The proof-of-concept for conditionally activatable photocages is demonstrated on a new vinyltetrazine-derivatized coumarin. The tetrazine form is disabled in terms of light-induced cargo release, however, bioorthogonal transformation of the modulating tetrazine moiety results in fully restored photoresponsivity. Irradiation of such a “click-armed” photocage with blue light leads to fast and efficient release of a set of caged model species, conjugated via various linkages. Live-cell applicability of the concept was also demonstrated by the conditional release of a fluorogenic probe using mitochondrial pretargeting.

Fluorogenic probes efficiently reduce non-specific background signals, which often results in highly improved signal-to-noise ratios.

Easily accessible green-light activatable (>500 nm) photocages based on red-shifted, π-extended coumarin scaffolds are developed with uncaging efficiencies similar to those of recently introduced BODIPY derivatives. The photocages possess increased aqueous solubility, high absorption coefficients within the 450–600 nm range, and exceptionally high two-photon cross sections.

A series of double-fluorogenic siliconrhodamine-tetrazines were synthesized. One of these tetrazines is a membrane-permeant label allowing site-specific bioorthogonal tagging of intracellular proteins and super-resolution imaging.