Role of ribose in the initial excited state structural dynamics of thymidine in water solution: A resonance raman and density functional theory investigation

Abstract

Resonance Raman spectra were obtained for thymidine and thymine with excitation wavelengths in resonance with the ∑260 nm band absorption spectrum. The spectra indicate that the Franck-Condon (FC) region photodissociation dynamics of thymidine have multidimensional character with motion predominantly along the nominal C 5=C 6 stretch + C 6-H bend v 17 (δ = 0,75, γ = 468 cm -1 the nominal thymine ring stretch + C 6-H bend + N 1C 1 stretch v 29 (δ = 0.73, γ = 363 cm -1), the nominal thymine ring stretch + C 5-CH 3/ N 1-C 1 stretch v 537 (δ = 0.69, γ = 292 cm -1), and accompanied by the moderate and minor changes in the v 40, v 20 and v 23, v 55, v 60, v 61 v 63 modes. A preliminary resonance Raman intensity analysis was done, and these results for thymidine and thymine were compared to each other. The roles of ribose in the FC structure dynamics of thymidine were explored and the results were used to correlate to its lifetime constants T 1 and r 2 for two nonradiative decay channels. S π/S n conical intersection versus a distorted structure of S π,min in the FC region was briefly discussed. © 2008 American Chemical Society.