Proton exchange is a very fast process and it is very difficult to study it. One can see the isotope effect only when the proton capture/dissociation occurs in a rate determining step. To my knowledge, there is no process where this occurs. The closest I can think of is pH jump experiment. Prepare a solution of the molecule in ionized state and give a sudden pH jump (towards low pH). The pH of the solution is instantaneously changed. The molecule reverts to the non-ionized state under these conditions.

People working with proteins perform deuterium exchange experiments. Protons belonging to ionizable groups of the residues present on the surface of the protein are exchanged very fast whereas the protons belonging to residues buried inside take time to exchange. This can be monitored by NMR.

I need to think if it is possible to study the isotope effect in a process where excited state proton transfer occurs or in a temperature jump experiment.

I have a paper in preparation were we report different fluorescence emissions depending on H/D isotope effects due to deuterated or non-deuterated solvent. The emission shift is rather small though and hardly seen by the naked eye.

Hi Matheus,

are You measuring the emission difference in a deuterated/non-deuterated solvent or do You add them as an additive? Please ellaborate on how You conduct the measurement itself.

For me the emission variation is visible after addition of ~1 eq of the Acetic acid (cyan emission)/Deuterated acetic acid to a solution of (yellow emission) my material in either DCM or CHCl3 (without acid they emit blue).