Charge transfer excited-state dynamics in DNA duplexes substituted with an ethynylpyrenyldeoxyuridine electron source and a fluorodeoxyuridine electron trap

Studies of six 5-(pyren-1-yl-ethynyl)-2′-deoxyuridine (U PY)-substituted DNA duplexes in this work test and support the conclusions reported by Gaballah et al. (J. Phys. Chem. B 2005, 109, 5927-5934) based on investigations of 5-(2-pyren-1-yl-ethylenyl)-2′-deoxyuridine (U PE)-substituted DNA hairpins. As expected because of the rigid ethynyl linker in U PY (compared to the flexible ethylenyl linker in U PE), U PY-substituted duplexes do not show enhanced charge transfer (CT) emission quantum yields for duplexes with 5-fluorodeoxyuridine (U F) electron traps near U PY compared to duplexes without traps. Furthermore, the average CT lifetime and emission quantum yield of U PY-substituted duplexes is independent of the U F trap location. These new results strongly suggest that the excess electron in the PY ̇+/dU ̇- CT state of U PY is restrained from hopping to nearby U F traps due to attraction to PY ̇+. © 2005 American Chemical Society.