Hetero-trinuclear near-infrared (NIR) luminescent ZnLn2 (Ln = Nd, Yb or Er) complexes based on monomer ZnL Schiff-base precursor and o-vanillin

With the monomer [Zn(L1)(H2O)] (1) complex in situ formed by the deprotonated hexadentate Salen-type Schiff-base ligand H2L1 (H2L1 = N,N′-bis(3-methoxy-salicylidene)cyclohexane-1,2-diamine) and Zn(NO3)2 as the precursor, series of the hetero-trinuclear ZnLn2 complexes [ZnLn2(L1)2(L2)(NO3)2Cl] (Ln = Nd, 2; Ln = Yb, 3; Ln = Er, 4 or Ln = Gd, 5) were obtained from the further reaction with LnCl3 (Ln = Nd, Yb Er or Gd) and the second o-vanillin (HL2) ligand, respectively. The photophysical properties of complexes 2–4 showed that the characteristic near-infrared (NIR) luminescence of Ln3 + ions with two emission centers and emissive lifetimes in microsecond ranges, was sensitized from the excited state (both 1LC and 3LC) of mixed H2L1–HL2 ligands.