Aqueous solutions of adenine (A), deoxyadenosine (dA) and deoxyadenosine 5'-monophosphate (dAMP) were studied in room temperature by femtosecond fluorescence upconversion. The fluorescence decays cannot be described by single exponentials. They consist of an ultrafast component (230 fs for A, < 100 fs for dA and dAMP) and a slower one (8 ps for A, 0.5 ps for dA and dAMP). The slow component constitutes 95% of the total fluorescence (time-integrated) for the base while only 24% for the nucleoside or the nucleotide. The initial fluorescence anisotropy is 0.30 +/- 0.03 for A, 0.25 +/- 0.05 for dA and dAMP. The anisotropy of the A fluorescence partially decays during its lifetime due to rotational diffusion. (C) 2002 Published by Elsevier Science B.V.