On the Nature of the B4 Banana Phase:  Crystal or Not a Crystal?

Abstract

Bent-core or banana-shaped liquid crystal mesogens are known to form chiral smectic phases from achiral or racemic molecules, representing the first example of conglomerate formation in bulk fluids. The most well studied examples of this behavior occur in the SmCP phases, subphases possessing the B2 chiral layer structure. However, the first description of chirality in the banana phase space was of the B4 phase, whose detailed structure is still under investigation. Indeed, the B4 phase is quite unique, and a consensus regarding the question of whether this phase is crystalline or liquid crystalline has not been reached. Here we describe data showing distinct differences, by NMR, between the SmCP phase and B4 phase of the prototypical banana phase mesogen NOBOW and, based upon an analysis of these data, suggest that the B4 phase is an unusual type of crystalline solid.

Unusual electric-field-induced transformations in the dark conglomerate phase of a bent-core liquid crystal

“…During this process a simultaneous reversal in the polarization and the tilt direction takes place giving rise to a switching from SmC s P A to SmC a P S and SmC a P A to SmC s P S . Bent-core mesogens are well known for the optically isotropic phases they exhibit, which include the B4 phase [7][8][9], the dark conglomerate (DC) [10][11][12][13][14][15][16][17][18][19] and the dark enantiomeric (DE) phases [20]. The DC phase, which is the topic of interest of this paper, is usually found to occur below the isotropic phase.…”

Intrinsic chiral domains enantioselectively segregated from twisted nematic cells of bent‐core mesogens

“…5,6,[15][16][17][18] The spontaneous chirality in the B2 phase originates from symmetry breaking due to the tilt of banana-shaped molecule from the layer normal. On the other hand, in the B4 phase, conformational molecular chirality is believed to be nucleated, resulting in some helical superstructures such as a twist-grain-boundary (TGB) structure with the helix parallel to the layer.…”

Diastereomeric liquid crystal domains at the mesoscale

“…Helical nanofilaments are unique among mesogenic structures with respect to their stability, reproducibility, and controllability. The HNF phase is one of the rare liquid crystal phases that preserves its nanoscale LC structure in a room temperature semi-crystalline state 32 . The nanofilaments can be aligned with self-assembled monolayers 33 , shearing 34 , topographic confinement 35 and controlled growth in a unidirectional director field 36 .…”