A Comparative Picosecond Transient Infrared Study of 1-Methylcytosine and 5′-dCMP That Sheds Further Light on the Excited States of Cytosine Derivatives

The role of N1-substitution in controlling the deactivation processes in photoexcited cytosine derivatives has been explored using picosecond time-resolved IR spectroscopy. The simplest N1-substituted derivative, 1-methyl-cytosine, exhibits relaxation dynamics similar to the cytosine nucleobase and distinct from the biologically relevant nucleotide and nucleoside analogues, which have longer-lived excited-state intermediates. It is suggested that this is the case because the sugar group either facilitates access to the long-lived (1)n(O)pi* state or retards its crossover to the ground state.