We report a fast and highly efficient diazonium reaction that couples a nitroazobenzene chromophore to tyrosine and histidine residues, thus endowing peptides with high photoabsorption cross sections at 351 nm in the gas phase. Only the tagged peptides undergo ultraviolet photodissociation (UVPD) at 351 nm, as demonstrated for several Tyr- and His-containing peptides from protein digests. Additional selectivity is achieved by the integration of the UVPD-MS method with an in silico database search restricted to Tyr- and His-containing peptides. A modified MassMatrix algorithm condenses analysis by filtering the input database file to include Tyr/His-containing peptides only, thus reducing the search space and increasing confidence. In summary, derivatization of specific amino acid residues in conjunction with selective activation of the derivatized peptides provides a streamlined approach to shotgun proteomics.