Hetero-trinuclear near-infrared (NIR) luminescent Zn2Ln complexes from Salen-type Schiff-base ligands

Abstract

With the Zn-Schiff-base [ZnL 1 (Py)] or [ZnL 2 (Py)] from the simple Salen-type Schiff-base ligand H 2 L 1 or H 2 L 2 (H 2 L 1 : N,N 0 -bis(salicylidene)ethylene-1,2-diamine; H 2 L 2 : N,N 0bis(salicylidene)phenylene-1,2-diamine) without the outer O 2 O 2 portion as the precursor, two series of eight trinuclear Zn 2 Ln arrayed complexes (Ln = Nd (1 or 5), Yb (2 or 6), Er (3 or 7) or Gd (4 or 8)) have been obtained by the further reaction with Ln(NO 3 ) 3 Á6H 2 O, respectively. The results of photophysical studies show that the strong and characteristic NIR luminescence with emissive lifetimes in microsecond ranges, has been sensitized from the excited state ( 1 LC and 3 LC or only 1 LC) of the ligand, whereas the Zn(II)-based visible luminescence is mostly quenched because of quite effective intramolecular energy transfer from the ligand-centered excited state of the Zn(II)-Schiff base complex to Ln(III) ions.

Terbium sensitized luminescence for the determination of fexofenadine in pharmaceutical formulations

“…Many multinuclear heterometallic 3d-4f complexes were reported (Towatari et al, 2013;Lu¨et al, 2010;Yang et al, 2005;Bi et al, 2009). The formation of these complexes was evidenced by characterization by X-ray crystallography which revealed the existence of functional bridge in these 3d-4f complexes.…”

“…The donation of OH groups was the main facilitator of the formation of such complexes. In the coordination compounds involving Zn 2+ and lanthanide ions, it was reported that complexation of a pyridine group to Zn 2+ ions in these complexes resulted in congestion around the coordination sphere of the 4f Ln 3+ ions (Bi et al, 2009). This has led to a significant minimization of the luminescence quenching from solvents molecules around the lanthanide ions.…”

Hetero-binuclear near-infrared (NIR) luminescent ZnLn (Ln = Nd, Yb or Er) complexes self-assembled from the benzimidazole-based ligand

“…On the other hand, based on the typical Salen-type Schiff-base ligands without the outer O 2 O 2 moieties from MeO groups, series of NIR luminescent Zn 2 Ln (Ln = Nd, Yb or Er) arrayed complexes have been obtained [9], in which from the viewpoint of enhancement of NIR luminescent properties, the use of the flexible linker while not the rigid one of the typical Salen-type Schiff-base ligands without the outer O 2 O 2 moieties, could improve the NIR luminescent quantum efficiency due to the effective intramolecular energy transfer from the ligand-centered 3 LC and 1 LC not just 1 LC excited state to the Ln 3 + ions. Moreover, the occupation of pyridine at the axial position of the Zn 2 + ion, is helpful for the strong NIR luminescence, which should be due to the complete avoidance of the luminescent quenching effect arising from OH-, CH-or NH-oscillators around the Ln 3+ ion.…”

Mixed anion-induced Salen-based Zn2Ln3 (Ln=Nd, Yb or Er) complexes with near-infrared (NIR) luminescent properties

“…In the dilute MeCN solution at 77 K, complex 5 displays both the stronger ligand fluorescence (λ em = 462 nm and τ = 1.20 ns) and the strong ligand phosphorescence (λ em = 497 nm and τ = 4.21 ms), which shows that the sensitization of the NIR luminescence for complexes 2-4 should arise from both the 1 LC and 3 LC excited states of the Salen-type Schiff-base ligand H 2 L at low temperature [29]. If the antenna luminescence lifetime of complex 5 is to represent the excited-state lifetime in the absence of the energy transfer, the energy transfer rate (k ET ) in the complexes 2-4 can thus be calculated from k ET = 1/τ q − 1/τ u [30], where τ q is the residual fluorescence lifetime, and τ u is the weakened while unquenched fluorescence lifetime in the reference complex 5, so the energy transfer rates for the Nd 3+ , Yb 3+ and Er 3+ ions in complexes 2-4 may all be estimated to be above 1.2 × 10 8 s −1 .…”