Liquid crystalline 1,3,5-triazines incorporating rod-like azobenzene sub-units

New liquid crystalline 1,3,5-triazines are presented that incorporate three mesogenic groups based on rod-like azobenzene moieties. The synthesis was carried out by reaction of cyanuric chloride with 4-alkoxy-4-aminoazobenzene derivatives. The mesomorphic behaviour was investigated by polarizing microscopy, differential scanning calorimetry and X-ray scattering. Besides a nematic and a SmA phase, the trisazomelamines form a higher ordered mesophase within a broad temperature range below the smectic A phase. With respect to the rod-like azobenzene sub-units, the low temperature phases display a smectic 'bilayer' structure. The molecules are antiparallel aligned within one layer. Furthermore, 1,3,5-triazines incorporating just two azobenzene groups are presented, these were prepared to investigate the influence of the number of rod-like sub-units linked to the triazine core on the mesomorphic properties.