Allosteric manipulation of photoexcited state relaxation in a series of RuII(bpy)2(bipyridine-crown ethers)

A series of ruthenium(II) crown ether complexes containing 4-, 5-, or 6-oxygen crowns tethered to a bipyridine at the 3,3' position were prepared and examined for their ability to act as luminescent sensors. The complexes [(bpy)(2)Ru(2,2'-bipyridine-3,3'-16-crown-4)](PF6)(2) and [(bpy)(2)Ru(2,2'-bipyridine-3,3'-19-crown-5)](PF6)(2) were characterized by X-ray crystallography. The 4-oxygen crown crystallizes in the P (1) over bar space group. The 5-oxygen crown crystallizes in the P (1) over bar space group. In both complexes, the inter-pyridine ring angle in the tethered bipyridine is twisted substantially away from 0degrees. Coordination of a heavy metal ion such as Pb2+ by the crown ether, and the geometric changes that result, were examined by UV/Vis, luminescence and NMR spectroscopy. The results show that there is a weak allosteric interaction between the Pb2+ ion and the Ru complexes, and that this interaction alters the luminescent behavior of the Ru complexes. (C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003.