Photo-luminescent hetero-tetranuclear Zn2Ln2 (Ln = Nd, Yb, Er, Gd, Eu or Tb) complexes self-assembled from the benzimidazole-based HL and bpe

Abstract

Through the self-assembly of the benzimidazole-based ligand HL ( HL = 2-(1H-benzo[d]imidazol-2-yl)-6-methoxyohenol) with Zn(OAc) 2 , Ln(NO 3 ) 3 (Ln = Nd, Yb, Er, Gd, Eu or Tb) and bpe (bpe = trans -bis(4-pyridyl)ethylene), six hetero-tetranuclear Zn 2 Ln 2 -arrayed complexes (Ln = Nd, 1 ; Yb, 2 ; Er, 3 ; Gd, 4 ; Eu 5 ; or Tb, 6 ) are obtained, respectively. The result of their photophysical properties shows that the characteristic near-infrared (NIR) luminescence of Nd 3 + , Yb 3 + or Er 3 + ions and visible luminescence of Tb 3 + ions with emissive lifetimes in microsecond ranges have been sensitized from the excited states ( 1 LC and 3 LC) of the benzimidazole-based ligand, while due to the charge-transfer process from the ligand excited state to the Eu 3 + ions, the Eu 3 + -based emissions are quenched in complex 5 . Series of hetero-tetranuclear Zn 2 Ln 2 complexes [Zn 2 Ln 2 (L) 4 (bpe)(NO 3 ) 6 ] (Ln = Nd, 1 ; Yb, 2 ; Er, 3 ; Gd, 4 ; Eu 5 ; or Tb, 6 ) were synthesized and characterized. Their photophysical properties show that the characteristic near-infrared (NIR) emissions of Nd 3 + , Yb 3 + and Er 3 + ions for 1 – 3 + and visible emissions of Tb 3 + ion for 6 are sensitized from the excited states ( 1 LC and 3 LC) of the mixed ligands, while the Eu 3 + -based emissions are quenched in 5 due to charge-transfer process. • Zn 2 Ln 2 -arrayed complexes from the benzimidazole-based ligand • Sensitization and energy transfer • Energy level match and charge transfer