Formation, excited state and electron transfer properties of the phenoxyl radical of 4,4'-thiodiphenol

Mohan, Hari ; Mittal, J. P. (1999) Formation, excited state and electron transfer properties of the phenoxyl radical of 4,4'-thiodiphenol Journal of Photochemistry and Photobiology A: Chemistry, 124 (3). pp. 119-125. ISSN 1010-6030

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The transient absorption bands (λ max = 335, 500, 650-800 nm) formed on pulse radiolysis of N2O-saturated basic aqueous solution of 4,4'-thiodiphenol (TDPH) are assigned to phenoxyl radical (TDP) formed on one-electron oxidation of phenoxide ion (TDP-) of TDPH. Specific one-electron oxidants (N3, I•-2, Br, CCl3OO) also produced phenoxyl radicals with similar transient absorption spectrum. Phenoxyl radicals are able to undergo electron transfer reaction with N,N,N',N'-tetramethyl-p-phenylenediamine (TMPD) with a bimolecular rate constant of 4.5 × 109 dm3 mol-1 s-1. Pulse radiolysis of N2-saturated TDPH in benzene showed absorption bands at 330, 500, 650-800 nm. The second-order decay of these bands was not affected by oxygen and anthracene, well-known triplet quenchers and the transient spectrum is assigned to phenoxyl radicals formed on fast decay of solute triplets with a G value of 0.29. Benzophenone triplet is able to undergo energy transfer with TDPH with a bimolecular rate constant of 6 × 109 dm3 mol-1 s-1 and formed benzophenone ketyl radical (λ = 545 nm) and phenoxyl radical (TDP, λ = 500 nm) on H atom transfer from TDPH to benzophenone in an intermediate complex. The G value of phenoxyl radicals was determined to be 1.44. Picosecond laser flash photolysis of TDPH in acetonitrile failed to form any transient absorption in 450-900 nm region, supporting that only a small fraction of TDPH triplet decay to phenoxyls. Pulse radiolysis and picosecond laser flash photolysis studies indicate that the triplets of TDPH are highly unstable. The oxidation potential of TDP-/ TDP, H+ couple is estimated to be between 0.265 and 1.03 V.

Item Type:Article
Source:Copyright of this article belongs to Elsevier Science.
Keywords:Transient Absorption Bands; Radiolysis; Electron Transfer Properties
ID Code:25756
Deposited On:04 Dec 2010 11:44
Last Modified:07 Jun 2011 06:48

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