Two highly photoluminescent Eu3+ β-diketonates complexes with ε-caprolactam as ancillary ligands: From synthesis to the first example as gunshot residue markers

This study reports the synthesis of two new Eu3+ β-diketonates and their complete experimental and theoretical spectroscopic characterizations. These compounds present [Eu(tta)3(ε-cap)(H2O)] 1 and [Eu(btfa)3(ε-cap)(H2O)] 2, supported by 4,4,4-trifluoro-1-(2-thienyl)-1,3-butanedione (Htta), 4,4,4-trifluoro-1-phenyl-1,3-butanedione (Hbtfa) formulas with a ε-caprolactam molecule acting as an ancillary ligand. These ligands act as efficient sensitizers for the Eu3+ ion, giving rise to an intense red emission. Due to this intense luminescence, compounds [Eu(tta)3(e-cap)(H2O)] 1 and [Eu(btfa)3(e-cap)(H2O)] 2 were selected as markers for the ammunition of a 38-caliber revolver and 0.380 pistol, respectively. This application is unprecedented for Eu3+ β-diketonates. The forensic assays indicated evident formation of luminescent gunshot residues (LGSR). Thus, these compounds may play an efficient role as allies in elucidating crimes.