Photophysics of the triple state of metal complexes of 9-anthracenecarboxylic acid

The triplet-triplet (T-T) absorption spectra and the T-T absorption decay kinetics are measured for solutions of 9-anthracenecarboxylic acid (ACA) and its complexes with metal ions (Cd³⁺ and Ln³⁺=Y³⁺, La³⁺, Ce³⁺, Eu³⁺, Gd³⁺, and Tb³⁺) in dimethylsulfoxide (DMSO) by the methods of flashlamp and laser pulse photolysis. The rate constants k _T of intracomplex quenching of the triplet state are measured for ACA complexes with ions Gd³⁺, Ce³⁺, Tb³⁺, and Eu³⁺. Larger values of k _T in complexes of ACA with paramagnetic ions Ce³⁺, Tb³⁺, and Eu³⁺, which have low-lying energy levels, compared to the values of k _T for complexes with other ligands (pyrene-3-sulfonate, pyrene-1,3,6,8-tetrasulfonate, and benzoghi]perylene-1,2-dicarboxylate) were explained by the lower energy of the triplet state of ACA (14400 cm^?1). For a complex with a paramagnetic ion Gd³⁺, which has no low-lying energy levels, the value of k _T is close to that measured by us earlier for the inner-sphere complex of pyrene-1,3,6,8-tetrasulfonate with the same ion. These results confirm our earlier assumption about the inner-sphere complexing of ACA with Ln³⁺ ions in DMSO.