Synthesis and properties of novel ferroelectric liquid crystalline polyacetylenes containing terphenyl mesogens with chiral groups

Abstract

Novel ferroelectric liquid crystalline (FLC) polyacetylenes, namely, “side-end-fixed” type of PAM 6 OTPhOR* and “side-on-fixed” type of PAM 3 OCO(TPh)OR* were designed and synthesized in high yields (89.3 and 62.0%), respectively, where the terphenyl was linked at the different positions. The thermal stability of PAM 3 OCO(TPh)OR* is better than PAM 6 OTPhOR* owing to the “jacket effect” from terphenyl pendant linked at the waist position well protecting the main chain from the perturbations. The PAM 3 OCO(TPh)OR* shows enantiotropic chiral smectic A phase (SmA*), but it is noteworthy that the PAM 6 OTPhOR* exhibits enantiotropic chiral smectic C phase (SmC*) responsible for ferroelectric liquid crystallinity. Compared to “side-end-fixed” type of polymer, the “side-on-fixed” type shows better light emitting property, ascribed to the mesogen linked at the waist position has stronger tendency to enhance the main-chain coplanarity. Furthermore, the circular dichroism (CD) spectra demonstrate that the asymmetric force field generated by the chiral center affects the secondary structure of PAM 3 OCO(TPh)OR*. Novel ferroelectric liquid crystalline polyacetylenes (PAM 6 OTPhOR* and PAM 3 OCO(TPh)OR*) containing terphenyl pendants with chiral end groups were synthesized. The “side-on-fixed” type of PAM 3 OCO(TPh)OR* showed enantiotropic SmA*, but it is noteworthy that the “side-end-fixed” type of PAM 6 OTPhOR* showed enantiotropic SmC* responsible for ferroelectric liquid crystallinity. Compared to “side-end-fixed” type of polymer, the “side-on-fixed” type shows better light emitting property ascribed to the mesogen linked at the waist position have stronger tendency to enhance the main-chain coplanarity.