Reactive States of Acridine for the Photoreduction in Tetrahydrofuran

The photoreduction of acridine in tetrahydrofuran (THF) has been investigated by the steady light experiment and also by the flash technique. The quantum yields in the aerated and deaerated solution were 0.12 and 0.36 respectively. The former value is referred to molecular mechanism while the difference of the two, 0.24, to radical mechanism. It was established that the sensitized reaction occurs with biacetyl (T(n–π*), 19700cm−1) as a triplet energy donor. The probability factor β with which the produced T(π–π*) of acridine (15840 cm−1) reacts with THF was found to be 0.6. Anthracene T(π–π*), 14700cm−1) was found to act as a triplet energy acceptor and to reduce the photoreduction. From the decrease of the quantum yield caused by the addition of anthracene, the quantum yield via the lowest T(π–π*) of acridine was evaluated as 0.06. By combining this value with the above β-value, the apparent has proved to be 0.1. This very small value compared with the values presented for other solvents (benzene0.25, water0.24, ethanol0.29) leads to the conclusion that in THF, T(n–π*) is also a reactive state for the photoreduction. Further, an interesting aspect of the radical mechanism was elucidated from the comparison of ΦR (quantum yield due to radical mechanism) and ΦO2 (quantum yield of oxygen consumption).