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 UPE), U-PY-substituted duplexes do not show enhanced charge transfer (CT) emission quantum yields for duplexes with 5-fluorodeoxyuridine (U-F) electron traps near UPY compared to duplexes without traps. Furthermore, the average CT lifetime and emission quantum yield of UPY-substituted duplexes is independent of the U-F trap location. These new results strongly suggest that the excess electron in the PY center dot+/dU(center dot-) CT state of UPY is restrained from hopping to nearby UF traps due to attraction to PY center dot+.