lone pairs (initially perpendicular to the ring plane) . However, we do not think it to be a satisfactory explanation for this process.…”

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

“…Since the semiempirical PM3 and AM1 methods do not adequately describe dihedral angles for bisadamantylidene-1,2-dioxetane (30), it is questionable if they are able to accurately predict ω for less stable derivatives, e.g., parent 1,2-dioxetane or tetramethyldioxetane. In this context, it should be considered that AM1 and PM3 methods are both based on the Neglect of Differential Diatomic Overlap (NDDO) integral approximation, but with an automatic parameterization procedure for PM3.…”

“…However, X-ray structural data of these simpler derivatives are not available and theoretical bond distances, angles and dihedral angles are very often compared with that of much more stable 1,2-dioxetanes (see Table S4). [12][13][14]16,17,30 In other words, there are no experimental data concerning the structure of less stable 1,2-dioxetanes and, therefore, it is impossible to assign unequivocally the more adequate theoretical method to access the optimized geometry. In order to adequately compare structural parameters predicted by different methods with experimental values, the geometry of the derivative 30 was optimized by AM1, PM3, HF/6-31G(d) and B3LYP/6-31G(d) methods and the results evaluated with that obtained by X-ray diffraction (Table 3).…”

Methods for describing open-shell systems: Following the trail of Rosa Caballol's research

“…Although the study of the magnetic coupling has long been (and probably still is) the major area of application, DDCI has also been used to study vertical excitations spectra, [64,65] ionization energies, and weakly avoided crossings, [66] potential energy surfaces in photochemistry, [67,68] relative stability of different biomimetic adducts, [54] hopping probabilities in doped systems or mixed valence compounds, [69][70][71][72] conduction properties of 1D organic chains, [73,74] and the electronic structure of systems with magnetoresistance effects, [75][76][77] among others.…”