Radical-cations pulse-radiolytic generation

Spectroscopic evidence for the transient formation of the trans-stilbene radical cation could be obtained when colloidal TiOj suspended in an acetonitrile solution containing trans-stilbene (a species which should also be exothermically oxidized by a TiO valence band hole) was excited with a laser pulse The observed transient was identical in spectroscopic features and in lifetime with an authentic sample of the stilbene cation radical generated in the same medium via pulse radiolytic techniques. That the surface influences the subsequent chemistry of this species can be seen in the distribution of products observed under steady state illumination, Eq. (4) 2 . ... 

Oxidation The radiation-chemically induced ionization of chlorinated hydrocarbons, i.e., dichloroethane (DCE) leads to the initial generation of the corresponding solvent radical cation, [DCE] ". The electron affinity of the latter is sufficient to oxidize the fullerene moiety ([60]fullerene E1/2 = +1.26 versus Fc / Fc ). Pulse radiolytic experiments with [60]fullerene in nitrogen-saturated or aerated DCM solutions yielded a doublet with maxima at 960 and 980 nm (Figure 1) (12-18). This fingerprint is identical to that detected in photolytic oxidation experiments and that computed in CNDO/S calculations. Rate constants for the [60]fullerene oxidation are typically very fast with estimated values IC7 > 2 x 10 ° M s. The 7t-radical cation is short-lived and decays via a concentration-dependent bimolecular dimerization reaction with a ground state molecule (kg = 6 x lO M s ) (13). 

Phenothiazine radicals have been generated in various radiolytic experiments. Pulse radiolysis of phenothiazine in aerated cycloalkane solutions gives rise to phenothiazinyl (251). ° The mode of oxidation is believed to involve abstraction of H from the heterocycle by cycloalkylperoxyl radicals. Under similar conditions, 10-methylphenothiazine gives 261. Pulse radiolysis of phenothiazine in acetonitrile has also been documented. The reduction of phenothiazine dyes under radiolytic conditions has been reported. Several years ago, Ayscough and Thomson obtained paramagnetic products from X-irradiation of acid alcoholic solutions of Methylene Blue and other thiazine dyes. Low-resolution ESR spectra of the corresponding cation-radicals were recorded. 

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