Synthesis and spectral characterization of a long-lifetime osmium (II) metal-ligand complex: a conjugatable red dye for applications in biophysics

There is a need for luminescent probes, which display both long excitation and emission wavelengths and long decay times. We synthesized and character ized an osmium metal-ligand complex which displays a mean decay time of ove r 100 ns when bound to proteins. [Os(1,10-phenanthroline)(2)(5-amino-1,10-p henanthroline)](PF6)(2) can be excited at wavelengths up to 650 nm, and dis plays an emission maximum near 700 nm. The probe displays a modest but usef ul maximum fundamental anisotropy near 0.1 for 488-nm excitation, and thus convenient when using an argon ion laser. [Os(phen)(2)(aphen)](PF6)(2) is r eadily activated to the isothiocyanate for coupling to proteins. When coval ently linked to bovine serum albumin the intensity decay is moderately hete rogeneous with a mean decay time of 145 ns. The: anisotropy decay of the la beled protein displays a correlation time near 40 ns. This relatively long lifetime luminophores can be useful as a biophysical probe or in clinical a pplications such as fluorescence polarization immunoassays, (C) 1999 Publis hed by Elsevier Science B.V. All rights reserved.