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-methylacridinium perchlorate (AcrH+), 2,4,6-triphenylpyrylium tetrafluoroborate (TPP+), and the p-methoxyphenyltropylium ion (3) was studied with the help of steady state photolysis and laser flash spectroscopy. Intermediates detected revealed the occurrence of electron transfer. It affords the formation 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 and 2 are transformed into the corresponding tropylium ions (3 and 4). Electrochemically, both processes, 2→4 and 4→2, were performed by altering the current direction, and several 2→4→2 cycles were achieved.

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