Picosecond fluorescence of nucleic acid bases

After excitation with UV femtosecond laser pulses, the dynamics of the first excited singlet states of nucleic acid bases in polar solutions were directly determined by fluorescence detection with a sufficient time resolution using a sensitive streak camera. The single-shot detection followed by a numerical synchronization allowed the study of emission lifetimes of singlet states, even with low quantum yields of the order of 10−4. The measured fluorescence decays in a few picoseconds. The typical values for the S1-state lifetimes in water are between 6 and 9 ps for the purine bases and between 1 and 2 ps for the pyrimidines. In the nucleosides and nucleotides of purine bases, the lifetimes decrease towards 1 ps. Studying less polar solvents, such as ethanol and acetonitrile, especially for adenine dissolved in ethanol, a remarkable lifetime of 16 ps was found.