Hetero-binuclear near-infrared (NIR) luminescent Zn–Nd complexes self-assembled from the benzimidazole-based ligands

With the compound [Zn(HL1)2(Py)] (H2L1 = 2-(1H-benzo[d]imidazol-2-yl)-6-methoxyophenol), Py = pyridine) or [Zn(HL2)2(Py)] (H2L2 = 2-(1H-benzo[d]imidazol-2-yl)-4-bromo-6-methoxyphenol) as the precursor, complexes [ZnLn(HL1)2(Py)(NO3)3] (Ln = Nd, 1; Ln = Gd, 2) or [ZnLn(HL2)2(Py)(NO3)3] (Ln = Nd, 3; Ln = Gd, 4) were obtained by the further reaction with Ln(NO3)3·6H2O (Ln = Nd or Gd). The result of their photophysical properties shows that the strong and characteristic near-infrared (NIR) luminescence of Nd3+ ions for complexes 1 and 3 with emissive lifetimes in microsecond range, has been sensitized from the excited state (1LC and 3LC) of the benzimidazole-based ligands, and the involvement of heavy atoms (Br) at the ligand endows the enhanced NIR luminescent property.

Graphical abstractHetero-binuclear complexes [ZnLn(HL1)2(Py)(NO3)3] (Ln = Nd, 1; Ln = Gd, 2) and [ZnLn(HL2)2(Py)(NO3)3] (Ln = Nd, 3; Ln = Gd, 4) were obtained from two benzimidazole-based ligands H2L1 and H2L2, respectively. The sensitization and energy transfer for the NIR luminescence of the Nd3+ ions in the two Zn–Nd complexes (1 and 3) were discussed.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Hetero-binuclear Zn–Ln (Ln = Nd or Gd) arrayed complexes assembled from the benzimidazole-based ligands. ► Heavy-atom effect. ► Enhancement of near-infrared luminescent properties.