title: Ultrafast excited state dynamics of allopurinol, a modified DNA base.
abstract: The decay of electronically excited allopurinol riboside was studied through the fluorescence up-conversion technique and high level ab initio calculations. For the allopurinol system with a pyrazolic five-membered ring, we observed an ultrafast decay of the fluorescence signal in water (τ < 0.2 ps), similar to what has been observed for hypoxanthine and inosine (with an imidazolic five-membered ring). These results show that the S(1) dynamics in this type of heterocyclic systems are general and dominated by the distortion in the pyrimidinic six-membered ring with a negligible influence of the rest of the heterocycle. The measurements are consistent with the presence of a highly accessible conical intersection between the S(1) (π-π*) excited state and S(0), as calculated by MR-CIS/CASSCF computations. Our calculations show that the loss of planarity of the six-membered ring is responsible for direct access to the S(1)-S(0) degeneracy region without requiring distortions in the rest of the molecule.
authors: Instituto de Química, Universidad Nacional Autónoma de México, Circuito Exterior, Ciudad Universitaria, México, 04510, D.F., México.
authors: Juan P
authors: JP
authors: Villabona-Monsalve
authors: Rosa E
authors: RE
authors: Islas
authors: William
authors: W
authors: Rodríguez-Córdoba
authors: Spiridoula
authors: S
authors: Matsika
authors: Jorge
authors: J
authors: Peón
mesh_terms: D000493:Allopurinol / Q000737:chemistry*; D004247:DNA / Q000737:chemistry*; D005453:Fluorescence; D011789:Quantum Theory
chemical_list: D000493:Allopurinol; D004247:DNA