Near infrared luminescent hexanuclear zinc–lanthanide prisms: Synthesis, structure and luminescent properties

The use of the Schiff-base ligand N,N′-bis(3-methoxysalicylidene)ethylene-1,2-diamine (H2L) and fumarate (fum) enables the construction of the hexanuclear luminescent Zn–Ln complexes [Zn4Ln2L4(fum)2] (NO3)2·3CH3OH (Ln = Nd 1; Yb 2; Er 3; Gd 4). The complexes have been characterized by elemental analysis, FT-IR spectra and ESI mass spectrometer. The single crystal X-ray crystallographic study has been carried out on 1. Luminescent properties of these complexes including UV–Vis absorption spectra, excitation, visible and NIR region emission spectra, and NIR emission lifetime have been determined. The intrinsic near-infrared luminescent quantum yield of 1 and 2 are estimated to be 0.63% and 0.84% calculated from the observed lifetime and the natural lifetime of the lanthanide ions, respectively. Systematic analysis suggests that enhancement of near infrared emission could be observed upon construction of the stable polynuclear structures.