AbstractIn view of the fact that many transition metal complexes display intense and long‐lived metal‐to‐ligand charge‐transfer emission with a large Stokes' shift, we have incorporated biotin into a series of luminescent rhenium(I), iridium(III) and ruthenium(II) polypyridine complexes to form new probes for the protein avidin. All these luminescent transition metal polypyridine biotin complexes displayed enhanced emission intensities and extended lifetimes upon binding to avidin. These changes are closely related to the hydrophobic biotin‐binding pockets of avidin and the increased rigidity of the local environment of the probes after they bind to the protein. We have exploited the characteristics of these luminescent transition metal biotin complexes in the development of vario