Synthesis, structure and near-infrared (NIR) luminescence of series of Zn2Ln (Ln = Nd, Yb or Er) complexes based on the Salen-type Schiff-base ligand with the flexible linker

With the Zn-Schiff-base [ZnL(CH3CN)] from the Salen-type Schiff-base ligand H2L (H2L = N,N′-bis(3-methoxy-salicylidene)cyclohexane-1,2-diamine) with the flexible linker as the precursor, a series of hetero-trinuclear Zn2Ln complexes [Zn2Ln(L)2(Cl)3] (Ln = Nd, 1; Ln = Yb, 2; Ln = Er, 3; Ln = Gd, 4) are obtained by the further reaction with LnCl3·6H2O, respectively. The results of their photophysical studies show that the strong and characteristic NIR luminescence with emissive lifetimes in the microsecond range, has been sensitized from the excited state (both 1LC and 3LC) of the ligand due to the effective intramolecular energy transfer.