Near-infrared (NIR) luminescent hetero-tetranuclear Zn2Ln2 (Ln = Nd, Yb or Er) complexes self-assembled from the benzimidazole-based HL and two rigid 4,4′-bipyridine ligands with different spacers

Through the self-assembly of the benzimidazole-based ligand HL (HL = 2-(1H-benzo[d]imidazol-2-y1)-6methoxyphenol) with zo(oAc)2.2H20, Ln(NO3)(3.6)H2O (Ln = Nd, Yb, Er or Gd) and 4,4'-bipyridine ligand (bpy, 4,4'-bipyridine or bpe, trans-bis(4-pyridyl)ethylene), two series of Zn2Ln2-arrayed complexes [Zn(2)Ln(2)(L)4(bPY)(NO3)6I (Ln = Nd, I; Yb, 2; Er, 3 or Gd, 4) and [2n(2)Ln(2)(L)4(bpe)(NO3)61 (Ln = Nd, 5; Yb, 6; Er, 7 or Gd, 8) were obtained, respectively. The result of their photophysical properties shows that the characteristic near-infrared (NIR) luminescence of Nd3+, Yb3+ or Er3+ ion has been sensitized from the excited state (both 1LC and 3LC) of the mixed HL and bipyridyl ligands in both complexes 1-3 and 5-7. Moreover, the change from bpy to bpe bridging for the fine-tuning of whole molecular conjugations, attributing to the different crossings of the two benzimidazole-based L ligands, has the important influence on their NIR luminescent properties. (C) 2013 Elsevier B.V. All rights reserved.