Solvent effects upon the phosphorescence lifetimes and photoreactivity of butyrophenone

Rauh, R. D.; Leermakers, Peter A.

doi:10.1021/ja01011a007

Cited by 51 publications

(56 citation statements)

References 3 publications

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“…A value of tp = 5 ms reflects a lower lying 3nn* state relative to the 3nn* state. The observed slight increase of T~ of acetophenone with increasing polarity of the glass is well documented in the literature [32, 331 and has been interpreted as a mixing of the nn* and nn* states [34,35]. Consequently, we have to correlate the long lifetimes of the a-phenoxyacetophenones in this class with a lowest 'nn* state, as shown in Fig.…”

Section: No Substituent In the Acetophenone Partsupporting

confidence: 51%

The Photochemistry of α‐Phenoxyacetophenones Investigated by Flash‐CIDNP‐spectroscopy

Palm

Dreeskamp

Bouas‐Laurent

et al. 1992

Ber Bunsenges Phys Chem

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The photochemistry of 14 different substituted or-phenoxyacetophenones (1) was studied by CIDNPspectroscopy using an XeCl excimer laser (308 nm) and a 250 MHz 'H-NMR spectrometer. To characterize the excited states the electronic absorption and emission spectra as well as disappearance quantum yields were investigated also. -Two reaction channels were established: 1) P-cleavage from the singlet state;and 2) the formation of acetophenones via the respective enol forms where the origin of the polarization remains unclear. It is concluded that these are the main reaction channels, since all products formed show polarizations in the CIDNP-spectra. -In contrast to the current assumptions for the typical acetophenone reaction of (1) leading to the P-cleavage, we are led to interprete the CIDNP-spectra of (1) as a result of a reaction due to the phenoxy part with all characteristics of a photo-Claisen reaction.

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Section: No Substituent In the Acetophenone Partsupporting

confidence: 51%

The Photochemistry of α‐Phenoxyacetophenones Investigated by Flash‐CIDNP‐spectroscopy

Palm

Dreeskamp

Bouas‐Laurent

et al. 1992

Ber Bunsenges Phys Chem

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“…Electron-donating substituents and polar solvents tend to stabilize the π,π* state,11 which is generally far less reactive toward H-atom abstraction than the n,π* state with its half vacant, non-bonding p orbital on the carbonyl oxygen 6. To our surprise, 14 , having three electron donating substituents (and largely a π,π* configuration), still underwent photoenolization in acetonitrile, although the reaction was much less efficient (by a factor of 10 compared with those carried out in aqueous organic solvents).…”

Section: Anhydrous Media: the Photoenolization Pathwaymentioning

confidence: 99%

The Power of Solvent in Altering the Course of Photorearrangements

et al. 2011

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A clean bifurcation between two important photochemical reactions through competition of a triplet state Type II H-abstraction reaction with a photo-Favorskii rearrangement for (o/p)-hydroxy-o-methylphenacyl esters that depends on the water content of the solvent has been established. The switch from the anhydrous Type II pathway that yields indanones to the aqueousdependent pathway producing benzofuranones occurs abruptly at low water concentrations (~8%). The surprisingly clean yields suggest that such reactions are synthetically promising.An intramolecular Type II reaction of alkylphenones, especially 2-methylacetophenoes, produces high yields of photoenols that have been shown to be valuable reactive intermediates. 1 When a leaving group (X) is present in the α-position of 2-alkylacetophenones (1), longer-lived (E)-photoenols liberate HX to give indanones 2 (2 ; Scheme 1) that can be employed as precursors to elaborate products used in synthetic methodology. 3 Likewise, the photo-Favorskii rearrangement of α-substituted phydroxyacetophenones (3) to p-hydroxyphenylacetic acid (4), discovered more recently, has enjoyed success in a variety of applications because of its rapid release of nucleofuges (Scheme 1). 4 Both reactions have exhibited very good photochemical efficiencies and are relatively free of side reactions that produce complicated product mixtures. The similarity of the chromophores, the common triplet state origin for reaction, and the extensive understanding of the mechanistic photochemistry 5 have prompted us to explore the intersection of the photochemical pathways to uncover which parameters control the pathway followed by a chromophore common to both. It is a rare occurrence in organic photochemistry when one can completely and cleanly divert the reaction or rearrangement pathway from a single product type to an alternative * parkbs@dongguk.edu; givensr@ku.edu; klan@sci.muni.cz. Supporting Information Available:Experimental details and characterization data for products are provided. This material is available free of charge via the Internet at http://pubs.acs.org. 3a Since it is well known that electron donating hydroxy and methoxy groups suppress Type II reactivity 6 and nearly as well known that the photo-Favorskii rearrangement has a strong affinity for water, 4k,7 we assumed that these two reaction pathways might be separated by the water content of the solvent media. In this work, the analogs of 4-hydroxyphenacyl derivatives with good leaving groups necessary for the photo-Favorskii process were fitted with 2-methyl substituent for efficient Type II hydrogen abstraction reaction to compete with the photo-Favorskii rearrangement. As an extension, a similar design, in which the 2-hydroxyphenacyl derivatives were fitted with a 6-methyl group, was also examined. NIH Public Access Synthesis of Phenacyl Esters4-Hydroxy-2-methyl (9a-c) and 2-hydroxy-4,6-dimethylphenacyl (14) esters, and the corresponding benzyl (10) and methyl (13) ethers were prepared by α-bromination of acetophen...

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“…A number of different explanations have been proposed [1][2][3][4][5][6][7][8][9][10][11][12], including emission from the ketone and a photoproduct, emission from the ketone in two or more different sites in the t Present address: Department of Chemistry, University of Rochester, Rochester, New York.…”

Section: Introductionmentioning

confidence: 99%

Primary photophysical and photochemical processes of 2,4,5-trimethylbenzaldehyde in crystalline durene

et al. 1977

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The temperature dependence (10-160 K) of the phosphorescence lifetimes and intensities of 2,4,5-trimethylbenzaldehyde (TMB) in crystalline durene have been investigated. Two phosphorescence bands (407"5 and 411'2 nm) are observed to grow in with increasing temperature, reach a maximum intensity, and decrease in intensity at higher temperatures. Exponential phosphorescence decays are observed in the 10 to 95 K and 110 to 160 K ranges, while non-exponential decays are observed in the 95 to 110 K region. Ultra-violet photolysis, particularly at higher temperatures, is seen to decrease the intensity of the infra-red carbonyl stretching band at 1703 cm -x, but not the one at 1684 cm -1. A model in which two inequivalent sets of TMB molecules in the durene lattice undergo their own unique photochemical and photophysical processes is suggested to explain the results. It is proposed that within each site the lower, predominantly Z~rrr* state of the anti TMB conformer is in thermal equilibrium with the higher-lying 3nrr* state of the syn conformer which is formed by out-of-plane rotation of the aldehyde group in the excited state. In one site, intramolecular photoenol formation occurs via thermal activation from the 3nr* of the syn conformer, while in the other site intermolecular hydrogen abstraction occurs, leading to the simultaneous production of a photoenol and a duryl radical. This model is shown to be consistent with previous knowledge of the primary photochemical processes of TMB in durene.

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Solvent effects upon the phosphorescence lifetimes and photoreactivity of butyrophenone

Cited by 51 publications

References 3 publications

The Photochemistry of α‐Phenoxyacetophenones Investigated by Flash‐CIDNP‐spectroscopy

The Photochemistry of α‐Phenoxyacetophenones Investigated by Flash‐CIDNP‐spectroscopy

The Power of Solvent in Altering the Course of Photorearrangements

Primary photophysical and photochemical processes of 2,4,5-trimethylbenzaldehyde in crystalline durene

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