Ferroelectric liquid crystal induced by a bridged biphenyl dopant with helical topography

Abstract

A new atropisomeric dopant containing a bridged biphenyl core with helical topography, 3,9-bis[(4-nonyloxy)benzoyloxy]-5,7-dihydro-1,11-dinitrodibenz[c,e]thiepin (2), was synthesized in optically pure form and doped in the liquid crystal host 2-(4-butyloxyphenyl)-5-octyloxypyrimidine (PhP1) to produce a ferroelectric SmC* phase. The polarization power δp of this new dopant is compared to that of an analogous unbridged dopant, 2,2′-dimethyl-6,6′-dinitro-4,4′-bis[(4-n-nonyloxy)benzoyloxy]biphenyl (1), after normalizing for a difference in core transverse dipole moments. Results show that the normalized polarization power of the bridged dopant 2 is greater than that of the unbridged dopant 1 by a factor of 5.3. On the other hand, the SmC* helical pitch p induced by 2 is shorter than that induced by 1 by a factor of 1/6.7. This inverse relationship is consistent with predictions that dopant 2 should have a greater propensity to undergo chirality transfer with surrounding host molecules via conformational core–core interactions. A more direct assessment of the chiral perturbation exerted on the host molecules is achieved by studying the effects of dopants 1 and 2 on the spontaneous polarization induced by a probe chiral dopant, (S,S)-5-(2,3-difluorooctyl)-2-(4-octylphenyl)pyridine (MDW950), which mimics the structure of PhP1.