Indigo is a historically important dye, due to its bright color and availability all around the world. Indigo is important due to its resistance to fading after prolonged exposure to light. The excited state dynamics of indigo is being studied to understand the photostability of the molecule. Indigo is believed to have an excited state intramolecular proton transfer (ESIPT) relaxation mechanism which makes it so highly photostable. Therefore, we want to investigate the excited state lifetime of indigo and the relaxation mechanism that indigo undergoes. Our goal is to exchange the hydrogen atoms with deuterium atoms. With deuteration, we hypothesize that indigo will take longer to relax. This study will provide important results of the relaxation mechanisms of indigo.