Zinc(II)-salphen complexes bearing long alkoxy side arms: Synthesis, solvent dependent aggregation, and spacer group substituent effect on mesomorphism and photophysical property

Hemi-disc shaped zinc(II) complexes of two new series of halogen-substituted `salphen' type Schiff base ligands [ZnL]; H2L = [N,N'-Bis(4-n-alkoxysalicylidene)-4-fluoro/bromo-1,2-diaminobenzene] (n = 12, 14, 16) have been synthesized and their mesomorphism and photophysical properties investigated. The ligands and zinc(II) complexes displayed columnar mesophases over a much wider temperature range. Depending on the halogen substitution at the ligand's spacer; different variant of columnar phases were exhibited by the ligands and the zinc(II) complexes. The ligands and the complexes displayed fluorescence at ambient temperature in the bluegreen region with moderate to low intensity. Density functional theory (DFF) calculations indicated a distorted square-planar geometry around the zinc(II) center in the complexes. The coordinative unsaturation of the zinc(II) center in these complexes leads to interesting aggregation properties in a dilute solution of non-coordinating solvents. However, in coordinating solvent, axial coordination to the zinc(II) ion occurred leading to complete de-aggregation to monomer. (C) 2017 Elsevier B.V. All rights reserved.