Photodissociation of p-ethyl- and p-(α-hydroxyethyl)toluene in solution

Fujiwara, Mai; Mishima, Kenji

doi:10.1039/b004079g

Cited by 2 publications

(2 citation statements)

References 33 publications

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“…This is similar to the reported rate constants for the formation of the T 1 of benzene and toluene. Furthermore, laser flash photolysis of p-methylphenylethanol has been reported to produce its T 1 , which has an absorption between 300 and 400 nm and a lifetime of 2 ms. [40] Because 3 and 4 have similar S 0 absorption, but 4 is not as an efficient sensitizer as 3, we propose that the smaller rate constant for intersystem crossing in 4 causes it to be both a singlet and triplet sensitizer for azidoadamantane. Furthermore, the shorter lifetime of the T 1 of 2 causes it to be a less effective sensitizer than 1.…”

Section: Laser Flash Photolysismentioning

confidence: 87%

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Phenylethanol derivatives as triplet sensitizers for 1‐azidoadamantane

Ranaweera

Rajam

Guđmundsdóttir

2011

J of Physical Organic Chem

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Laser flash photolysis, phosphorescence and density functional calculations were used to characterize the triplet excited states of phenylethanol derivatives 1, 2, 3 and 4. In acetonitrile, the triplet excited states of these alcohols were formed with rate constants on the order of ~107 s–1 and decayed with rate constants between 105 and 106 s–1. The energies of these triplet excited states were between 80 and 83 kcal/mol. Furthermore, 3 can be used as a triplet sensitizer for alkyl azides to form triplet nitrene intermediates. Copyright © 2011 John Wiley & Sons, Ltd.

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Section: Laser Flash Photolysismentioning

confidence: 87%

“…This is similar to the reported rate constants for the formation of the T 1 of benzene and toluene. Furthermore, laser flash photolysis of p ‐methylphenylethanol has been reported to produce its T 1 , which has an absorption between 300 and 400 nm and a lifetime of 2 µs …”

Section: Laser Flash Photolysismentioning

confidence: 99%

Phenylethanol derivatives as triplet sensitizers for 1‐azidoadamantane

Ranaweera

Rajam

Guđmundsdóttir

2011

J of Physical Organic Chem

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Triplet- vs. singlet-state imposed photochemistry. The role of substituent effects on the photo-Fries and photodissociation reaction of triphenylmethyl silanes

Zarkadis

Georgakilas

Perdikomatis

et al. 2005

Photochem Photobiol Sci

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The photochemistry of three structurally very similar triphenylmethylsilanes 1, 2, 3 [p-X-C(6)H(4)-CPh(2)-SiMe(3): X = PhCO, 1; H, ; Ph(OCH(2)CH(2)O)C, 3] is described by means of 248 and 308 nm nanosecond laser flash photolysis (ns-LFP), femtosecond LFP, EPR spectroscopy, emission spectroscopy (fluorescence, phosphorescence), ns-pulse radiolysis (ns-PR), photoproduct analysis studies in MeCN, and X-ray crystallographic analysis of the two key-compounds 1 and 2. The photochemical behavior of 1, 2 and 3 is discussed and compared with that of a fourth one, 4, bearing on the p-position an amino group (X = Me(2)N) and whose detailed photochemistry we reported earlier (J. Org. Chem., 2000, 65, 4274-4280). Silane 1 undergoes on irradiation with 248 and 308 nm laser light a fast photodissociation of the C-Si bond giving the p-(benzoyl)triphenylmethyl radical (1*) with a rate constant of k(diss)= 3 x 10(7) s(-1). The formation of 1* is a one-quantum process and takes place via the carbonyl triplet excited state with high quantum yield (Phi(rad)= 0.9); the intervention of the triplet state is clearly demonstrated through the phosphorescence spectrum and quenching experiments with ferrocene (k(q)= 9.3 x 10(9) M(-1) s(-1)), Et(3)N (1.1 x 10(9) M(-1) s(-1)), and styrene (3.1 x 10(9) M(-1) s(-1)) giving quenching rate constants very similar to those of benzophenone. For comparative reasons radical 1* was generated independently from p-(benzoyl)triphenylmethyl bromide via pulse radiolysis in THF and its absorption coefficient at lambda(max)= 340 nm was determined ([epsilon]= 27770 M(-1) cm(-1)). We found thus that the p-PhCO-derivative 1 behaves similar to the p-Me(2)N one (the latter giving the p-(dimethylamino)triphenylmethyl radical with Phi(rad)= 0.9), irrespective of their completely different ground state electronic properties. In contrast, compounds 2, 3 that bear only the aromatic chromophore give by laser or lamp irradiation both, (i) radical products [Ph(3)C* and p-Ph(OCH(2)CH(2)O)C-C(6)H(4)-C(*)Ph(2), respectively] after dissociation of the central C-Si bond (Phi(rad)= 0.16), and (ii) persistent photo-Fries rearrangement products (of the type of 5-methylidene-6-trimethylsilyl-1,3-cyclohexadiene) absorbing at 300-450 nm and arising from a 1,3-shift of the SiMe(3) group from the benzylic to the ortho-position of the aromatic ring (Phi approximately 0.85 for 2). Using fs-LFP on 2 we showed that the S(1) state recorded at 100 fs after the pulse decays on a time scale of 500 fs giving Ph(3)C* through C-Si bond dissociation. In a second step and within the next 10 ps trityl radicals either escape from the solvent cage (the quantum yield of Ph(3)C* formation Phi(rad)= 0.16 was measured with ns-LFP), or undergo in-cage recombination to photo-Fries products. Thus, singlet excited states (S(1)) of the aromatic organosilanes (2, 3) prefer photo-Fries rearrangement products, while triplet excited states (1, 4) favor free radicals. Both reactions proceed via a common primary photodissociation step (C-Si bond homolysis) and diffe...

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Photodissociation of p-ethyl- and p-(α-hydroxyethyl)toluene in solution

Cited by 2 publications

References 33 publications

Phenylethanol derivatives as triplet sensitizers for 1‐azidoadamantane

Phenylethanol derivatives as triplet sensitizers for 1‐azidoadamantane

Triplet- vs. singlet-state imposed photochemistry. The role of substituent effects on the photo-Fries and photodissociation reaction of triphenylmethyl silanes

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