PHOTOOXYGENATION OF 1,OMEGA-BIS(DIARYLETHENYL)ALKANES VIA PHOTOINDUCED ELECTRON-TRANSFER - FORMATION OF 1,4-RADICAL CATIONS AND ITS TRAPPING BY MOLECULAR DIOXYGEN

The 9,10-dicyanoanthracene (DCA)-sensitized photooxygenation of 1,omega-bis(diarylethenyl)alkanes (Ar2C=CH(CH2)(n)CH=CAr2) was studied. The photooxygenation of the alkadienes in acetonitrile afforded bicyclic peroxides when Ar = 4-CH3OC6H4, n = 3 and 4. When Ar = 4-CH3OC6H4, n = 2, 5, 8 or Ar = C6H5, n = 3, the photooxygenation did not afford bicyclic peroxides, but gave diaryl ketones. Laser flash photolysis studies indicated that the photooxygenation is initiated by a one-electron transfer from the alkadienes to (1)DCA* and proceeds via 1,4-radical cations that are generated by an intramolecular cyclization between an ethenyl moiety and a radical cation of another ethenyl moiety.