Chemiexcitation Yield Research Articles

Role of conical intersection seam topography in the chemiexcitation of 1,2-dioxetanes.

Chemiexcitation, the generation of electronic excited states by a thermal reaction initiated on the ground state, is an essential step in chemiluminescence, and it is mediated by the presence of a conical intersection that allows a nonadiabatic transition from ground state to excited state. Conical intersections classified as sloped favor chemiexcitation over ground state relaxation. The chemiexcitation yield of 1,2-dioxetanes is known to increase upon methylation. In this work we explore to which extent this trend can be attributed to changes in the conical intersection topography or accessibility. Since conical intersections are not isolated points, but continuous seams, we locate regions of the conical intersection seams that are close to the configuration space traversed by the molecules as they react on the ground state. We find that conical intersections are energetically and geometrically accessible from the reaction trajectory, and that topographies favorable to chemiexcitation are found in all three molecules studied. Nevertheless, the results suggest that dynamic effects are more important for explaining the different yields than the static features of the potential energy surfaces.

Comparative study of the chemiluminescence of coelenterazine, coelenterazine-e and Cypridina luciferin with an experimental and theoretical approach

Imidazopyrazinone is a typical scaffold present in marine bioluminescence, in which thermal energy is converted into excitation energy in an enzyme-catalyzed reaction. In fact, the imidazopyrazinone scaffold is a common link among organisms of eight phyla. The characterization of the light emission mechanism is essential for the development of future applications in bioimaging, bioanalysis and biomedicine. Herein, we have studied the chemiluminescent reaction of three commercially-available imidazopyrazinones (Cypridina luciferin, Coelenterazine and Coelenterazine-e) in several aprotic solvents at different pH. We have found that at acidic pH only DMF and DMSO consistently present high light emission, while chemiluminescence in other solvents is negligible. We have attributed this to the inability of most solvents to allow for the deprotonation of the imidazopyrazinone core, thereby preventing the oxygenation step. We have also observed that increasing the pH of the solution leads to the inhibition of chemiluminescence, which we attributed to the deprotonation of the dioxetanone intermediate, as the neutral species is the one associated with efficient chemiexcitation. We have also observed that the pKa of dioxetanone increases with the dielectric constant of the medium. Finally, our work indicated that the chemiexcitation yield increases with increasing polarity of the medium, due to a reduced transition dipole moment associated with S0 → S1 transition.

Efficient Generation of Chemiluminescence during the reduction of manganese(IV) ions with lactic acid

The kinetics and mechanism of chemiluminescence during the reduction of manganese(IV) ions with lactic acid in an H2SO4–AcOH medium are studied. Kinetic spectrophotometric measurements are used to determine the profiles of change in the concentrations of Mn(IV) and Mn(III) ions during the reaction. The results from kinetic spectrophotometric measurements are compared to the light yield kinetics. The quantum chemiluminescence and chemiexcitation yields reach record values.

Chemiluminescence quantum yield in permanganate reduction reactions in acid medium

Chemiluminescence quantum yields for the reactions of permanganate with oxalic, tartaric, and citric acids; hydrazine; KBr; and FeSO4 in aqueous solutions of sulfuric acid have been measured. The maximum quantum yield reaches 1.2 × 10−5 einstein/mol with the chemiexcitation yield being 2%. Hence, the relatively low chemiluminescence quantum yield is due to a low yield of light emission by chemiexcited particles, rather than the low chemiexcitation yield.

The Hammett correlation between distyrylbenzene substituents and chemiluminescence efficiency providing various ρ-values for peroxyoxalate chemiluminescence of several oxalates

Abstract Peroxyoxalate chemiluminescence (PO-CL) was investigated using eight oxalates with various phenol moieties and the distyrylbenzene (DSB) fluorophores with various substituents. The ρ -values in the Hammett correlation between the substituent constants (σ p + ) of the DSBs and the singlet chemiexcitation yields ( Φ S ) for the PO-CL reactions varied from −0.50 to −1.01 depending on the oxalate structure, and the reactive oxalates tended to afford the higher absolute ρ -values but with a few exceptions. Based on the CIEEL mechanism, these experimental observations suggest that the aryloxy groups still remain in the 1,2-dioxetanones (DOTs), which are the postulated high-energy intermediates, and control the electronic properties of DOTs as electron-acceptors. The LUMO energies of the DOTs calculated by the ab initio method with a B3LYP/6-31g(d) basis set reveal that the lower the DOT-LUMO energies, the higher the absolute ρ -values were provided for the corresponding oxalates, as predicted by the frontier molecular orbital (FMO) theory. Thus, the chemical species interacting with the DSBs would be not unitary and will be DOTs.

ChemInform Abstract: Thermolysis of 3-Methyl-3-(o-aryl)-1,2-dioxetanes: Activation Parameters and Chemiexcitation Yields.

3-Methyl-3-(o-tolyl)-1,2-dioxetane 1 and 3-methyl-4-(o-bromophenyl)-1,2-dioxetane 2 were synthesized in low yield by the β-bromo hydroperoxide method. The activation parameters were determined by the chemilumin-escence method (for 1 ΔG‡ = 24.7 ± 0.3 kcal/mol, ΔH‡ = 25.4, ΔS‡ = + 1.9 e.u., k60 = 3.4 × 10−4s−1; for 2 ΔG‡ = 24.7 ± 0.4 kcal/mol, ΔH‡ = 24.7, ΔS‡ = 0.0 e.u., k60 = 4.1 × 10−4s−1). Thermolysis of 1–2 directly produced high yields of excited triplets as expected for this type of dioxetane [triplet chemiexcitation yields (ϕ7) for 1 0.03; for 2 0.02; the ϕT/ϕS ratios were estimated to be approximately 200 for both compounds]. The effect of ortho-aryl substituents was inconsistent with electronic effects. The ortho substitution in 1–2 resulted in a marked increase in stability of the dioxetanes. The results are discussed in relation to a diradical-like mechanism.

Synthesis of 1-(3- tert-butyldimethylsiloxy)phenyl-5,5-dimethyl-2,7,8-trioxabicyclo[4.2.0]octanes: new dioxetanes giving high chemiexcitation yields in thermolysis and in fluoride-induced CIEEL-decay

Dioxetanes with annelated six-membered ring, 1-(3- tert-butyldimethylsiloxy)phenyl-5,5-dimethyl-2,7,8-trioxabicyclo[4.2.0]octanes ( 2a– 2c ) were synthesized by singlet oxygenation of the corresponding aryl-substituted dihydropyrans ( 3 ). Thermolysis of 2a– 2c gave the corresponding ketoesters ( 5a– 5c ) as a normal decomposition product together with a considerable amount (23–26%) of ester ( 6 ) derived from Norrish type I reaction of the triplet-excited ester ( 5 ). On the other hand, treatment with tetrabutylammonium fluoride (TBAF) in DMSO induced rapid decomposition of 2 to emit blue light in high chemiexcitation yield (72–75%) of the oxyanion of a ketoester ( 10 ). These results show that the chemiexcitation efficiency of dioxetanes ( 2 ) was higher than that of their five-membered ring analog ( 1 ) not only for thermolysis and but also for the base-induced CIEEL.

Base-induced chemiluminescence of 5-tert-butyl-1-(4-hydroxybenz[d]oxazol-6-yl)-4,4-dimethyl-2,6,7-trioxabicyclo[3.2.0]heptanes: chemiluminescence–chemiexcitation profile in aqueous medium

Bicyclic dioxetanes bearing a 2-aryl-4-hydroxybenz[d]oxazol-6-yl moiety (3a–3c) and their 2-alkyl-analogs (3d, 3e) were synthesized. All these dioxetanes (3a–3e) afforded light with high efficiency on treatment with tetrabutylammonium fluoride in acetonitrile. In the NaOH–H2O system, chemiluminescence efficiency (ΦCIEEL) for alkyl-analogs (3d, 3e) decreased markedly, while ΦCIEEL for 3a–3c was still considerably high. Fluorescence study revealed that the marked decrease of ΦCIEEL for alkyl-analogs would be attributed to a synergetic effect of decreased chemiexcitation yield and fluorescence yield of the emitter in NaOH–H2O system.

Solvent-Cage Effect (Viscosity Dependence) as a Diagnostic Probe for the Mechanism of the Intramolecular Chemically Initiated Electron-Exchange Luminescence (CIEEL) Triggered from a Spiroadamantyl-Substituted Dioxetane

The excitation step of the intramolecular CIEEL generation in the triggered cleavage of spiroadamantyl-substituted dioxetane has been studied. The electron back-transfer (BET) process versus the direct chemiexcitation of the phenolate-anion emitter have been considered as mechanistic alternatives. The observed solvent-cage effect on the CIEEL generation, manifested by the increase of the singlet chemiexcitation yield at increased viscosity, provides evidence that the BET process operates in the intramolecular CIEEL mechanism.

Chemiluminescence and catalysis of decomposition of dimethyldioxirane adsorbed from the gas phase on silipore containing tris(bipyridyl)ruthenium complex Ru(bpy)3Cl2 and 9,10-diphenylanthracene

The kinetics of decomposition of dimethyldioxirane (DMD) adsorbed from the gas phase on the silipore surface was studied by the chemiluminescence (CL) technique. The lower boundary of the CL yield in the reaction of DMD decomposition (4·10−9 Einstein mol−1) and chemiexcitation yield of methyl acetate (4·10−4) were estimated. Chemiluminescence upon decomposition of DMD on the silipore surface in the presence of activators of CL such as tris(bipyridyl)ruthenium complex Ru(bpy)3Cl2 and 9,10-diphenylanthracene was revealed. Ru(bpy)3Cl2 activates the luminescence according to chemically induced electron exchange mechanism.

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.

Luminol chemiluminescence in micellar media

The light reaction of luminol with sodium hypochlorite is reported in cetyltrimethylammonium chloride (CTAC) micelles. The chemiluminescence and chemiexcitation yields in this medium are reported, together with the chemical yields and the fluorescence quantum yield of 3- aminophthalate, the primary emitter. The CTAC molecules cause both chemical and photophysical quenching; however, the chemiexcitation yields are higher than in homogeneous aqueous media due to the less polar microenvironment of the micellar Stern region. Based on the chemiluminescence decay curves, the apparent pseudo-first-order rate constants are reported and the dependence on the surfactant concentration is shown to be in accordance with the pseudophase kinetic model. Employing this model the ion exchange constant between OCl − and Cl −, the micellar rate constant and the luminol-CTAC binding constant are also reported.

Thermolysis of 3‐methyl‐3‐(o‐aryl)‐1,2‐dioxetanes: Activation parameters and chemiexcitation yields

Abstract3‐Methyl‐3‐(o‐tolyl)‐1,2‐dioxetane 1 and 3‐methyl‐4‐(o‐bromophenyl)‐1,2‐dioxetane 2 were synthesized in low yield by the β‐bromo hydroperoxide method. The activation parameters were determined by the chemilumin‐escence method (for 1 ΔG‡ = 24.7 ± 0.3 kcal/mol, ΔH‡ = 25.4, ΔS‡ = + 1.9 e.u., k60 = 3.4 × 10−4s−1; for 2 ΔG‡ = 24.7 ± 0.4 kcal/mol, ΔH‡ = 24.7, ΔS‡ = 0.0 e.u., k60 = 4.1 × 10−4s−1). Thermolysis of 1–2 directly produced high yields of excited triplets as expected for this type of dioxetane [triplet chemiexcitation yields (ϕ7) for 1 0.03; for 2 0.02; the ϕT/ϕS ratios were estimated to be approximately 200 for both compounds]. The effect of ortho‐aryl substituents was inconsistent with electronic effects. The ortho substitution in 1–2 resulted in a marked increase in stability of the dioxetanes. The results are discussed in relation to a diradical‐like mechanism.

High-temperature decomposition of tetramethyldioxetane: measurements of gas-phase chemiexcitation yields

The yields of electronically excited acetone from high-temperature decomposition of gas-phase tetramethyldioxetane (TMD) are reported. High temperatures are achieved by using infrared-sensitized excitation of TMD. Emission studies are used to obtain the yield of excited singlet acetone, /Phi//sub S/ = 0.017 (/plus minus/ 0.008). This value is approximately a factor of 2 higher than that reported in solution. A lower limit for the yield of triplet acetone is determined by using transient absorption studies, /Phi//sub T/ />=/ 0.10 (/plus minus/ 0.03). This value is comparable to previous results in solution. The lifetime of triplet acetone observed in the present experiment is approximately 5 ..mu..s, almost 2 orders of magnitude shorter than the lifetime of thermalized triplet acetone at low pressures. The short lifetime is attributed to electronic quenching by the infrared-absorbing gas CH/sub 3/F, with an estimated rate constant of 5 x 10/sup -13/ cm/sup 3//(molecule s).

ChemInform Abstract: Thermolysis of 1,2‐Dioxetanes: Activation Parameters and Chemiexcitation Yields for Unsymmetric Cis/Trans Isomers.

ChemInformVolume 19, Issue 2 Preparative Organic Chemistry ChemInform Abstract: Thermolysis of 1,2-Dioxetanes: Activation Parameters and Chemiexcitation Yields for Unsymmetric Cis/Trans Isomers. A. L. BAUMSTARK, A. L. BAUMSTARK Dep. Chem., Lab. MBS, Georgia State Univ., Atlanta, GA 30303, USASearch for more papers by this authorC. A. RETTER, C. A. RETTER Dep. Chem., Lab. MBS, Georgia State Univ., Atlanta, GA 30303, USASearch for more papers by this authorK. TEHRANI, K. TEHRANI Dep. Chem., Lab. MBS, Georgia State Univ., Atlanta, GA 30303, USASearch for more papers by this authorC. KELLOGG, C. KELLOGG Dep. Chem., Lab. MBS, Georgia State Univ., Atlanta, GA 30303, USASearch for more papers by this author A. L. BAUMSTARK, A. L. BAUMSTARK Dep. Chem., Lab. MBS, Georgia State Univ., Atlanta, GA 30303, USASearch for more papers by this authorC. A. RETTER, C. A. RETTER Dep. Chem., Lab. MBS, Georgia State Univ., Atlanta, GA 30303, USASearch for more papers by this authorK. TEHRANI, K. TEHRANI Dep. Chem., Lab. MBS, Georgia State Univ., Atlanta, GA 30303, USASearch for more papers by this authorC. KELLOGG, C. KELLOGG Dep. Chem., Lab. MBS, Georgia State Univ., Atlanta, GA 30303, USASearch for more papers by this author First published: January 12, 1988 https://doi.org/10.1002/chin.198802065AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume19, Issue2January 12, 1988 RelatedInformation

The Effect of 4-Hydroxyl Substituent on the Singlet Chemiexcitation Yield in Base-catalyzed Air Oxidation of 3,5-Dichlorophenylpyruvic Acids

Abstract In base-catalyzed air oxidation of substituted phenylpyruvic acids, an excited singlet product is generated from 3,5-dichloro-4-hydroxyphenylpyruvic acid (1) but excited triplet products from 3,5-dichlorophenyl-(2) and 3,5-dichloro-4-methoxyphenylpyruvic acid (3). According to the reaction scheme proposed, the singlet chemiexcitation yield from 1 and the triplet yields from 2 and 3 are 1·2×10−4, 8.3×10−4, and 6.7×10−4, respectively. A discussion is made on the difference in spin state selectivity between 1 and 2 or 3.