Some spectral properties and luminescence intensities of Eu"' chelates with 4-(arylethynyl)pyridine-2,6-dicarboxylic acids 1-15 and 2,2',2",2"'-{[4-(arylethynyl)pyridine-2,6-diy~]bis(methy~enenitrilo)}tetrakis(acetic acids) 16-26 were measured both in H,O and EtOH solutions for the purpose of developing suitable labels to be used in time-resolved luminescence-based bioafinity assays (Tables I and2). The substitution at the Ar group has a significant effect upon the observed luminescence intensities, excitation wavelengths, and decay constants of the complexes. Moreover, the changes in the environment cause great variation in those properties of certain Eu"' chelates.
Introduction. -In recent years, a research effort was directed to luminescent lanthanide chelates to be used as labels in biological applications such as time-resolved luminescence immunoassays [ 11. The attention was focused on stable complexes containing a suitable aromatic ligand or conjugated system capable of transferring the excitation energy to the lanthanide ion by an internal energy-transfer process which causes a strong luminescence of the lanthanide ion.
It was reported that lanthanide cryptates are stable and efficient luminescent species [2]. In addition to them, luminescent polyaminopolycarboxylate chelates proved to be useful labels [3] [4]. In a previous paper, we reported the syntheses as well as some spectral and luminescent properties of the Eu'" chelates of the 4-(arylethynyl)pyridine-2,6-dicarboxylic acids 1-8 and the 2,2',2",2"'-([4-(arylethynyl)pyridine-2,6-diyl]bis(methylene-COOH COOH COOH COOH