Synthesis and Spectroscopic Studies on Azo-Dye Derivatives of Polymetallic Lanthanide Complexes: Using Diazotization to Link Metal Complexes Together

摘要

Lanthanide complexes have been widely used in a variety of imaging and assay related applications. In particular, gadolinium complexes have been used as contrast agents in magnetic resonance imaging, while luminescent lanthanide ions are widely used in bioassay and imaging. In such applications, it is important to be able to control the local environment around the metal and form kinetically stable complexes. For instance, in magnetic resonance imaging a complex should allow close approach and rapid exchange of water molecules, while retaining sufficient kinetic stability to be excreted intact. The case is altered for luminescence applications, since the excited states of lanthanide ions are quenched nonradia-tively by vibrational harmonics of the O-H oscillator and it is therefore desirable to exclude water molecules from the inner sphere. Since electric dipole f-f transitions are Laporte forbidden and have very low extinction coefficients, sensitizing chromophores are often incorporated into the ligand structure: these can sensitize emission from the lanthanide excited state and lead to dramatic enhancement of the emission from the metal center. Energy transfer from the chromophore to the metal is usually mediated via the chromophore triplet state, though other mechanisms have also been shown to be viable in some complexes.