Theoretical study of the dark photochemistry of 1,3-butadiene via the chemiexcitation of Dewar dioxetane

Abstract

Excited-state chemistry is usually ascribed to photo-induced processes, such as fluorescence, phosphorescence, and photochemistry, or to bio-and chemiluminescence, in which light emission is originated by a chemical reaction. A third class of excited-state chemistry, however, is possible that promotes photochemical phenomena by chemienergizing certain chemical groups without light -chemiexcitation. By studying Dewar dioxetane, which can be viewed as the combination of 1,2-dioxetane and 1,3-butadiene, we show here how the isomerization * To whom correspondence should be addressed † Uppsala ‡ València ¶ UC 3 1 channel that characterizes the photo-induced chemistry of 1,3-butadiene can be reached at a later stage after the thermal decomposition of the dioxetane moiety. Multi-reference multiconfigurational quantum chemistry methods and accurate reaction-path computational strategies were used to determine the reaction coordinate that first decomposes the dioxetane, next transfers non-adiabatically the state from the ground to the excited state, and finally brings the system into the photochemical channel of the 1,3-butadiene group. With the present study, we open a new area of research within computational photochemistry to study chemically-induced excited-state chemistry that is difficult to tackle experimentally due to the short-lived character of the species involved in the process. The findings shall be of relevance to unveil "dark" photochemistry mechanisms which might operate in biological systems in conditions of lack of light to allow reactions that are typical of photo-induced phenomena.

A combined theoretical and experimental study on the mechanism of spiro-adamantyl-1,2-dioxetanone decomposition

“…Considering the previous studies on 1,2-dioxetane, 14 1,2-dioxetanone 15 and Dewar 1,2-dioxetane, 20 one can claim that these O-O bond breaking reactions occur via a two-step mechanism for most of the cases. This, however, has been illustrated in Section 3, applying the intrinsic reaction coordinate (IRC) calculations.…”

Molecular Basis of the Chemiluminescence Mechanism of Luminol

“…For 2) a highly correlated active space of 10 electrons distributed among 8 orbitals (CAS(10,8)) was used and corresponded to all relevant valence σ, σ*, n, π, and π* orbitals (see Figures S22–S25 in the Supporting Information). Four singlet and four triplet CASSCF wave functions were averaged in such computations to take into account the possibility of distinct biradical configurations appearing, as in 1,2‐dioxetane or Dewar dioxetane . Based on the analysis of the 1,2‐dioxin small model and further tests on the LH 2 system, for 1) and 3), appropriate CAS(12,10) was chosen for geometry optimizations and CAS(18,14) for single‐point CASPT2 computations (see Figure S26–S29 in the Supporting Information).…”

“…Four singlet and four triplet CASSCF wave functions were averaged in such computations to take into account the possibility of distinct biradical configurations appearing, as in 1,2-dioxetane [1,47,74] or Dewar dioxetane. [75] Based on the analysis of the 1,2dioxin small model and further tests on the LH 2 system, for 1) and 3), appropriate CAS(12,10) was chosen for geometry optimizations and CAS (18,14) for single-point CASPT2 computations (see Figure S26-S29 in the Supporting Information). CASSCF state averaging over ad ifferent number of roots was performed according to the type of computation;four for single-point calculations and two for geometry optimizations.…”

Advances in computational photochemistry and chemiluminescence of biological and nanotechnological molecules

“…The molecular basis of this unconventional type of excited-state chemistry was established theoretically by Farahani et al 161 through the study of the thermal decomposition of Dewar dioxetane. This molecule is a combination of 1,2-dioxetane and 1,3-butadiene, which was first presented by McCapra 162 in the study of the thermal decomposition of Dewar benzene.…”

“…Thus, the Dewar dioxetane was suggested to be formed in this process and to be responsible for the luminescence. In the theoretical study by Farahani et al, 161 the CASPT2//CASSCF method was employed to characterize the PESs of the lowest-lying singlet and triplet states along the decomposition coordinates on the S 0 , S 1 and T 1 manifolds. An initial O-O bond breaking and subsequent C-C cleavage via a two-step biradical mechanism was determined as the reaction pathway for the thermal decomposition of the Dewar dioxetane.…”