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

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 <b>NOBOW</b> and, based upon an analysis of these data, suggest that the B4 phase is an unusual type of crystalline solid.