Photophysics of the lanthanide complexes with conjugated carboxylic acids by low temperature fluorescent spectroscopy.

In the context, some lanthanide (Eu(3+), Tb(3+) and Sm(3+)) complexes with conjugated carboxylic acids (pyridine-carboxylic acids derivatives) have been synthesized and characterized. The low temperature fluorescent spectra for these complexes have been measured at nitrogen atmosphere (77 K), indicating that the central Ln(3+) ions locate in an equivalent coordination environment with low symmetry for most of these lanthanide complexes belonging to dimeric or polymeric structure. Therefore, the electronic dipole transition (supersensitive transition) ((5)D(0) --> (7)F(2) for Eu(3+), (5)D(4) --> (7)F(6) for Tb(3+), (4)G(5/2) --> (6)H(9/2) for Sm(3+)) and magnetic dipole transition ((5)D(0) --> (7)F(1) for Eu(3+), (5)D(4) --> (7)F(5) for Tb(3+), (4)G(5/2) --> (6)H(5/2) for Sm(3+)) show the regular change in the corresponding split number of fluorescent spectra, which can be realized to predict the fine structure of lanthanide complexes.