Evaluation of solution structures of highly luminescent europium(III) chelates by using laser induced excitation of the [formula omitted] transition

Abstract

Solution structures of 13 Eu(III) chelates were examined by using laser induced excitation of the 7 F 0 → 5 D 0 transition. Remarkable variations in the 7 F 0 → 5 D 0 excitation spectra of 2,2′,2″,2″−{[aryl]bis(methylenenitrilo}tetrakis(acetic acid) complexes of Eu(III) are observed depending on the denticity of the ligand and the number and character of the coordinated nitrogen atoms. The evaluation of the structures is made on the basis of the energy of the 7 F 0 → 5 D o excitation transition of Eu(III) because the 7 F 0 → 5 D 0 transition energy is dependent on the number and type of coordinating atoms in the first coordination sphere of Eu(III). Additional information about the structures is obtained by measuring the excited-state lifetimes of the Eu(III) chelates. The 7 F 0 → 5 D 0 transition energy shifts always an equal amount to lower energies due to the coordination of a certain group or atom. The energies of the 7 F 0 → 5 D 0 excitation transitions are also used to calculate these ‘nephelauxetic’ shift parameters for coordinated nitrogen heteroatoms iin the 2,2′,2″,2″−{[4-phenylethynyl)pyridine-2,6-diyl]bis (methylenenurido)}tetrakis(acetic acid) ( 3). 2,2′,2″,2″-[(2,2′-bipyridine-6,6′-diyl)bis-(methylenenitrilo)] tetrakis (acetic acid) ( 4). 2,2′,2″,2″-[(2,2′:6,2″-terpyridine-6,6″-terpyridine-6.6″-diyl)bis(methylenenitrilo)]tetrakis(acetic acid) ( 5), 2,2′,2″,2″- (pyrazole-1,3-diyl)-bis(pyridine)-2,2′-diyl]bis(methylenenitrilo)]tetrakis(acetic acid) ( 7). 2,2′,2″,2″-([thizole-2,4-diyl)bis(pyridine)- 2,2′-diyl]-bis(methylenenitrilo(]tetrakis(acetic acid) ( 8) and 2,2′,2″,2″-([2,2,′-pyridine-2,6-diyl)bis(thiazole)-4,4′-diyl]bis-(methylenenitrilo)]-tetrakis(acetic acid) ( 9) complexes. The variation in the shift parameters of the nitrogen heteroatoms is suggested to be due to the different distances between the nitrogen heteroatoms and Eu(III) ions.