Monosubstituted thermotropic ferrocenomesogens containing heterocyclic pyrazole

The synthesis and mesomorphic properties of two series of ferrocenyl derivatives, 5-[4-(4-alkoxylbenzyloxy)phenyl]-3-(4-ferrocenylphenyl)-1H-pyrazoles 1a and 3-[4-(4-ferrocenylbenzyloxy)phenyl]-5-(4-alkoxylphenyl)-1H-pyrazoles 1b are reported. Compounds 1a exhibited either nematic (N) or smectic A (SmA) phases, whereas compounds 1b formed N/SmC or SmA/SmC phases depending on the terminal carbon length. The formation of SmC phases in compounds 1b was attributed to better molecular interaction between layers since the ferrocenyl unit was remotely located one phenyl ring away from pyrazole core. In contrast, their precursors, ferrocenyl β-diketonates, were in fact non-mesogenic. A less bent shape formed by ferrocenyl pyrazoles than ferrocenyl β-diketones was believed to be responsible for the formation of observed mesophases. The crystal and molecular structure of 3-[4-(4-ferrocenylbenzyloxy)phenyl]-5-(4-hexyloxyphenyl)-1H-pyrazole (1b; n=6) was determined by means of X-ray structural analysis. It crystallizes in the triclinic space group p-1, with a=11.0725(5) Å, b=12.5514(5) Å, c=14.2085(6) Å, and Z=2. The molecular arrangement was quite consistent with the layer structure observed by powder X-ray diffractometer. The cyclic voltammogram measured for 1 and 2 (n=16) indicated that incorporation of pyrazole group hardly influenced the electrochemical behavior of the ferrocenyl moiety.