Abstract
Mesomorphism induced by metal (VO2+, Ni2+, Cu2+ and Zn2+) coordination and its influence on the photophysical properties of a new series of symmetric “salphen”‐type N,N‐bis(4‐n‐alkoxysalicylidene)‐4,5‐dichloro‐1,2‐phenylenediamine ligands (n = 12, 14, 16) bearing highly electronegative spacer substituents and alkoxy arms of varied length have been investigated. The mesomorphism has been probed by polarizing optical microscopy (POM), differential scanning calorimetry (DSC), and variable‐temperature powder X‐ray diffraction (XRD). The Schiff base ligands are non‐mesomorphic; however, coordination to NiII and ZnII ions induces columnar mesomorphism, this being stable down to room temperature in the latter case. Interestingly, the complexes of CuII and VOIV did not show any mesomorphism. The free ligands and the ZnII complexes are luminescent both in the condensed state and in solution, with emission maxima in the condensed state being significantly red‐shifted with respect to those in solution. The energy‐optimized structure of a representative ZnII complex was ascertained to be distorted square planar in a DFT study employing the GAUSSIAN 09 program. The ZnII and VOIV complexes exhibited solvatochromic effects, showing interesting aggregation behavior in the former case.
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