Solvent-Dependent Quenching of the Lowest Excited Singlet State of 9,10-Dichloroanthracene by Ground-State 2,5-Dimethylhexa-2,4-diene Yielding 9-Chloroanthracene in Acetonitrile or the [4+2] Adduct in <i>n</i>-Heptane

Nakayama, Toshihiro; Amijima, Yutaka; Miki, Sadao; Hamanoue, Kumao

doi:10.1246/cl.1997.223

Cited by 3 publications

(2 citation statements)

References 6 publications

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“…(1) (DBA-DMHD)* formed in acetonitrile (ε = 37.5) or acetone (ε = 20.7) decomposes into DBA• -and the DMHD radical cation (DMHD•+), and DBA• -thus generated is an intermediate for DMHD-assisted DBA -> BA debromination; although Saltiel et al [22,23] reported formation of a DCA-DMHD exciplex (by direct excitation of a ground-state DCA-DMHD complex) or a triplex (by a reaction of a DCA-DMHD exciplex with DMHD), no such evidences were obtained by our previous study [19]. (2) [24], the existence of NR• is reasonable but its decomposition into the original compounds (DBA and DMHD) may be a major process owing to the extremely slow photochemical reaction of DBA (cf.…”

Section: Resultsmentioning

confidence: 64%

“…5-1 and kE = 1.1 x 10 9 s-1 ) estimated for an exciplex (formed between DCA* and DMHD) on an assumption of diffusion-controlled quenching (kq = 1.9 x 1010 Μ-1 s -1 ) of DCA* by DMHD [19] as well as those (k' = 2.7 x 109 s -1 and kE = 4.8 x 10 9 s -1 ) of an exciplex formed between DBA* and DMA [13]. kq (stated previously) and kE = 3.8x 10 9 s-1 obtained for (DBA-DMHD)* in ethanol are also comparable with those obtained in acetonitrile, but k' = 9.4 x 10 9 s -1 obtained in the former solvent is about 6.7-times greater than that obtained in the latter solvent.…”

Section: Resultsmentioning

confidence: 99%

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Solvent-Dependent Quenching of the Lowest Excited Singlet State of 9,10-Dibromoanthracene by Ground-State 2,5-Dimethylhexa-2,4-Diene Yielding 9-Bromoanthracene or the [4+2] Adduct

1998

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Irrespective of the dielectric constant (ε) or the hydrogen-bonding ability of a pure solvent, the lowest excited singlet state (DBA*) of 9,10-dibromoanthracene (DBA) is quenched by ground-state 2,5-dimethylhexa-2,4-diene (DMHD) giving rise to the appearance of an exciplex emission. By means of sub-picosecond and nanosecond laser photolysis as well as steady-state photolysis, however, the following solvent-dependent results are obtained; (1) in acetonitrile (ε = 37.5) and acetone (ε = 20.7), an exciplex (DBA-DMHD)* formed between DBA* and DMHD generates the DBA radical anion (DBA' -) as an intermediate for formation of 9-bromoanthracene (BA) from DBA; (2) in ethanol (ε = 24.6), 2-propanol (ε = 19.9), 1-octanol (ε = 10.3), diethyl ether (ε = 4.34), and heptane (ε = 1.92)" a neutral radical species (NR') generated by decomposition of (DBA-DMHD)* (or by a reaction of DBA* with DMHD) is an intermediate for formation of a dibenzobicyclo[2.2.2]octadiene-type compound (a [4+2] adduct); (3) both DBA'-and NR' are generated in methanol (ε = 32.7) but the rate (v) of BA formation upon steady-state photolysis of DBA in the presence of 1 M DMHD decreases in the order of v(acetonitrile, ε = 37.5) > v(acetone, ε = 20.7) > methanol, ε = 32.7). It thus can be concluded that the mechanism of exciplex decomposition and the reaction of DBA* with DMHD are affected by not only the dielectric constant of a pure solvent but also its hydrogen -bonding ability.

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Section: Resultsmentioning

confidence: 64%

Section: Resultsmentioning

confidence: 99%

Solvent-Dependent Quenching of the Lowest Excited Singlet State of 9,10-Dibromoanthracene by Ground-State 2,5-Dimethylhexa-2,4-Diene Yielding 9-Bromoanthracene or the [4+2] Adduct

1998

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Excited-state dynamics for interpretation of the solvent-dependent photochemistry of 9,10-dichloroanthracene in the presence of 2,5-dimethylhexa-2,4-diene

Nakayama

Nagahara

Miki

et al. 2000

Journal of Photochemistry and Photobiology A: Chemistry

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2,5-Dimethyl-2,4-hexadiene induced photodechlorination of 9,10-dichloroanthracene

Saltiel

Smothers

Schanze

et al. 2009

Photochem Photobiol Sci

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Photochemical formation of 9-chloroanthracene (MCA) from 9,10-dichloroanthracene (DCA) is observed in the presence of 2,5-dimethyl-2,4-hexadiene (DMH) in acetonitrile (AN). The mechanism of the reaction was investigated using kinetics, deuterium labeling, and quenching techniques. Contrary to conclusions in a recent publication, our work supports the salient features of the mechanism we had proposed earlier. DCA is photostable in degassed AN in the absence of DMH. When DMH is added, irradiation of DCA at 365 or 404 nm converts it quantitatively to MCA. The photoreaction is strongly inhibited when low concentrations of molecular oxygen or 1,2,4,5-tetracyanobenzene are also present. Results from fluorescence quenching studies along with kinetics parameters from the dependence of DCA loss and MCA formation quantum yields on [DMH] implicate participation of the DCA/DMH singlet exciplex, the DCA/(DMH) 2 triplex and the DCA radical anion (DCA ∑ -) as intermediates in the photodechlorination. Results from experiments using deuterated DMH, deuterated AN, and AN containing D 2 O or H 2 O show that the 10-H of MCA is introduced by protonation of DCA ∑ -. Contrary to a recent report, there is no radical pathway to MCA via dissociation of DCA ∑to chloride and MCA ∑ radical. Changes in the absorption spectrum of DCA in AN with increasing [DMH] suggest that the static quenching of DCA fluorescence at high [DMH] is due primarily to nearest neighbour quenching instead of DCA/DMH ground state complex formation.

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Solvent-Dependent Quenching of the Lowest Excited Singlet State of 9,10-Dichloroanthracene by Ground-State 2,5-Dimethylhexa-2,4-diene Yielding 9-Chloroanthracene in Acetonitrile or the [4+2] Adduct in n-Heptane

Cited by 3 publications

References 6 publications

Solvent-Dependent Quenching of the Lowest Excited Singlet State of 9,10-Dibromoanthracene by Ground-State 2,5-Dimethylhexa-2,4-Diene Yielding 9-Bromoanthracene or the [4+2] Adduct

Solvent-Dependent Quenching of the Lowest Excited Singlet State of 9,10-Dibromoanthracene by Ground-State 2,5-Dimethylhexa-2,4-Diene Yielding 9-Bromoanthracene or the [4+2] Adduct

Excited-state dynamics for interpretation of the solvent-dependent photochemistry of 9,10-dichloroanthracene in the presence of 2,5-dimethylhexa-2,4-diene

2,5-Dimethyl-2,4-hexadiene induced photodechlorination of 9,10-dichloroanthracene

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