7-Irradiated organic glasses, electrons

Table I. G Values (100 e.v. yields) of Trapped Electrons in y-Irradiated Organic Glasses at 77 °K.

TABLE 6.4 Radiation Yields (G Values) of Stabilized Electrons in Organic Glasses Under /-Irradiation at 77 K... 

Ionic processes of monomers, nitroethylene, n-butylvinylether and styrene, in organic glass matrices of 2-methyltetrahydrofuran, 3-methyl-pentane and n-butylchloride irradiated by y-rays at 77° K, are studied by observing the electron spin resonance spectra of trapped electrons and ion radicals formed from the solute monomers. The primary ionic intermediates are the trapped electrons and their counterpart, cation radicals of matrix molecules. However, in 2-methyltetrahydrofuran glass, the anionic processes of solute monomers resulting from the trapped electrons proceed selectively. On the contrary, only the cationic processes proceed selectively in n-butylchloride glass. Both processes are able to occur in 3-methylpentane glass. 

Confirmation that the emitting species in phosphorescent organic molecules is a triplet has come from several sources. In the 1940s it was discovered that a solution of fluorescein in boric acid glass became paramagnetic under intense irradiation more recently it has been shown that the paramagnetism and the phosphorescence decay at identical rates when irradiation ceases. The electron paramagnetic resonance (EPR) technique is capable of detect-... 

Smith, D, R., and J. J. Pieroni Detection of Trapped Electrons in Organic Glasses after Gamma Irradiation at 4.2° K by Electron Spin Resonance Spectroscopy. Can. J. Chem. 43, 2723 (1967). 

Properties and Reactions of Electrons in /-Irradiated and Photoionized Organic Glasses... 

Only a few conductivity measurements on organic glasses have been reported. Albrecht et ah (14, 15) studied the photoconductance of 3-methylpentane (3-MP) while Viseall and Willard (18) determined the conductivity of the same compound after y-irradiation. In an earlier paper (16) we reported the observations on the conductivity of irradiated 2-methyltetrahydrofuran. The presence of trapped electrons and ions that can be freed by illumination or thermally can be inferred from the current increase caused by their movements. The temperature dependence of the conductivity in these glasses suggested the occurrence of structural changes and indicated the existence of traps with different depths. 

Localized electrons in organic glasses exhibit an optical absorption spectrum similar to that of electrons in liquid hydrocarbons. In 3-methylhexane irradiated with Co-y-radiation or fast electrons, the absorption maximum occurs between 1600 and 2000 nm (Klassen et al., 1971). Trapped electrons can be mobilized by light of a suitable wavelength. The electrons are promoted out of the trap and they contribute to the conductivity imtil they become retrapped. The spectral dependence of the photocurrent due to trapped electrons in glassy methyl cyclohexane is shown in... 

B. M. Glass, A. P. Combs, Rapid Parallel Synthesis Utilizing Microwave Irradiation Article E0027, Fifth International Electronic Conference on Synthetic Organic Chemistry" (Eds. C. O. Kappe, P. Merino, A. Marzinzik, H. Wennemers, T. Wirth, J. J. Vanden Eynde, S.-K. Lin), CD-ROM edition,... 

Glass, B.M. and Combs, A.P., Rapid parallel synthesis utilizing microwave irradiation (Article E0027), In Kappe, C.O., Merino, R, Marzinzik, A., Wennemers, H., Wirth, T., Vanden Eynde, J.J. and Lin, S.K. (Eds.), Fifth International Electronic Conference on Synthetic Organic Chemistry, MDPI, Basel, Switzerland, 2001, CD-ROM edition. 

In this connection it is noteworthy that smooth defluorination of some fluoroquinolones (used as antibacterial drugs) is obtained both at the cathode and by photolysis in the presence of sodium sulfite in aqueous solution, as it is shown for enoxacin (65) in Scheme 47 [142]. The 6,8-difluoro derivative lomefloxacin is selectively defluorinated at position 8 by cathodic reduction. Electron capture of electrons by 5-halouracils in neutral organic and aqueous glasses leads to species characterized as cr radical anions (more advanced in the path towards cleavage) with the iodo and bromo derivatives, whereas n radical anions are formed from the chloro and fluoro derivatives [143]. The radical anion of 2-chlorothiophene (obtained by irradiation in the crystal state) is of the cr type [144]. 

---