DIPOLE-MOMENTS AND LIFETIMES OF EXCITED TRIPLET-STATES OF ANILINE AND ITS DERIVATIVES IN NONPOLAR-SOLVENTS

Dipole moments have been determined for excited triplet states of aniline and its related compounds (dimethylaniline (DMA), diethylaniline (DEA), diphenylamine (DPA), and triphenylamine (TPA)) in nonpolar solvents by analyzing microwave dielectric absorption signals observed in 308-nm laser flash photolysis at room temperature. For all the compounds investigated, the dipole moment increases upon excitation; in benzene, the values are 2.1, 3.0, 3.1, 2.1, and 2.2 D for aniline, DMA, DEA, DPA, and TPA, respectively. The values for TPA and DPA in n-hexane and cyclohexane are not much different from those in benzene. The values from a semiempirical molecular orbital calculation can be compared to these experimental ones, and the polarity change upon excitation is mostly associated with the electron transfer from the N atom to the adjacent C atom in the phenyl ring. In contrast, the values in CCl4 are much different and should not be referred to those for the triplet states. In dioxane, the values become higher than those in benzene, probably due to the effect of hydrogen bonding. The lifetimes of the excited triplet states have been determined, 1.2, 0.7, 1.0, 27, and 60 mu s, for aniline, DMA, DEA, DPA, and TPA, respectively, in benzene.