Charge Transfer Excited-State Dynamics in DNA Duplexes Substituted with an Ethynylpyrenyldeoxyuridine Electron Source and a Fluorodeoxyuridine Electron Trap

Abstract

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*+.