Luminescent properties of 2-mercaptobenzothiazolates of trivalent lanthanides

Abstract

A series of lanthanide complexes (Ln = Nd, Sm, Eu, Gd and Yb) with anionic 2-mercaptobenothiazolate (mbt) ligands were synthesized. Depending on the solvents chosen for the synthesis, Ln(mbt)₃(THF)₂ and Ln(mbt)₃(Et₂O) complexes were precipitated from THF and Et₂O solutions respectively. The structure of Yb(mbt)₃(Et₂O) was determined by X-ray analysis. Photophysical properties of the complexes were studied. It was found that under photoexcitation Nd and Yb derivatives exhibit bright metal-centered luminescence in the NIR region while Sm(mbt)₃(THF)₂ demonstrates intensive visible emission corresponding to ⁴G_5/2 → ⁶H_J (J = 5/2, 7/2, 9/2, 11/2) f–f transitions of Sm³⁺ along with NIR emission of moderate intensity. In the case of europium compounds as well as Sm(mbt)₃(Et₂O) no luminescence was detected. It is assumed that the difference in photoluminescence of Yb and Eu complexes can be explained by an intramolecular electron transfer process, which efficiently proceeds in these compounds.