The nature of the electronic excitations capturing centres in the DNA

The spectral peculiarities of the DNA, the polynucleotide poly(dAdT)2, the oligonucleotide d(CCCGGGTTTAAA), the trimer d(ATC) and the low molecular model compounds dGMP, dAMP, dCMP and dTMP were studied. The system of energy sites and electronic processes in the DNA were examined. The lowest excited electronic singlet levels of the DNA were shown to be related with guanine bases, while the lowest excited triplet levels are connected with adenine bases. The nature of the fluorescence and phosphorescence emission centres in the DNA is discussed. It was shown the phosphorescence of the DNA is close to emission of the triplet excitations traps associated with AT-sequences. These centres as well as adenine bases are most photostable. The latter proves to be a successful mechanism for DNA self protection.