A new class of discotic mesogens derived from Tris(N-salicylideneaniline)s existing in C3h and Cs keto-enamine forms

Two series of a unique class of columnar liquid crystals derived from tris(N-salicylideneaniline)s [TSANs] in which the proton and the electron interact with each other through the H-bonding environment are reported. The synthesis is carried out by condensing 1,3,5-triformylphloroglucinol with the respective dialkoxyanilines or trialkoxyanilines. H-1 NMR and H-1-H-1 COSY NMR studies revealed their existence as an inseparable mixture of two keto-enamine tautomeric forms with C-3h and C-s rotational symmetries instead of the expected enol-imine form. The influence of the number of peripheral alkoxy tails on the columnar mesomorphic behavior is investigated by using polarizing optical microscopy, differential scanning calorimetry, and X-ray scattering. The fluid/glassy columnar states probed for a number of representative compounds confirmed the D-6h (hexagonal) or D-2h (rectangular) symmetry of the columns. The electronic absorption and emission characteristics of these compounds have been studied in both mesomorphic and solution states. Of special interest, the photoluminescence spectra of solution and fluid/ glassy two-dimensional structure evidently disclose the promising light generating capability of these new discotics systems.