Photoreduction of aryltrophylium ions

The reduction of aryl-substituted tropylium ions in deaerated acetonitrile solution at room temperature can be achieved by photoinduced electron trans fer from 9,10-dihydro-10-methylacridine (AcrH(2)) 2,4,6-triphenyl-4H-pyran (TPPH), 10,10'-dimethyl-9,9'-bisacridane (AcrH)(2), or 2,2',4,4',6,6'-hexam ethyl-4,4'-bi-(4H-pyran) (TMP)(2) to 4-methoxyphenyl tropylium perchlorate (1) and 4-dimethylaminophenyl tropylium perchlorate (2). Thermal reactions play a role only in the case of AcrH(2) and TPPH. The light-induced reduction was studied with the aid of steady state photol ysis and laser flash spectroscopy. A mechanism involving the photoionizatio n of (AcrH)(2) is proposed.