Effect of Tautomerization in the Photophysics of 5-(thiophen-2-yl)-6-aza Uracil

In this study, we calculated the vertical excitation energies (VEEs) and spin-orbit coupling constants (SOCs) of 5-(thiophen-2-yl)-6-aza uracil (TAU) and 2-methyl-5-(thiophen-2-yl)-6-aza uracil (MTAU) using ground-state optimized geometries in two solvents: acetonitrile and water. We then compared the theoretical and experimental absorption spectra for both modified 6-aza uracil derivatives in these solvents. Methylation is used to prevent the 3-enol/5-enol tautomerization observed in TAU and form the diketo tautomer. The aim is to determine if methylation can be used as an effective strategy to avoid tautomerization of TAU without affecting its photophysical properties. The experimental results and theoretical calculations demonstrated that the addition of a methylated group does not change the photophysical properties of the modified 6-Aza uracil.