Zeolite-supported tetramethyl-1,2-dioxetane: new pathways to chemiluminescence

The thermal decomposition of tetramethyl-1,2-dioxetane (TMD) sorbed into zeolite Y containing Eu³⁺ ions and 2,2'-bipyridine (samples abbreviated as ZYEBT) has been investigated. Decomposition of TMD yields, by energy transfer processes, chemiluminescence (CL) characteristic of the Eu³⁺ ion. At loading levels corresponding to an upper-limit average of 0.5, 1.0, and 2.0 TMD molecules per unit cell, the CL decay curves are nonexponential at short times; at longer times,roughly exponential curves are characterized by a unimolecular rate constant k. Analyses of the longtime decays based on an Arrhenius expression for the rate constant provide evidence for a kinetic compensation effect : plots of log k vs. the activation energy E_a as a function of TMD loading level are linear. Solution data (benzene, benzonitrile) fall on the same line, suggesting that TMD decomposes by a common rate-limiting mechanism in these various environments. The Arrhenius parameters (E_a and the pre-exponential factor A) are smaller than the solution values and increase with TMD loading. When TMD is sorbed to the extent of an upper-limit average of ~7 molecules per unit cell, CL decay curves are initially nearly flat and then show an increase in decomposition rate with time. Mechanistic implications of these results are discussed.     

Electron exchange chemiluminescence from a sterically stabilized cyclobutadiene-1,2-dioxetane

The rather stable 1,2-dioxetanes ($\text{2}$) and ($\text{3}$), derived from the sterically stabilized cyclobutadiene ($\text{1}$), exhibit distinct enhanced chemiluminescence behavior, namely energy transfer chemiluminescence (ETC) for ($\text{2}$) and electron exchange chemiluminescence (EEC) for ($\text{3}$).     

An intramolecular charge/electron transfer chemiluminescence mechanism of oxidophenyl-substituted 1,2-dioxetane

The chemiluminescence (CL) mechanism of oxidophenyl-substituted 1,2-dioxetane was investigated by performing TD-DFT calculations on biradicals of three model compounds. We propose a novel mechanism of CL in which excitation of a dissociative intermediate by infrared radiation (IRE) of the surrounding solvent is considered. The excitation energies and oscillator strengths (f-values) were estimated for intermediates along the reaction coordinate (Rx). The difference in efficiencies of CL between syn- and anti-isomers of m-oxidophenyl-dioxetane is explained using the difference in potential curves of the singlet excited states (S) and the IRE mechanism. At the point where the biradical of the anti-isomer decomposes into two fragments, the interaction between the S and triplet (T) states is induced by a significant back electron transfer (BET) from the dioxetane group to the oxido-phenyl group and the S(1) excited state is stabilized and CL efficiency is enhanced. In the syn-isomer, the barrier in the S(1) potential curve to reach the final CL state is higher than for the anti-isomer, which reduces the efficiency. The poor CL yield for the p-isomer is ascribed to a much higher barrier in the potential curve of the S(1) state.     

Reaction of tetramethyl-1,2-dioxetane with triphenylphosphine: Activation parameters for the formation of 2,2-dihydro-4,4,5,5-tetramethyl-2,2,2-triphenyl-1,3,2-dioxaphospholane

The reaction of tetramethyl-1,2-dioxetane ( 1 ) and triphenylphosphine ( 2 ) in benzene-d₆ produced 2,2-dihydro-4,4,5,5-tetramethyl-2,2,2-triphenyl-1,3,2-dioxaphospholane ( 3 ) in ?90% yield over the temperature range of 6–60°. Pinacolone and triphenylphosphine oxide ( 4 ) were the major side products [additionally acetone (from thermolysis of 1 ) and tetramethyloxirane ( 5 ) were noted at the higher temperatures]. Thermal decomposition of 3 produced only 4 and 5 . Kinetic studies were carried out by the chemiluminescence method. The rate of phosphorane was found to be first order with respect to each reagent. The activation parameters for the reaction of 1 and 2 were: Ea ? 9.8 ± 0.6 kcal/mole; ΔS^≠ = ?28 eu; k_30° = 1.8 m^?1sec^?1 (range = 10–60°). Preliminary results for the reaction of 1 and tris (p-chlorophenyl)phosphine were: Ea ? 11 kcal/mole, ΔS^≠ = ?24 eu, k_30° = 1.3 M^?1sec^?1 while those for the reaction of 1 and tris(p-anisyl)phosphine were: Ea ? 8.6 kcal/mole, ΔS^≠ = ?29 eu, k_30° = 4.9 M^?1 sec^?1.     

Mechanically induced chemiluminescence in the dispiro(adamantane-1,2-dioxetane)—Eu(fod)3 system

Luminescence accompanying an impact mechanical treatment of solid particles of the complex of Eu(fod)₃ (fod is 1,1,1,2,2,3,3-heptafluoro-7,7-dimethyloctane-4,6-dione) with dispiro(adamantane-1,2-dioxetane) (1) was discovered and studied. The luminescence has a complex structure, and its spectrum belongs to the excited Eu^III ions. The emission of light is observed only in a mechanical mixture of the Eu(fod)₃ with dioxetane1 and in their cocrystallized form, but not in the case of the components taken separately. The mechanism by which the impacts cause the luminescence is considered. It was shown that the luminescence is not triboluminescence, but is chemiluminescence induced by the decomposition of compound1.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 1159–1162, May, 1996.     

Chemiluminescence of 1,2-dioxetane. Reaction mechanism uncovered

The thermal decomposition of 1,2-dioxetane and the associated production of chemiluminescent products, model for a wide range of chemiluminescent reactions, has been studied at the multistate multiconfigurational second-order perturbation level of theory. This study is in qualitative and quantitative agreement with experimental observations with respect to the activation energy and the observed increase of triplet and singlet excited products as substituents are added to the parent molecule. The, previously incomplete, reaction mechanism of the chemiluminescence of 1,2-dioxetane is now rationalized and described as mainly due to a particular form of entropic trapping.     

Mechanism of activation and catalysis of chemiluminescence by Eu(fod)3 chelate in thermal decomposition of adamantylideneadamantane-1,2-dioxetane

Complexation of the chelate both with dioxetane and with adamantanone (2), the product of decomposition of dioxetane, have an important effect on chemiluminescence (CL) in thermal decomposition of adamantylideneadamantane-1,2-dioxetane (1) in the presence of Eu(fod)₃ chelate. The stability constants of Eu(fod)₃·1 and Eu(fod)₃·2 complexes were obtained. It was found that Eu(fod)₃ catalyzes and activates chemiluminescent decomposition of1. The rate constant (k₂) of decomposition of the Eu(III)·1 complex was determined from the kinetics of quenching of CL, and the activation parameters were determined from the temperature curve. Luminescence from the⁵D_1-level of the Eu(III) ion was detected in the CL spectrum and was correlated with direct (bypassing the triplet of the ligand) transfer of excitation energy from2 _t* to the luminescent levels of Eu(III) in the geometrically distorted complex Eu(fod)₃·2.Institute of Organic Chemistry, Ural Branch, Russian Academy of Sciences, 450054 Ufa. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 5, pp. 1056–1063, May, 1992.     

CNDO CI calculations of the 1,2-dioxetane to two formaldehydes conversion

Modified CNDO/2 CI calculations, including double and triple excitations, of the 1,2-dioxetane to two formaldehydes reaction indicate that the minimum energy pathway involves the stepwise breaking of the OO bond to form a biradical followed by CC bond breaking rather than the concerted breaking of both CC and OO bonds.     

Singlet oxygenation of cycloheptatriene: isolation and characterization of the 1,2-dioxetane

Tetraphenylporphyrin-sensitized photooxygenation of cycloheptatriene afforded the 1,2-dioxetane ($\text{3a}$) in 9% yield, thus completing the set of possible cycloaddition products; the 1,2-dioxetane ($\text{3a}$) is the precursor to the benzaldehyde product, but not the (2+6)-cycloadduct ($\text{2a}$).