Laser Photodissociation Action Spectroscopy for the Wavelength-Dependent Evaluation of Photoligation Reactions

The nitrile imine-mediated tetrazole–ene cycloaddition is a widely used class of photoligation. Optimizing the reaction outcome requires detailed knowledge tetrazole photoactivation profile, which can only partially be ascertained from absorption spectroscopy, or otherwise involves laborious monitoring in solution. Photodissociation action spectroscopy (PDAS) combines advantages optical and mass spectrometry that events resulting change are recorded, thus revealing desired wavelength dependence product formation. Moreover, sensitivity selectivity afforded by spectrometer enable reliable assessment photodissociation profile even on small amounts crude material, accelerating design synthesis next-generation substrates. Using this workflow, we demonstrate onset for imine formation red-shifted ca. 50 nm with novel N-ethylcarbazole derivative relative to phenyl-substituted archetype. Benchmarked against solution-phase tunable laser experiments supported quantum chemical calculations, these discoveries PDAS powerful tool rapidly screening efficacy new substrates quest toward efficient visible light-triggered ligation biological applications.