Excited states decay of the A-T DNA: a PCM/TD-DFT study in aqueous solution of the [(9-methyl-adenine).sub.2].1[(1-methyl-thymine).sub.2] stacked tetramer

The behavior of the lowest energy excited states of A-T B-DNA is analyzed by using a realistic model, namely a double strand tetramer formed by two thymine-adenine stacked pairs in aqueous solution. The long living components of the excited state population of (dA).(dT) oligomers have corresponded to a dark excimer produced by intermonomer charge transfer between two stacked adenine bases, whereas adenine-thymine proton transfer has played a minor role in the excited state decay.