Intermediates in the nanosecond pulse radiolysis of triphenylamine solutions in cyclohexane

Abstract

The pulse radiolysis of solutions of triphenylamine (TPA) in cyclohexane has been investigated using nanosecond time resolution. In addition to the transient absorption at 620 nm which has been previously observed in microsecond pulse radiolysis and which is assigned to the N-phenyldihydrocarbazole (DHC) derivative, the following species have been identified: singlet TPA, fluorescence maximum 365 nm, mean lifetime 4.5 ns; triplet TPA, absorption maximum 520 nm, mean lifetime 38 ns; triplet N-phenyldihydrocarbazole, absorption maximum 430 nm, mean lifetime 330 ns; the TPA+ radical cation, absorption maximum 640 nm. The rate constants for the reaction of TPA1, TPA3 and DHC3 with O2 have been measured to be 1.8 × 1010 1.3 × 1010 and 7 × 109 M–1 s–1 respectively. For a 10–2 M TPA solution the yield and decay kinetics of TPA+(Iµ640= 14 000 M–1 cm–1) are the same as found for the biphenyl negative ion in a 10–2 M biphenyl in cyclohexane solution. The effects of NH3 and N2O on the yields of intermediates indicate ion recombination following charge scavenging by TPA to be the major source of TPA1 and TPA3.