Speaker
Description
Ultrafast electronic relaxation of nucleobases from the 1ππ* state to the ground electronic state is crucial for the photostability of DNA and RNA. However, it has been suggested that electronic relaxation of pyrimidine nucleobases, nucleosides, and nucleotides in an aqueous environment generates an electronically-excited intermediate state with a lifetime of tens to hundreds of picoseconds with a relatively high quantum yield (QY) of 0.2–0.5. The generation of such a long-lived excited state seem to be inconsistent with the photostability of these molecules. We performed extreme ultraviolet time-resolved photoelectron spectroscopy and reinvestigated this problem and revealed that the accurately determined QY for long-lived excited states is much too low to allow an electronically excited reaction intermediate to exist. We investigated further the nature of the reaction intermediate using ultraviolet and infrared transient absorption spectroscopy, along with quantum chemical calculations to find that the intermediate is generated in the S0 state, and identified its structure.
