Conformational Control of Excited-State Dynamics in Highly Distorted Ru(II) Polypyridyl Complexes

• Published in: Inorganic chemistry 2005-05, Vol.44 (11), p.4066-4076
• Main Authors: McFarland, Sherri A, Magde, Douglas, Finney, Nathaniel S
• Format: Article
• Language: English
• ISSN: 0020-1669; 1520-510X
• DOI: 10.1021/ic0502729

Tris(bipyridyl)ruthenium(II) complexes modified such that one of the bipyridines is appended with a crown ether display luminescence that is responsive to complexation with metal ions. The parent species, Ru(bpy)3 2+, is moderately luminescent, with an emission lifetime of about 1 μs in fluid solution at room temperature. The modified complexes are much less emissive, with lifetimes near 1 ns. Conformational flexibility and distortion in the crown-ether complexes enhance nonradiative decay. Noncovalent binding of metal ions, however, restores luminescence intensity by reducing nonradiative decay and increasing the lifetime 10- to 100-fold. Reported here are the syntheses and steady-state and time-resolved luminescence measurements in addition to other supporting spectroscopic characterization. Seven metals were investigated; significant luminescence enhancements occur in the presence of Mg2+, Ca2+, and Pb2+. Effective concentrations of metal ions range from tens of μM to hundreds of mM. The steady-state enhancements are readily measured, but they are less than would be expected from the lifetime changes, partly because only a portion (not more than 50%) of the fast (1 ns) decay in Ru(bpy)2(bpy-crown) is capable of converting to the conformation possessing the longer lifetime. A photophysical model is proposed to explain these and other observations.