Novel photoluminescent mesogenic Schiff-base ligands bearing [N4O4] donors and their bimetallic Zn(II) complexes

Novel photoluminescent salicylaldimine ligands condensed from 3/, 3/, 4/, 4/-tetraminobiphenyl and 4-substituted long alkoxy salicylaldehyde possessing two sets of tetradentate [N2O2] donor site and their binuclear zinc(II) complexes have been synthesized. The mesogenic and photophysical properties were investigated. The compounds were characterized by FT-IR, 1H and 13C NMR, UV–vis, elemental analyses, solution electrical conductivity measurements and FAB mass spectrometry. The mesomorphic behavior of these compounds was probed by differential scanning calorimetry and polarized optical microscopy. The ligand with six carbon chain length showed monotropic nematic mesomorphism at 128° C. However, the ligand with alkoxy tail of carbon length 12 showed enantiotropic SmC phase. The complexes are devoid of any mesomorphism. The low molar conductance values in CH2Cl2 indicate that the complexes are non-electrolytes. At 330 nm excitation, the ligand emits green light at ~ 516 nm (Φ = 30%) and ~ 549 nm (Φ = 16%) in solution and solid state, respectively. At similar excitation wavelength, the complexes exhibit blue light in solution at ~ 452 nm (Φ = 20%) and green light in solid state ~ 555 nm (Φ = 11%). The DFT calculations were performed using DMol3 program at BLYP/DNP level to ascertain the stable electronic structure of the complex.