Triplet Acetophenone Research Articles

Triplet state photochemistry and the three-state crossing of acetophenone within time-dependent density-functional theory

Even though time-dependent density-functional theory (TDDFT) works generally well for describing excited states energies and properties in the Franck-Condon region, it can dramatically fail in predicting photochemistry, notably when electronic state crossings occur. Here, we assess the ability of TDDFT to describe the photochemistry of an important class of triplet sensitizers, namely, aromatic ketones. We take acetophenone as a test molecule, for which accurate ab initio results exist in the literature. Triplet acetophenone is generated thanks to an exotic three-state crossing involving one singlet and two triplets states (i.e., a simultaneous intersystem crossing and triplet conical intersection), thus being a stringent test for approximate TDDFT. We show that most exchange-correlation functionals can only give a semi-qualitative picture of the overall photochemistry, in which the three-state crossing is rather represented as a triplet conical intersection separated from the intersystem crossing. The best result overall is given by the double hybrid functional mPW2PLYP, which is even able to reproduce quantitatively the three-state crossing region. We rationalize this results by noting that double hybrid functionals include a larger portion of double excitation character to the excited states.

Theoretical study of the photochemical generation of triplet acetophenone

Acetophenone has a rich photochemistry, which strongly depends on the absorbing state. For example, the excitation to the lowest singlet excited state (S1) leads to a triplet population with a phosphorescence quantum yield of one, while the excitation to S2 leads to photocleavage reactions. Here, we rationalize the photochemistry of acetophenone after being absorbed into the S1, S2 and S3 states by performing a systematic study of all the singlet and triplet minimum energy structures and state crossings between the relevant electronic states. We calculate these structures at the complete-active space self-consistent field (CASSCF) level of theory and at the correlated extended second-order quasi-degenerate multi-reference perturbation theory (XMCQDPT2), emphasizing the importance of correlation effects in the determination of structures.

ChemInform Abstract: Photo-Heterolysis and -Homolysis of Substituted Diphenylmethyl Halides, Acetates, and Phenyl Ethers in Acetonitrile: Characterization of Diphenylmethyl Cations and Radicals Generated by 248-nm Laser Flash Photolysis

Para-substituted diphenylmethyl halides, acetates, and ethers RPh(R'Ph)CH-X (R, R' = CF3 to OCH3), upon photolysis with -250-nm light in acetonitrile solutions, undergo homolysis and heterolysis of the C-X bond to give the radicals, RPh(R'Ph)CH' (abbreviated as C), and the cations, RPh(R'Ph)CH+ ((2'). Whereas the quantum yields for homolysis (0.2-0.4) are rather independent of the nature of the substituent on the benzene ring, those for heterolysis increase with increasing electron-donator strength from 50.07 for CF3 to 0.3 for OMe. The cationxadical ratios are also dependent on the nucleofugal properties of X. For the halides, the observed hetero1ysis:homolysis ratios correlate with the pK, values of the conjugate acids HX and not with the electron affinities of X'. In acetonitrile, heterolysis is much less endothermic than homolysis. Homolysis and heterolysis can also be effected indirectly by reaction with triplet acetophenone (produced by 308-nm photolysis). Unless stabilized by one or more MeO, the cations decay predominantly by reaction with acetonitrile to give nitrilium ions. However, since this reaction is reversible (shown for the benzhydryl cation), the nitrilium ion contributes only to an insignificant degree to the formation of the final (cation-derived) products, which result from reaction with trace water (main product, benzhydryl alcohol; minor, benzhydrylacetamide). The rate constants for addition of C+ to CH$N are in the range 3.5 X lo5 to 3.8 X IO7 s-I for the cations with R = R' = Me to R = H, R' = CF3. The rate constants for reaction of C+ with halides (ion recombination) are -2 X 1O1O M-l s-' (diffusion control). The radicals C' disappear by dimerization and disproportionation, for which a complete mass balance has been achieved by product analysis for the case of the benzhydryl system. At laser-pulse powers > IO mJ electronically excited radicals, C, are additionally formed in many cases, via absorption of a light quantum by ground-state C'.

Tunnelling corrections in hydrogen abstractions by excited‐state ketones

AbstractHydrogen abstraction from 1‐phenylethanol by triplet acetophenone occurs from both CH and OH bonds. The reaction path of the Interacting‐State Model (ISM) is used with the Transition‐State Theory (TST) and the semiclassical correction for tunnelling (ISM/scTST) to help rationalizing the experimental kinetic results and elucidate the mechanisms of these reactions. The weak exothermicity of the abstraction from the strong OH bond is compensated by electronic effects, hydrogen bonding and tunnelling, and is competitive with the more exothermic abstraction from the α‐CH bond of 1‐phenylethanol. The alkoxy radical formed upon abstraction from OH reacts within the solvent cage and the primary product of this reaction is 1‐phenylethenol. The corresponding kinetic isotope effect is ca. 3 and is entirely consistent with a tunnelling correction ca. 9 for H abstraction. We therefore demonstrate that the tunnelling correction is the major contributor to the kinetic isotope effect. Copyright © 2010 John Wiley & Sons, Ltd.

The photochemical reaction of excited acetophenone and benzaldehyde in the gas phase

The photochemistry of acetophenone and benzaldehyde with hydrogen donors has been studied in the gas phase. The quenching rate constants of the triplet acetophenone and benzaldehyde can be well correlated with the ionization potentials of hydrogen donors. The results suggested that the charge-transfer interaction plays an important role in the gas-phase reaction as in the case of condensed phase reaction. The slopes of Rehm-Weller plot are more stiff in the gas-phase reaction than condensed phase reaction, which indicates higher degree of charge transfer. Secondary amines were consistently better quencher of carbonyl triplet than tertiary amines, and steric effects are probably to be of importance.

Photo-heterolysis and -homolysis of substituted diphenylmethyl halides, acetates, and phenyl ethers in acetonitrile: characterization of diphenylmethyl cations and radicals generated by 248-nm laser flash photolysis

Para-substituted diphenylmethyl halides, acetates, and ethers RPh(R'Ph)CH-X (R, R' = CF3 to OCH3), upon photolysis with -250-nm light in acetonitrile solutions, undergo homolysis and heterolysis of the C-X bond to give the radicals, RPh(R'Ph)CH' (abbreviated as C), and the cations, RPh(R'Ph)CH+ ((2'). Whereas the quantum yields for homolysis (0.2-0.4) are rather independent of the nature of the substituent on the benzene ring, those for heterolysis increase with increasing electron-donator strength from 50.07 for CF3 to 0.3 for OMe. The cationxadical ratios are also dependent on the nucleofugal properties of X. For the halides, the observed hetero1ysis:homolysis ratios correlate with the pK, values of the conjugate acids HX and not with the electron affinities of X'. In acetonitrile, heterolysis is much less endothermic than homolysis. Homolysis and heterolysis can also be effected indirectly by reaction with triplet acetophenone (produced by 308-nm photolysis). Unless stabilized by one or more MeO, the cations decay predominantly by reaction with acetonitrile to give nitrilium ions. However, since this reaction is reversible (shown for the benzhydryl cation), the nitrilium ion contributes only to an insignificant degree to the formation of the final (cation-derived) products, which result from reaction with trace water (main product, benzhydryl alcohol; minor, benzhydrylacetamide). The rate constants for addition of C+ to CH$N are in the range 3.5 X lo5 to 3.8 X IO7 s-I for the cations with R = R' = Me to R = H, R' = CF3. The rate constants for reaction of C+ with halides (ion recombination) are -2 X 1O1O M-l s-' (diffusion control). The radicals C' disappear by dimerization and disproportionation, for which a complete mass balance has been achieved by product analysis for the case of the benzhydryl system. At laser-pulse powers > IO mJ electronically excited radicals, C, are additionally formed in many cases, via absorption of a light quantum by ground-state C'.

Reactions of $$/n\pi ^{\rlap{--} x} /$$ and $$/\pi \pi ^{\rlap{--} x} /$$ states of triplet acetophenone with hydroperoxide moleculesstates of triplet acetophenone with hydroperoxide molecules

The photochemical interaction of triplet acetophenone /TRO/ with α-phenyl ethyl hydroperoxide /HROOH/ has been studied in CCl4 and CH3CN. In CCl4 only the\(/n\pi /^{\rlap{--} x}\) state ofTRO is active abstracting hydrogen from HROOH molecules. In CH3CN both hydrogen abstraction and homolysis of HROOH take place, that is both\(/n\pi /^{\rlap{--} x}\) and\(/\pi \pi /^{\rlap{--} x}\) states of triplet RO play active role.

Variation in the dissociation lifetimes of triplet acetophenone and p-trifluoromethylacetophenone as a function of excitation energy

At low pressures either S 0-S 2 or S 0-S 3 excitation of acetophenone (I) and p-trifluoromethylacetophenone (II) leads to a cleavage with nearly unit efficiency. This photodissociation accounts for the short lifetimes of vibrationally excited lead II. RRKM calculations indicate that the critical energy in both cases is ≈20 kcal mol , somewhat greater than the endothermicity.

SENSITIZATION OF THE PHOSPHORESCENCE OF INDOLE THROUGH INTRAMOLECULAR ENERGY TRANSFER FROM THE TRIPLET STATE OF COVALENTLY LINKED ACETOPHENONE IN RIGID MEDIA AT 77 K

Abstract— In an attempt to study the quenching of the triplet state of acetophenone by indole, we have prepared the compounds containing these chromophores intramolecularly. The emission measurements in rigid glasses at 77 K have indicated that the quenching of the triplet acetophenone is due to intramolecular triplet‐triplet energy transfer to the indole chromophore, resulting in the sensitization of the indole phosphorescence. The efficiency of the energy transfer has reached ca. 100% in ethanol glasses, while it has been suggested that in methylcyclohexane glasses, the indole chromophore except for 1‐methyl derivative is subjected to strong interaction with the acetophenone chromophore other than electronic energy transfer.

Evidence against reversible triplet energy transfer between acetophenone and norbornene

Kinetic absorption and emission spectroscopy has been used to monitor the decay of triplet acetophenone produced in benzene by both pulse radiolysis and pulse laser photolysis techniques. The dependence of this decay on the concentrations of norbornene and acetophenone shows that, in contrast to a previous claim, triplet energy transfer between acetophenone and norbornene is not reversible. These data, together with quantum yield measurements, indicate that in this system ground state acetophenone quenches triplet acetophenone and either triplet norbornene or a ketone triplet—olefin exciplex by processes which do not involve energy transfer.

Triplet state quenching involving charge transfer interactions between N-methyl indole and aromatic carbonyl compounds in benzene solution

In laser photolysis experiments N-methyl indole quenches the triplet states of several aromatic carbonyl compounds including some with lower energy triplet states with rate constants in the range (0.02–10)× 109 dm3 mol–1 s–1. Quenching by N-methyl indole is shown to be either exclusively or partially due to electronic energy transfer from either triplet acetophenone or triplet xanthone respectively, and the sensitized spectrum assigned to the triplet state of N-methyl indole is given. Quenching of the other triplet carbonyls by N-methyl indole is shown to depend on the energy predicted for the charge transfer state of each interacting pair of compounds with N-methyl indole as the potential electron donor. In ethanol solution quenching of the triplet state of xanthone by N-methyl indole is demonstrated to occur via electron transfer leading to the formation of separate ions.Pulse radiolysis of indole, 3-methyl indole and N-methyl indole in benzene solution gives short lived triplet states of these compounds, the spectra of which have been determined. Quenching of triplet N-methyl indole by various compounds with higher and lower triplet states was investigated following pulse radiolysis in benzene solution. The rate constants for quenching of triplet N-methyl indole were also shown to depend on charge transfer interactions and evidence for energy transfer was obtained only in cases where the predicted charge transfer states lie at much higher energies than the locally excited triplet states. The reasons why charge transfer interactions cause rapid relaxation of triplet exciplexes are discussed.

Effects of solvent and substituents on the absorption spectra of triplet acetophenone and the acetophenone ketyl radical studied by nanosecond laser photolysis

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTEffects of solvent and substituents on the absorption spectra of triplet acetophenone and the acetophenone ketyl radical studied by nanosecond laser photolysisHanspeter Lutz, Emilienne Breheret, and Lars LindqvistCite this: J. Phys. Chem. 1973, 77, 14, 1758–1762Publication Date (Print):July 1, 1973Publication History Published online1 May 2002Published inissue 1 July 1973https://doi.org/10.1021/j100633a006RIGHTS & PERMISSIONSArticle Views844Altmetric-Citations143LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (670 KB) Get e-Alerts

Slow quenching of triplet ketones by alkyl thiols

Butanethiol quenches triplet acetophenone with a rate constant of 1·4 × 107 M–1 s–1 which is slow enough to be used for trapping radical products without quenching excited states.

Transfer of triplet state energy from acetophenone to rare earth ions

The bright line emission of certain rare earth ions, energised by intermolecular transfer from triplet acetophenone, has been studied and the intensity is found to depend upon rare earth ion concentration according to a modified Stern—Volmer equation. Self-quenching of rare earth ions is observed.