Theoretical Studies of Decomposition Reactions of Dioxetane, Dioxetanone, and Related Species. CT Induced Luminescence Mechanism Revisited

Abstract

The electronic structures and relative stabilities of homopolar biradicals (BR) and CT BR with significant one-electron transfer (ET) BR characters were investigated by ab initio MO calculations. The previously presented inter- and intra-molecular CT models were extended in order to elucidate possible mechanisms for decomposition reactions of dioxetane, dioxetanone, and related species. The computational results indicate that endothermic O–O cleavages, followed by charge-transfers, are operative for the chemiluminescence reactions of these peroxides with several anionic species, in contradiction to the chemically initiated electron-exchange luminescence (CIEEL) mechanism, where complete one-electron transfer (ET) is required for the formation of excited carbonyl fragments. The ionization potentials of monoanions of phenol, indole and luciferins were calculated semiempirically in order to estimate the CT excitation energies from these species to the O–O antibonding orbital. The CT excitation energies are used to distinguish between the CT induced luminescence (CTIL) mechanism and the CIEEL mechanism for chemiluminescence reactions. Orbital-interaction models are also presented to explain of the so-called odd/even selection rule for the efficiency of chemiluminescence reactions. The implications of these results are discussed in relation to recent experimental results, together with biological chemiluminescence reactions of luciferins and related species.

Molecular Basis of the Chemiluminescence Mechanism of Luminol

“…This scenario corresponds to the drawings based on Walsh diagrams (Figure ) and differ from the findings obtained in 1,2‐dioxin (Figure S7 in the Supporting Information), which could be attributed to the fact that in CP 2 − the π CP σ* state is stabilized by electron donation from the aniline moiety, which then produces two regions of crossing rather than one in 1,2‐dioxin. The involvement of intramolecular electron or charge transfer towards the peroxide bond in the chemiexcitation mechanism in not new, and constitutes the first step of the “chemically initiated electron‐exchange luminescence” (CIEEL) and “charge‐transfer‐induced luminescence” (CTIL) mechanisms, which have been proposed as general catalyzed chemiluminescence mechanisms in peroxide‐based systems. Intramolecular electron or charge transfer has been proposed to operate in various 1,2‐dioxetane systems containing phenolate or acridinium substituents .…”

“…On the other hand, CASPT2 MEP computations from (σ* 2 /π CP σ*) CI give rise to an evolution toward the equilibrium structure of the π CP σ* state, denoted as (π CP σ*) min , with a relative energy of −2.45 eV and an OO bond length of 2.140 Å (Figure and Figure S16 in the Supporting Information). Relative to (π CP 2 ) min , (π CP σ*) min has a higher net charge in the carboxylate groups ( δ =−1.8), which is the consequence of electron promotion from the aniline ring to the peroxide bond (see Tables S2 and S3 in the Supporting Information); a process reminiscent of intramolecular electron transfer that characterizes the CIEEL or CTIL mechanisms . Focusing on the nomenclature of the product ( 3AP 2 − ) orbitals, this state can also be referred to as a n O + π 3AP * electronic transition (see Figure S11 in the Supporting Information).…”

Hybrid density functional study of ligand coordination effects on the magnetic couplings and the dioxygen binding of the models of hemocyanin

“…Such the difference in the CT energy between from the A‐type d xy + d xy orbital to the π orbital and from the S‐type d xy − d xy orbital to the π orbital; E CT (A) < E CT (S), leads to the double charge transfer mechanism in the dioxygen binding of Hc. The CT excitation energies become smaller in these complexes as illustrated in Figure 10(B), indicating the strong configuration mixing 72. The strong CT interactions between 1b ( 1c ) and dioxygen are ascribed to the origin of the larger binding energy than that between 1a and dioxygen [Fig.…”

“…Applications of the AP scheme to the LS state have attracted recent interest in relation to biologically important binuclear transition metal complexes involved in enzymes 73. Since the J ab values for these complexes have been determined experimentally, the AP‐DFT calculations can be used for examination of reliabilities of the DFT solutions for searching the transition structures of enzyme reactions 72, 73. The chemical indices are useful for elucidation of the nature of chemical bonds based on the BS DFT calculation.…”

Luz: um raro produto de reação

“…[16][17][18][19]22,34,35,[48][49][50][51] Além disso, a maioria dos cálculos semiempíricos e ab initio foram realizados tendo o mecanismo birradicalar como base. [52][53][54][55][56][57][58][59][60] Logo, mesmo que a maioria dos cálculos reportados tenha sucesso em explicar os parâmetros de ativação da decomposição de 1,2-dioxetanos, até onde se sabe, nenhum mecanismo geral definitivo foi proposto para racionalizar os valores observados de rendimentos quânticos. 46,61 Recentemente, nosso grupo de pesquisa efetuou cálcu-los teóricos da estrutura de trinta derivados de 4 contendo substituintes alquila, otimizando-se a estrutura dos mesmos por diferentes métodos semiempíricos e ab initio.…”