Photo-luminescent hetero-trinuclear Zn2Ln (Ln = Nd, Yb, Er or Gd) complexes based on the binuclear Zn2L precursor

With the binuclear Zn2L ([Zn2L(OAc)2(H2O)], 1) compound from the Salen-type Schiff-base ligand H2L (H2L: N,N′-bis(salicylidene)cyclohexane-1,2-diamine) with the flexible linker as the precursor, a series of hetero-trinuclear Zn2Ln complexes (Ln = Nd (2), Ln = Yb (3), Ln = Er (4) or Ln = Gd (5)) have been obtained by further reaction with Ln(OAc)3·6H2O. The result of their photophysical properties shows that the strong and characteristic NIR luminescence with emissive lifetimes in the ranges of microseconds for each of the complexes 2–4, has been sensitized from the excited state (1LC and 3LC) of the Salen-type Schiff-base ligand with the flexible linker. Especially, the almost planar arrangement of two energy donors of ZnL components around the Ln3 + ion for the larger conjugation effect, endowing the energy levelʹs good match between the excited state (3LC) of the chromophore to the corresponding Ln3 + ionʹs exciting state, results in the enhancement of their NIR luminescence.