Control of molecular aggregations by doping in mesophases: Transformation of smectic C phases to smectic CA phases by addition of long bent-core molecules possessing a central strong dipole

Compounds 1−3, each possessing a long bent-rod shape and a central large dipole, were designed and synthesized as dopants which transform liquid-crystal smectic C phases to smectic CA phases. The properties and the layer structures of the dopant molecules in the mesophases were investigated by polarized light microscopy, differential scanning calorimetry (DSC), and X-ray diffraction (XRD). Induction of smectic CA phases from the smectic C phases of compounds 4−7 was performed by doping with a small amount of dopants 1−3. In particular, even 1 wt % (0.5 mol %) of 3c was enough to convert the Sm-C phase into the Sm-CA phase in the case of 4. In addition, matching in the core-lengths was important for the induction. Further, importance of the central dipole was also confirmed by replacement of the CF3 groups of compound 1 with CH3 or H.