Mesogen is the basic unit of a liquid crystal , which gives rise to its structural order.
Typically, a liquid crystal molecule consists of a rigid functional group and one or more flexible parts. The rigid part aligns the molecules in one direction, while the flexible parts are responsible for the fluid state of the liquid crystal. This hard part is mesogen. It has a key role in liquid crystal, since the optimal balance of these two parts is necessary for the formation of liquid crystal materials.
In a kalamatic liquid crystal, mesogen is a rod-like structure consisting of two or more aromatic and aliphatic rings joined in the same direction. In a discotic liquid crystal, mesogen is defined as a flat aromatic nucleus that orients molecules in one direction.
These rod-shaped and disk-shaped structures are formed not only by covalent bonds, but also by non-covalent interactions . such as hydrogen bonds , ionic bonds and metal coordination . In such cases, the basic structures that determine the macromolecular forms of the assembled molecules are called mesogens or mesogenic parts.