22206-01-5Relevant academic research and scientific papers
Laser flash photolysis study of the photochemistry of thioxanthone in organic solvents
Rodrigues, Janaina F.,De Assis Da Silva, Francisco,Netto-Ferreira, Jose? Carlos
scheme or table, p. 960 - 965 (2010/10/21)
The photoreactivity of the triplet excited state of thioxanthone (TX) was investigated employing the laser fash photolysis technique. The wavelength for the absorption maximum and the lifetime of the triplet excited state are solvent dependent. When hydrogen donor solvents were employed, a new band at 410 nm was observed in the triplet absorption spectrum, which was attributed to the ketyl radical derived from thioxantone. Quenching rate constants, kq, ranged from (1.7 0.1) × 106 L mol-1 s-1 for toluene to ca. 109 L mol-1 s-1 for phenol and its derivatives containing polar substituents, as well as for indole, triethylamine and DABCO.
Bimolecular hydrogen abstraction from phenols by aromatic ketone triplets
Lathioor, Edward C.,Leigh, William J.
, p. 291 - 300 (2008/02/05)
Absolute rate constants for hydrogen abstraction from 4-methylphenol (para-cresol) by the lowest triplet states of 24 aromatic ketones have been determined in acetonitrile solution at 23°C, and the results combined with previously reported data for roughly a dozen other compounds under identical conditions. The ketones studied include various ring-substituted benzophenones and acetophenones, α,α,α-trifluoroacetophenone and its 4-methoxy analog, 2-benzoylthiophene, 2-acetonaphthone, and various other polycyclic aromatic ketones such as fluorenone, xanthone and thioxanthone, and encompass n,π*, π,π*(CT) and arenoid π,π* lowest triplets with (triplet) reduction potentials (Ered*) varying from about -10 to -38 kcal mol-1. The 4-methylphenoxyl radical is observed as the product of triplet quenching in almost every case, along with the corresponding hemipinacol radical in most instances. Hammett plots for the acetophenones and benzophenones are quite different, but plots of log log kQ vs Ered* reveal a common behavior for most of the compounds studied. The results are consistent with reaction via two mechanisms: a simple electron-transfer mechanism, which applies to the n,π* triplet ketones and those π,π* triplets that possess particularly low reduction potentials, and a coupled electron-/proton-transfer mechanism involving the intermediacy of a hydrogen-bonded exciplex, which applies to the π,π* ketone triplets. Ketones with lowest charge-transfer π,π* states exhibit rate constants that vary only slightly with triplet reduction potential over the full range investigated; this is due to the compensating effect of substituents on triplet state basicity and reduction potential, which both play a role in quenching by the hydrogen-bonded exciplex mechanism. Ketones with arenoid π,π* states exhibit the fall-off in rate constant that is typical of photoinduced electron transfer reactions, but it occurs at a much higher potential than would be normally expected due to the effects of hydrogen-bonding on the rate of electron-transfer within the exciplex.
Photoreduction of Triplet Thioxanthone by Amines: Charge Transfer Generates Radicals That Initiate Polymerization of Olefins
Yates, Stephen F.,Schuster, Gary B.
, p. 3349 - 3356 (2007/10/02)
Thioxanthone triplet is photoreduced by amines via a charge-transfer or exciplex intermediate to thioxanthyl ketyl radical.This ion pair can be observed by nanosecond laser spectroscopy in polar solvents with easily oxidized dimethylaniline as reductant.The intermediacy of this species in benzene was indicated by the correlation of triplet quenching rates with amine ionization potential and by the absence of a significant isotope effect in triplet quenching by tert-butylamine-d2.In contrast, tri-n-butylstannane reacts more rapidly than its ionization potential would dictate and exhibits a larger isotope effect.Addition of methyl methacrylate does not significantly alter the rates of decay for the ion pair of ketyl radikal.Product studies show that the aminomethyl radical PhN(CH3)CH2* is the principal initiator of olefin polymerization.
