The orthogonal reactivity of cysteines (Cys) under physiological conditions make them convenient residues for direct diversification of biomolecules. Of particular interest, Cys can be selectively modified with aryl moieties to functionalize peptides with a broad range of chemical groups through stable S-C(sp2) bonds. Among these reactions, Pd-mediated C-S cross-couplings and Pd(II) oxidative addition complexes (Pd-OACs) are of particular interest due to their chemoselectivity, high reactivity and compatibility with mild reaction conditions. In view of these properties, we envisioned that the design of Pd-OACs bearing small benzodiazole fluorogens could be employed for site-selective and minimal labeling of complex biomolecules. The late-stage labeling with benzodiazole fluorogens provides important advantages, including 1) the small size and neutral character of these fluorophores ensures minimal perturbation to preserve native cellular uptake, 2) their fluorogenic character enables both washfree and fluorescence lifetime imaging to feature the localization of peptides and proteins in subcellular structures (e.g., cell membrane, endosomes), and 3) the late-stage transfer of benzodiazole fluorophores via Cys-arylation results in chemically stable products.