Isotope effects in photochemistry: application to chromatic orthogonality.

The main challenge in developing new wavelength-specific photolabile protecting groups is the rigorous control of the photolysis rate. This rate is controlled by two factors: the chromophore absorbance and the reaction quantum yield. Fine-tuning the properties by changing substituents or structural features is difficult, because both factors are independently affected. By the use of the kinetic isotope effect, we could tune the quantum yield without altering the absorbance, and hence control the overall reaction rate. We exemplified this approach with chromatically orthogonally protected diesters.