Photophysics of Nitro-Substituted Unnatural Nucleic Acid Base.

The unnatural nucleic acid base (uNAB), 6-amino-3-methyl-5-nitropyridin-2(1H)one, often referred to as can form a base pair with the uNAB 2-aminoimidazo[1,2-]-1,3,5-triazin-4(8H)-one (referred to as P) and is analogous to a guanine-cytosine (G-C) pair. However, it is well-known that the nonradiative decay pathway of the P-Z pair is significantly different from that of the G-C pair (Cui et al., , , 605117-605125). In this work, we study the excited state processes in using state-of-the-art multireference methods and dynamical techniques to ascertain the predominant nonradiative channels. We find that unlike in the natural NABs, the excited state processes in are driven primarily by the -NO group rotation. The electron-withdrawing effect of the -NO substituent plays a crucial role. We further ascertained that ultrafast deactivation channels are possible in and identified the stationary point geometries that are responsible for these channels.