Direct measurement of excited singlet-state lifetime in the homologous sequence adenine, adenosine, adenosine 5'-monophosphate and in calf thymus DNA

The excited singlet-state lifetimes of the nucleic acid components adenine, adenosine and adenosine 5'-monophosphate, and also that of calf thymus DNA were determined from transient absorption measurements using a UV-laser flash-photolysis apparatus with subpicosecond time resolution. Excitation at lambda = 280 nm gave for adenine the value 1.6 +/- 0.3 ps. The addition of ribose and the further addition of a phosphate group do not affect the lifetime significantly: the values 1.9 +/- 0.3 and 2.1 +/- 0.3 ps, respectively, were obtained. For calf thymus DNA the lifetime was shorter than the experimental limit of resolution, 0.4 ps.