Effective enhancement of near-infrared emission by carbazole modification in the Zn–Nd bimetallic Schiff-base complexes

Abstract

With ZnL 1 or ZnL 2 from the simple Salen-type Schiff-base ligand H 2 L 1 (H 2 L 1 ═N,N′-bis(3-methoxysalicylidene)-ethylene-1,2-diamine) or the carbazole-modified Salen-type Schiff-base ligand H 2 L 2 (H 2 L 2 ═N,N′-bis(3-methoxy-5-{2-[4-(N-carbazyl)-phenyl]-ethynyl}-ethylene-1,2-diamine) as the precursor, two series of four bimetallic ZnLn complexes (Ln=Nd(1 or 3), Ln=Gd (2 or 4) are obtained, respectively. The photophysical properties results showed that the sensitization from the excited state ( 1 LC and 3 LC) of the ligand H 2 L 1 or H 2 L 2 and the effective energy transfer of Zn 2+ -Schiff-base (ZnL 1 or ZnL 2 ) to the Nd 3+ ion for the NIR luminescence were realized, respectively. Especially through the cabarzole modification, the improved NIR luminescence of the ZnNd complex 3 was observed due to the realization of the energy level's match of the excited state of the chromophore to the Nd 3+ ion's exciting state. In the Zn–Nd Schiff-base complexes from H 2 L 1 or the carbazole-modified H 2 L 2 , through the carbazole modification, the improved NIR luminescence of the ZnNd complex 3 was observed, due to the avoiding of the luminescent quenching effect arising from OH-, CH- or NH-oscillators of the solvates around the Nd 3+ ion in combination with the realization of the energy level's match of the excited state of the chromophore to the Nd 3+ ion's exciting state. ► Carbazole-modified Salen-type Schiff-base ligand. ► Effective sensitization and efficient energy transfer. ► Enhancement of near-infrared luminescence of the Zn–Nd binuclear Schiff-base complexes.