Comparison of Py•+/dU•- charge transfer state dynamics in 5-(1-pyreny1)-2′-deoxyuridine nucleoside conjugates with amido-, ethylenyl-, and ethynyl linkers

Femtosecond, picosecond, and nanosecond transient absorbance (TA) and picosecond emission kinetics results are presented for three 5-(1-pyrenyl)-2'-deoxyuridine nucleosides each with a different two-atom linker joining pyrenyl C-I to uracil C-5. The linkers are respectively -NHCO-, -(CH2)(2)-, and -C C- for PAdU, PEdU, and PYdU. For all three nucleoside conjugates, most conformers undergo intramolecular charge transfer (CT) from their pyrenyl (1)(pi,pi*) excited states to form Py.+/dU(.-) CT products in ultrashort times: <= 0.6 ps for PAdU <= 30 ps for PEdU, and <= 100 ps for PYdU (instrumentally limited times). Additionally for all three nucleosides, a small fraction of conformers also undergoes slower intramolecular CT from their pyrenyl (1)(pi,pi*) states in times as long as tens of nanoseconds. Importantly, for use of these nucleosides in studies of excess electron transport in DNA, the lifetimes the CT products in MeOH lengthen significantly in the above series: 6.0 ps for PAdU, 560 ps for PEdU (the shortest of three TA lifetime components), and 1.06 ns for PYdU. The effects on pyrenyl-dU nucleoside CT state dynamics due to adding oxygen via both aeration and oxygen saturation are also examined for the PEdU nucleoside in MeOH.