Generation of aryltropylium ions from the corresponding bitropyls by electrochemical and photoinduced electron-transfer

The photoinduced electron transfer from aryl-substituted bitropyls bearing 4-methoxyphenyl (1) and 4-(N,N-dimethylamino)phenyl substituents (2) to N-m ethylacridinium perchlorate (AcrH(+)), 2,4,6-triphenylpyrylium tetrafluorob orate (TPP+), and the p-methoxyphenyltropylium ion (3) was studied with the help of steady state photolysis and laser flash spectroscopy. Intermediate s detected revealed the occurrence of electron transfer. It affords the for mation of radical cations of 1. C-C bond cleavage occurring in the radical cation can compete with back electron transfer. In this way, compounds 1 an d 2 are transformed into the corresponding tropylium ions (3 and 4). Electr ochemically, both processes, 2-->4 and 4-->2, were performed by altering th e current direction, and several 2-->4-->2 cycles were achieved.