Study of energy transfer mechanism in the EuIII and GdIII homobimetallic complexes containing the anti-inflammatory drug naproxen and N,N-donors ligands

In this work, we present the synthesis, solid state characterization and complete photoluminescence study of new important homobimetallic lanthanide complexes containing the non-steroidal anti-inflammatory drug (NSAID) naproxen. The analytical and spectroscopic techniques reveals the formation of eight compounds of general formula [Ln(2)(nap)(6)(H2O)(4)] (Eu 1 and Gd 2), [Ln(2)(nap)(6)(bpy)(2)] (Eu 3 and Gd 4), [Ln(2)(nap)(6)(4,4'-dmbpy)(2)] (Eu 5 and Gd 6) and [Ln(2)(nap)(6)(phen)(2)] (Eu 7 and Gd 8), where: nap = naproxen ligand, bpy = 2,2'-bipyridine, 4,4'-dmbpy = 4,4'-dimethyl-2,2'-bipyridine and phen = 1,10-phenanthroline. Using the RM1 model, the molecular structures of the Eu-III complexes were calculated, with your optimized ground state geometries used to obtain all details involved in the energy transfer process. From the respective Gd-III complexes were obtained the lowest ligand triplet states, proving that the photoluminescence in the Eu-III naproxen complexes is proposed to be a ligand sensitized luminescence process. On the other hand, the position of the triplet states also explains the non-effective energy transfer in the Tb-III naproxen complexes. The presence of N,N-donors ligands (bpy, 4,4'-dmbpy and phen) results in an 3-4-fold increase in the quantum efficiency when compared with the Eu-III complex without nitrogen ligands. The high values of emission quantum efficiency (eta similar to 70 - 98%) show the Eu-III complexes can be potential candidates as emitters in biologic assays.