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

With ZnL1 or ZnL2 from the simple Salen-type Schiff-base ligand H2L1 (H2L1═N,N′-bis(3-methoxysalicylidene)-ethylene-1,2-diamine) or the carbazole-modified Salen-type Schiff-base ligand H2L2 (H2L2═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 (1LC and 3LC) of the ligand H2L1 or H2L2 and the effective energy transfer of Zn2+-Schiff-base (ZnL1 or ZnL2) to the Nd3+ 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 levelʹs match of the excited state of the chromophore to the Nd3+ ionʹs exciting state.