Conferring phosphorogenic properties on iridium(III)-based bioorthogonal probes through modification with a nitrone unit

The use of bioorthogonal probes that display fluorogenic or phosphorogenic properties is advantageous to the labeling and imaging of biomolecules in live cells and organisms. Herein we present the design of three iridium(III) complexes containing a nitrone moiety as novel phosphorogenic bioorthogonal probes. These probes were non-emissive owing to isomerization of the C=N group but showed significant emission enhancement upon cycloaddition reaction with strained cyclooctynes. Interestingly, the connection of the nitrone ligand to the cationic iridium(III) center led to accelerated reaction kinetics. These nitrone complexes were also identified as phosphorogenic bioorthogonal labels and imaging reagents for cyclooctyne-modified proteins. These findings contribute to the development of phosphorogenic bioorthogonal probes and imaging reagents. Serving quench: The nitrone unit is utilized as both the emission quencher and bioorthogonal functional group in Ir^III complexes. Owing to isomerization of the C=N group these complexes are non-emissive but show emission turn-on upon cycloaddition with cyclooctynes. They were used as phosphorogenic bioconjugation reagents and bioorthogonal probes for live cells.