Radical Cations of Sterically Hindered Phenols as Intermediates in Radiation-Induced Electron Transfer Processes

Abstract

The radical cations of several preferably sterically hindered phenols have been observed through the radiationinduced electron transfer from the phenol (ArOH) to the parent cations of nonpolar solvents (n-and iso-butyl chloride, cyclohexane, freon-113). For p-methoxyphenol and its 2,6-di-tert-butyl-substituted derivative, ArOH •+ has been characterized after radiolysis at 77 K by EPR and optical absorption spectroscopies. Their broad optical absorption bands at λ ) 430 and <310 nm agree well with those seen at room temperature after pulse radiolysis of the phenol solutions in n-butyl chloride. Generally, also the other phenols studied show similar absorption spectra, but the bands are not so pronounced as in the case of the p-methoxy-substituted ones. Electron transfer from the phenols to n-butyl chloride radical cation proceeds with a rate constant of (1.5-2.0) × 10 10 dm 3 mol -1 s -1 at 293 K. In the case of phenols containing a further functional group distant from the phenol aromatic ring (phenyl acrylate, amine groups), depending on their ionization potential, after the primary ionization intramolecular charge transfer phenomena from or to the phenol unit are observed. ArOH •+ decay under dissociation to phenoxyl radicals (ArO • ) and protons. In the 266 nm laser flash photolysis under ionizing conditions (absorption of two UV photons) in aqueous solutions of the phenols, phenoxyl radicals and solvated electrons are observed, whereas in n-butyl chloride solution ArOH •+ of almost of the studied phenols were found to exist in the nanosecond time range.

Highly Conjugated p‐Quinonoid π‐Extended Tetrathiafulvalene Derivatives: A Class of Highly Distorted Electron Donors

“…Details of the equipment and the data acquisition have been described elsewhere. [37] Dosimetry was based on optical observation of the solvated electron (after 100 ns) in slightly alkaline solution calibrated with G % 2.6 (G denotes the number of species per 100 eV, or the approximate mm concentration per 10 J of absorbed energy). The radical concentration generated per pulse varied in the range (1±3) î 10 À5 m.…”

Sulfur rich electron donors – formation of singlet versus triplet radical ion pair states featuring different lifetimes in the same conjugate

“…35,36,39 This transient absorption decays rapidly giving rise to a new set of transient absorptions, one covering the visible part of the optical spectrum and one in the NIR – see Fig. S10 †.…”

The reaction mechanism of poly[4-hydroxystyrene-co-4-(1,1,1,3,3,3-hexafluoro-2-hydroxypropyl)-styrene]

“…16,30 It is well known that the radical cations of phenol derivatives are easily deprotonated. 31 It was suggested that PHS radical cations in resist films are deprotonated through an ion-molecular reaction assisted by hydrogen bonding. 27 FTIR studies of PHFHPS have probed that PHFHPS molecules also form hydrogen bonding.…”