Mesophases of Achiral Bent Molecules

Abstract

A systematic structural modification is carried out to change the molecular shapes of stilbene derivatives from rodlike through hockey stick then to bananalike by tuning the length of the functional group attached to the lateral direction of the rodlike skeletons. The mesophases and the corresponding properties are monitored by optical polarizing microscopy, differential scanning calorimetry, electric field effect, and X-ray diffraction. The existence of mesophase is strongly affected by the molecular conformation and intermolecular forces inherited in the moiety employed. Nematic, smectic C (SmC), and anticlinic smectic C (SmCa) phases are formed by the hockey stick molecules. Defects of 2- and 4-brushes are observed for the SmC and SmCa phases and indicate the existence of anticlinic arrangements of neighboring layers. Anticlinic layer structures constitute the intermediate phases between the calamitic and banana mesophases. Electric-field-switched texture changes are evident for the nematic and SmC phases and are different from those of known calamitic mesogens. These behaviors are ascribed to the bent conformation of these hockey stick molecules. Antiferroelectric B2 banana phases are formed by hockey stick molecules with two arms carrying moieties of large enough polarizability.

Thermal Stability on Morphology and Crystal Structures of Hydrothermally Synthesized Titanate Nanotubes and Their Photocatalytic Activity

“…In particular, titanate nanotubes have received a great deal of attention because of large surface area that leads to a wide variety of applications, including secondary lithium batteries, dye sensitized solar cells, catalysts and bio-composite [1][2][3][4][5][6].…”

Self‐Assembly of a Low‐Symmetry Monodendron Containing Two Asymmetrically Linked Molecular Wedges

“…[14] Other examples of low-symmetry molecules are, for instance, banana-shaped [15] and hockey-stick-shaped molecules. [16] Some of the most powerful molecular building blocks for supramolecular (hexagonal) columnar liquid-crystalline phases are 3,4,5-tris(alkyloxy)-, [4,5] 2,3,4-tris(alkyloxy)- [17] as well as 3,5-bis(alkyloxy)- [5] substituted benzene ring motifs of wedgeshaped architectures. In contrast to deformed calamitic molecules with broken symmetry, low-symmetry monodendrons have attracted much less attention so far.…”

On the balance between syn- and anticlinicity in smectic phases formed by achiral hockey-stick mesogens with and without chiral dopants

“…This is in contrast to the case of standard rod-like calamitic molecules whose phase chirality requires molecular chirality. A recently 35 introduced new design concept is to work with an intermediate shape: hockey stick-shaped molecules 2,3 . These are non-straight molecules with two terminal chains, one of which is attached in meta-position to the three-or four-ring calamitic core.…”

“…These are non-straight molecules with two terminal chains, one of which is attached in meta-position to the three-or four-ring calamitic core. Depending on the length of the terminal chains 40 and on the type and direction of the linking groups between the aromatic rings, conventional nematic, SmA and SmC phases can be observed, but also the loss of liquid crystalline behaviour 2,4 . It is a current matter of discussion if achiral mesogens of this type can form chiral phases on their own or 45 not 2,5 .…”

“…Hockey stick-shaped achiral mesogens seem to be unusually capable of generating such a phase sequence, as 60 confirmed by two other research groups. Jones et al 7 found a sequence SmA -SmC -SmC a for a siloxane substituted hockey-stick-shaped compound and Yu et al 2 reported a SmC -SmC a transition for a hockey stick mesogen containing four aromatic rings. Very recently, Yu and Yu presented a series of 65 hockey stick mesogens containing C=C linking groups 8 .…”