2-aminopurine (2AP) is a DNA base analogue with a structure similar to that of adenine and guanine, and has been used as an internal fluorescent probe for the study of DNA solvation and structural dynamics. We have performed DFT calculations to aid in the assignment of intermediates observed in picosecond time-resolved infrared spectroscopy following the two-photon ionisation of 2AP in neutral and acidic aqueous solutions. Our results shed light on the nature of the species formed when DNA is damaged by radiation.