Influence of spacer chain lengths and polar terminal groups on the mesomorphic properties of tethered 5-phenylpyrimidines

Based on 5-(4-hydroxyphenyl)-2-octylpyrimidine 8, 5-phenylpyrimidine derivatives 3 -7, 9 with different spacer chain lengths (C-2 up to C-6) and different terminal polar groups (Br, Cl, N-3, OH, CN) were synthesized by etherification and nucleophilic substitution. The mesomorphic behaviour of these compounds was investigated by differential scanning calorimetry (DSC), polarizing optical microscopy (POM) and X-ray diffraction (WAXS and SAXS) and revealed smectic A mesophases for bromides, chlorides and azides 3, 4 and 6. For these compounds a maximum phase width was observed for the C-5 spacer regardless of the terminal group, whereas the hydroxy-and cyano-substituted derivatives 5 and 7, respectively, were non mesomorphic and showed only melting transitions.