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

Abstract

Abstract With the binuclear Zn 2 L ([Zn 2 L(OAc) 2 (H 2 O)], 1 ) compound from the Salen-type Schiff-base ligand H 2 L (H 2 L: N,N′-bis(salicylidene)cyclohexane-1,2-diamine) with the flexible linker as the precursor, a series of hetero-trinuclear Zn 2 Ln complexes (Ln = Nd ( 2 ), Ln = Yb ( 3 ), Ln = Er ( 4 ) or Ln = Gd ( 5 )) have been obtained by further reaction with Ln(OAc) 3 ·6H 2 O. 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 ( 1 LC and 3 LC) 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 Ln 3 + ion for the larger conjugation effect, endowing the energy level's good match between the excited state ( 3 LC) of the chromophore to the corresponding Ln 3 + ion's exciting state, results in the enhancement of their NIR luminescence.