Acyclic Ligands as Antenna Chromophores

9-Hydroxyphenalen-l-one (5) is a polycyclic P-diketone. A large ir-delocalization in 5 causes a remarkable red shift of the absorption bands, which can be exploited to achieve NIR lanthanide luminescence by visible light excitation with wavelengths up to 475 nm. 

NIR luminescence intensity for the Nd(III) or Yb(III) species. The most intense NIR emitting 8-hydroxyquinolinate lanthanide(III) complexes are the tetrakis complexes with 5,7-dihalo-8-hydroxyquinoline ligands. 

In order to obtain neutral tris complexes with the lanthanide(III) ion surrounded by three tridentate ligands to form a nine-coordinated geometry, an amide is introduced to the 2-position of 8-hydroxyquinoline, affording the tridentate derivatives 12,12-Br, and 12-Br2 [31]. In these tris complexes, the lanthanide(III) ion is shielded against intrusion by the solvent molecules into the first coordination sphere. As revealed by X-ray crystallography, the three stranded ligands coordinate to the lanthanide(III) ion in a helical fashion, leading to a coordination 

It appears that tetrapodal ligand 17 is an excellent sensitizer for the Yb(III) luminescence in water and a reasonable one for the Nd(III) emission. Methylation of the amide group eliminates the deactivation processes from the proximate N-H vibrations and increases both the lifetimes and quantum yields of the I7-CH3 complexes with the NIR emitting quantum yield being 0.04% for Nd(III), and 0.37% for Yb(III) species. Thus these molecular designs meet all the requirements for the development of NIR probes for bioanalyses. 

Functionalized organic dyes with polyaminocarboxylate have been widely utilized as feasible sensitizers to afford visible region excitation for sensitization of NIR lanthanide luminescence [36 5]. Verhoeven and coworkers [36, 37] first prepared a series of neodymium(III), erbium(III), and ytterbium(III) complexes with polyaminocarboxylate-functionalized fluorescein (21) and eosin (22) as sensitizing chromophores. These complexes show sensitized NIR 

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