Time-resolved resonance Raman spectroscopy and density functional theory investigation of the photochemistry of 4-chloroaniline in the solution phase

Abstract

Time-resolved resonance Raman spectra and density functional theory computations for the intermediates formed following the photolysis of 4-chloroaniline in both acetonitrile and methanol solvents are reported. Laser excitation of 4-chloroaniline in methanol produced two transient species with different lifetimes. The end-of-pulse transient species was identified as the triplet aminophenyl cation with a lifetime of 800 ns. The other species was assigned to the aniline radical cation with a lifetime of 28 μs. In oxygen quenching experiments, the lifetime of the aniline radical cation was reduced to 1.7 μs. Only one transient species (which had a concentration-dependence) was observed in acetonitrile. The lifetime of this species varied from 30 μs at a relatively high concentration to 100 μs at a lower concentration. The resonance Raman frequencies and the lifetime of this species matches very well with the longer lifetime species observed in methanol. The transient intermediate that was observed in both acetonitrile and methanol solvents was assigned to the same species, the aniline radical cation. The Raman shifts of our experimental results match reasonably well with the theoretical calculated frequencies. All of these assignments for the transient species are in good agreement with the results previously reported from transient absorption spectroscopy experiments. We briefly discuss the structures, properties and reactivity of the aniline radical cation and the triplet aminophenyl cation observed in the time-resolved resonance Raman experiments.