Isotope Effects in Photochemistry: Application to Chromatic Orthogonality
摘要:
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.
Isotope Effects in Photochemistry. 1. o-Nitrobenzyl Alcohol Derivatives
摘要:
The photolysis of o-nitrobenzyl alcohol derivatives shows a strong kinetic isotope effect (KIE up to 8.3) at the benzylic center. For some derivatives, the KIE is wavelength dependent, suggesting the involvement of higher excited states. In addition to the important mechanistic consequences, isotopic substitution is a convenient way to alter the quantum yield without changing the absorbance, as would the introduction of substituents. This paves the way for a subtle tuning of the reaction rates in photochemical reactions. We illustrated this feature in the sequential deprotection of a diester protected at both termini with photolabile groups.