A combined femtosecond fluorescence and TD-DFT study of uracil derivatives in aqueous solution

Abstract

This chapter provides several interesting indications on the excited-state behavior of uracil derivatives in aqueous solution. The excited-state lifetimes of all the compounds examined, except 5-fluoro uracil, are dominated by a component shorter than 250 femtosecond. Calculations indicate that the relevant state for discussing the absorption and fluorescence spectra of uracil derivatives in aqueous solution is the ππ*. The key steps in the ultrafast internal conversion are the pyramidalization of C5 and the out of plane motion of C5 substituent, which explains why the excited-state lifetime depends mainly on the nature of the C5 substituent. The shape of the potential energy surface of the S1 electronic states seems consistent with a very fast nonradiative decay. The result strongly supports the reliability of the general picture of the ultrafast ground state recovery of excited uracils in aqueous solution.