Indigo is a commonly used dye over the years, ranging from the Ancient Mayan civilizations to modern day jean manufacturing. The dye has become of great interest to scientists because the dye has been able to resist fading over long time periods. Fading occurs because the molecules of certain pigments are less photostable and will decay when exposed to light.  Photostability is attributed to a molecule’s lifetime in the excited state. The shorter the lifetime, the less likely it will undergo a photochemical reaction, and the more photostable the molecule is. Therefore, what we want to know is what relaxation mechanism Indigo undergoes from its excited states that attributes to its short lifetime.  Currently, the most supported mechanism is a proton transfer between the nitrogen atom and the oxygen atom of the molecule. To test this, the amino hydrogens will be replaced with deuterium atoms. Pump-probe experiments will then be run to observe the new lifetimes of the deuterated indigo molecules. We expect to see an extended lifetime of these molecules because this suggests that Indigo does use a proton transfer to relax down from the excited state. A heavier molecule should move slower than a lighter one; therefore, during the transfer between the nitrogen and oxygen atoms, the deuterium should take longer to move through space, thus extending the time Indigo is in the excited state.