With this objective in mind, our research group chose to investigate a modified 6-Aza Uracil derivative known as 5-(thiophen-2-yl)-6-Aza uracil (TAU )1-3 . During our study of its photophysical properties in aqueous solution, we observed 3-enol/5-enol tautomerization that affects the photophysical properties of the diketo tautomer of TAU that we are interested in using for further spectroscopic experiments . To address this, we decided to add a methyl group to the nitrogen at position N4, aiming to prevent tautomerization and thereby better analyze the photophysical characteristics of this molecule. The purpose is to investigate whether introducing a methyl group can serve as a practical and effective method to prevent the 3-enol/5enol tautomerization of TAU using theoretical calculations and steady-state experiments. This study aims to ensure that this modification does not adversely impact the molecule's photophysical properties, thus allowing us to investigate the diketo tautomer of TAU.