Evidence for different polymorphisms with and without an external electric field in a series of bent-shaped molecules

Abstract

Five fluid tilted mesophases are observed in a series of achiral banana-shaped compounds. The terminal chain length is the pertinent molecular parameter which induces the polymorphism change. All the phases, refer to tilted lamellar structure without in-plane order in the layers. The observation of monolayer, bilayer, ribbon phase, and undulated structures recalls the richness of the polymorphism of the frustrated polar calamitic liquid crystals. Among the mesophases, we highlight two: a Sm-C G2 phase corresponding to a bilayer structure made of Sm-CG layers, and its two-dimensional variant, Sm- Ctilde; G2. The five mesophases observed at zero field are switchable under electric field. At least three ferroelectric phases are induced by an applied field. There is no direct correspondence between the zero field phases and the phases observed under electric field. These observations show that different polymorphisms exist in the series with and without an applied field. A unique ( E,T ) phase diagram is presented, corresponding to the superposition of the ( E,T ) diagrams obtained for each homolog of the series, where the influence of the chain length is equivalent to a shift on the temperature axis.

Electric‐ and Light‐Responsive Bent‐Core Liquid Crystals: From Molecular Architecture and Supramolecular Nanostructures to Applications

“…The choice for Z and Z is relatively limited, and single atoms (e.g., O and S) and direct bond linkages are most often used. However, ester or hydrogen bonding linking groups were also reported for some bent-core compounds [82,84].…”

“…In the real systems, achiral bent-core molecules 1 (P-n-OPIMBs) [9] and 2 [100,101] exhibiting SmCP phases obviously have opposite polar directions ( Fig. 6.8).…”

“…Therefore, it is also called tristable switching; that is, switching occurring among one AF ground state and two metastable FE states. Some nonsilylated bent-core molecules have been reported to exhibit FE switching mesophases [96,101,[104][105][106][107][108][109][110][111][112][113][114] (see FE switching for silylated bent-core molecules later). This switching takes place between the two energetically identical polar states with opposite chirality or the two opposite orientations of the same state ( Fig.…”

Field‐Induced Switching of Chirality in Undulated Ferroelectric and Antiferroelectric SmCP Phases Formed by Bent‐Core Mesogens

“…In polar smectic A (SmAP) phases [4,5] and in B 1rev phases formed by SmAP-like layer fragments [6] this mechanism is the only possibility for polar switching. There are a few examples that this switching mechanism can also occur in tilted SmCP A phases [7][8][9] as well as in B 1rev phases with SmCP-like layer fragments, [6] mostly under special experimental conditions. Nakata et al [8] and Bedel et al [9] were able to detect this switching mechanism above a critical electric field.…”

“…There are a few examples that this switching mechanism can also occur in tilted SmCP A phases [7][8][9] as well as in B 1rev phases with SmCP-like layer fragments, [6] mostly under special experimental conditions. Nakata et al [8] and Bedel et al [9] were able to detect this switching mechanism above a critical electric field. Schröder et al [7] observed this kind of polar switching only on very slow increase or decrease of the electric field.…”