Photoionization of DNA and RNA Bases, Nucleosides and Nucleotides Through a Combination of One- and Two-photon Pathways upon 266 nm Nanosecond Laser Excitation¶

Abstract

The 266 nm nanosecond laser photolysis of various purine and pyrimidine derivatives results in their photoionization (PI) as one of the primary photochemical pathways. Electron photoejection occurs through a combination of one- and two-photon mechanisms. The PI values depend on the substituents attached to the chromophore of the base. The net PI of the purine bases at 266 nm are of the same order of magnitude (10(-2)) as those of the pyrimidine bases under similar experimental conditions. The monophotonic component is approximately one-third of the net PI yield of the bases. A nonrelaxed singlet excited state intermediate is tentatively proposed for this pathway. It is proposed that this state is significantly stabilized by water solvation, transforming it into a charge transfer to solvent state from which the hydrated electron evolves.

Two-color spectroscopy of UV excited ssDNA complex with a single-wall nanotube photoluminescence probe: Fast relaxation by nucleobase autoionization mechanism

“…The most abundant SWNT species in the CoMoCat samples are known to be (6,5) nanotubes (see Fig.7). The MD simulation was done on a fragment of (6,5) SWNT with two intertwinned ssDNA oligomers (GT) n where n = 30, as shown in Fig.6 (upper inset).…”

“…1a). Note that (6,5) is the most abundant SWNT species in our CoMoCat samples. In view of the computational resource limitations, the CNDO calculations were performed for only a part of the MD system that included a single unit cell of the SWNT (41 Å in length) and the DNA bases overlaying the unit cell with their coordinates extracted from the MD frames (see SI for detail).…”

“…While the recombination mechanisms have been studied quite extensively[1, [3][4][5], DNA autoionization [6] has received less attention, partially due to the fact that AI in solution involves charge transfer from DNA to the surrounding water solvent [7][8][9]. The irregular, dynamically changing structure of the solvent makes quantitative modeling of experiments and theoretical predictions of AI rates and mechanisms extremely complicated [10,11].…”

“…(20,21) into (27) and making use of the short-cut notations given by Eqs. (24,28) we obtain the following formula: The normalized differential PL, δI, for a (6,5) nanotube is shown in Fig.9 along with the excitation efficiency function M/(M + 1) and the normalized function ∆ γ . For a (6,5) tube the DNA induced exciton quenching can reach above 30% of the total non-radiative decay rate.…”

“…(24,28) we obtain the following formula: The normalized differential PL, δI, for a (6,5) nanotube is shown in Fig.9 along with the excitation efficiency function M/(M + 1) and the normalized function ∆ γ . For a (6,5) tube the DNA induced exciton quenching can reach above 30% of the total non-radiative decay rate. Other chiralities show similar differential PLE spectra with two main features: on the UV side each δI spectrum has a negative band (note that the abscissa axis is reversed for δI) around 530 nm where the intensity of one-color (vis) excitation PL exceeds the two-color PL intensity.…”