Rostislav F. Vasil'ev

Chemically Initiated Electron Exchange Luminescence of Silyloxyaryl‐Substituted Spiroadamantyl Dioxetanes: Kinetics and Excited State Yields

Abstract— The kinetics of the fluoride‐induced decomposition of the thermally stable silyloxyaryl‐substituted spiroadamantyl dioxetanes 1a,b and the excited state formation of this chemically initiated electron exchange luminescence (CIEEL) have been investigated. Two limiting kinetic regimes flash and glow have been identified, which depend on the fluoride concentration, the first at high, the second at low [F‐] triggering, whose detailed kinetic analysis affords the rate constants for the deprotected dioxetanes 2a,b cleavage in acetonitrile and dimethyl sulfoxide and chemiluminescence measurements the CIEEL and phen‐olate 4 (CIEEL emitter) excitation yields. Chloro‐substi‐tution in the spiroadamantyl dioxetane does not affect the deprotection step k2 but leads to a ca five‐fold faster cleavage of the deprotected dioxetane 2, while the chemiexcitation yield is the same for both dioxetanes. The energies of the first excited singlet and triplet states of the emitting phenolate 4 were estimated by AM1 configuration interaction calculations with explicit consideration of acetonitrile as solvent (self‐consistent reaction field approach). The first excited singlet and triplet state of the CIEEL emitter phenolate 4 possess π,π* character, as suggested by the π‐type molecular orbitals and the large singlet‐triplet energy gap. The chemiexcitation of both singlet and triplet states of the excited phenolate 4 is feasible during the dioxetanes 1a,b cleavage, but the experimentally determined high singlet excitation yields suggest that preferentially the phenolate 4 singlet state is populated in the fluoride ion‐triggered CIEEL process.

ENERGY TRANSFER-ENHANCED CHEMILUMINESCENCE OF ADAMANTANONE (n,π*) AND ESTER (π,π*) SINGLET AND TRIPLET EXCITED STATES IN THE THERMOLYSIS OF SILYLOXYARYL-SUBSTITUTED SPIROADAMANTYL DIOXETANES†

Abstract—

Facile chemiluminescence assay for antioxidative properties of vegetable lipids: fundamentals and illustrative examples

The general approach disclosed herein opens the new possibilities of exploiting the oxidation processes followed by chemiluminescence (CL) emission for the assessment of an antioxidant potential of natural lipid materials and enables determination of the amount and strength of lipid-borne antioxidants in one experiment. The reliability of the analytical procedure is completely unaffected by an inevitable entering of oxidizable lipid portions into the probe chemiluminescent mixture, which is exemplarily illustrated for the case of vegetable oils which served as sources of antioxidant-containing lipids. As a matter of fact, the difference in the effective radical-scavenging rate constants, determined for the antioxidative constituents of the sunflower and corn oils, perfectly matches the distinction of their qualitative tocopherol contents. In addition to the antiradical activity of lipid samples, the antioxidant potential of the latter may be modified by their influence on hydroperoxide stability, as it has been also demonstrated in the present work.

Back electron transfer in electron-exchange chemiluminescence of oxyaryl-substituted spiroadamantyl dioxetane, an analog of firefly bioluminescence

The viscosity dependence of the excitation yield of the singlet oxybenzoate anion, an emitter of electron-exchange chemiluminescence of oxyaryl-substituted spiroadamantyl dioxetane, a chemical analog of firefly bioluminescence, was studied. At 299, K the excitation yield increases from 8 to 23% as the content of diphenylmethane in its mixture with benzene increases to 97%. This effect was quantitatively interpreted in terms of a probabilistic model of the solvent-cage effect, assuming that the chemiexcitation results from the back electron transfer between the products of chemically initiated decomposition of the starting reagent.

A kinetic chemiluminescence study of the antioxidants evolved from polymeric materials into the gaseous phase

Abstract Evolution of efficient peroxyl (ROO) acceptors from polymers into the gaseous phase was studied. The oxygen- containing gas was passed over a polymer sample and bubbled through a chemiluminescent probe solution of a hydrocarbon (RH: diphenylmethane, ethylbenzene or cyclohexane). Chemiluminescence was excited on dis- proportionation of ROO and chemically quenched due to the reaction of ROO with dissolved acceptors. Acceptors were detected at 290–350 K over polyolefins, black and silicone rubber, linoleum and rubber sediments on the leaves of plants, etc. The samples exhibit increased ability or acquire the ability to generate acceptors after treatment to induce their oxidation. Acceptors have been detected in the ambient air; the probable sources are polymeric fabrics, parts and waste, etc. in the environment. The concentration of acceptors may reach 10 -7 –10 −8 M in the air, which decreases on breathing. The rate constant for the acceptor-ROO reaction (approximately 10 9 M −1 s −1 ) is close to the diffusion-limited rate, whereas reactions of acceptors with hydrocarbons, molecular oxygen, strong hydrogen donors and stable free radicals (galvinoxyl) are very slow (less than 10 2 M −1 s −1 ) as is the self-reaction of acceptors in the gaseous phase (5 x 10 2 M −1 s −1 ). These unusual kinetic properties can be explained if the acceptors are assumed to be radical products of polymer destruction with bulky substituents at a partly alelocalized electron centre.

Chemiluminescence of Cigarette Smoke: Salient Features of the Phenomenon.

The study disclosed herein provides for the first time a detailed experimental support for the general mechanism of the cigarette‐smoke‐derived chemiluminescence, as an example par excellence of the excited‐state generation in a chemically complex aerosol medium. The mechanism involves chemiexcitation in a unimolecular transformation of the smoke‐borne free radical species. However, the concentration of these radicals, [r∙] , obeys a bimolecular (second‐order) kinetics and depends on a particulate‐phase content (total particulate matter, TPM) of the cigarette smoke. The decrease in [r∙] with increasing the TPM amount manifests radical‐scavenging propensity of the smoke particulate phase. Astonishingly, no energy transfer takes place from the primary excited light‐emitting species to luminophoric molecules abundant in the smoke. The reported results build up fundamentals of a facile chemiluminescence assay for free radical properties of the smoke. The experimental approaches developed for this study are of general scope and may be used for mechanistic elucidation of the excited‐state generation in chemical systems and environments of an arbitrary complexity.

Effects of polarity and temperature on photoluminescence of a europium(III) chelate

The relative photoluminescence yield for (1,10-phenanthroline)europium(III) tris-thenoyltrinuoroacetonate (Eu(tta)3Phen). an efficient enhancer of chemiluminescence, has been measured under the conditions (temperatures and solvents) specific for the oxidation of hydrocarbons. The yield is independent of viscosity and the presence of a heavy atom in the solvent, but the higher the polarity of the medium, the more the yield decreases as the temperature increases. The effect is interpreted as an acceleration of radiationless deactivation occurringvia the mechanism of electron transfer from a ligand to the excited Eu3+ ion.

Excitation of chemiluminescence in a model reaction of diphenylmethane oxidation. Evaluation of the efficiency and semiempirical calculations

The absolute yields (ϕ*) of excitation of the triplet benzophenone, a product of disproportionation of peroxyls in the chemiluminescent oxidation reaction of diphenylmethane, were measured. The ϕ* value is independent of the temperature and viscosity of the medium, but decreases with increase in its polarity: it is 0.003 in CCl4 and 0.0015 in MeCN. Semiempirical MNDO calculations of the structure of intermediates and the energy profile of their decomposition were carried out. A conclusion was made that the excitation of the3nπ* state of the ketone occurs during the decomposition of the intermediate tetroxide Ph2CHOOOOCHPh2 after the transition state, but before isolation of the Ph2COOO biradical, which thereafter decomposes to benzophenone and O2.

Chemiluminescence in the oxidation of unsaturated organic compounds in solution

ConclusionsIn the oxidation of unsaturated compounds, certain processes that form various electronexcited products make various contributions to chemiluminescence (CL). In pure olefins there is no CL; in actual samples CL is due to traces of peroxides. In the initiated olefin oxidation the low CL intensity is due to the excitation yield and the low emission yield of the primary emitter, an alkenone. Activator-intensified CL can be used to determine the kinetics of the radical-chain oxidation of olefins.

The mechanism of the initiating action of nitrogen dioxide in the oxidation of 2,7-dimethyloctane by molecular oxygen

1. The brief insufflation of nitrogen dioxide at the beginning of the reaction substantially accelerates the oxidation of 2,7-dimethyloctane by molecular oxygen. 2. As a result of the interaction of nitrogen dioxide with 2,7-dimethyloctane there is formed a relatively stable intermediate initiator. 3. The mechanism of the acceleration consists in the decomposition of the intermediate initiator into radicals which leads to an increase in the rate of initiation. 4. The intermediate initiator gradually disappears during the course of the oxidation but it acts for a long time in comparison with the time of initiation.