Novel rhenium(I) polypyridine biotin complexes that show luminescence enhancement and lifetime elongation upon binding to avidin.

While most biotin-fluorophore conjugates suffer from significant emission quenching upon binding to avidin due to resonance energy-transfer, three novel rhenium(I) polypyridine biotin complexes have been designed in view of their characteristic photophysical properties, in particular their large Stokes shifts. In contrast to most biotin-fluorophore conjugates, the (3)MLCT emission intensities and lifetimes of these rhenium(I) complexes are increased upon binding to avidin, rendering them luminescent probes for avidin and biotinylated species.