Ultrafast decay and hydration dynamics of DNA bases and mimics

The ultrafast decay of the excited-state of DNA bases, reported here and elsewhere [Peon & Zewail, Chem. Phys. Lett. 348 (2001) 255], makes very difficult the probing of the full hydration dynamics in DNA. Here we present studies of the natural DNA base mimic, 2-aminopurine (2AP), whose excited-state decay is much longer, in water and, for comparison, in bulk ethanol. Guided by these solvation results, which directly reflect the role of orientational and translational diffusion, we reexamine the ultrafast decay rates for the natural nucleotides and nucleosides. The results are important for the mechanism of energy disposal in DNA.