Discotic mesogens

Chandrasekhar discovered the first discotic liquid crystalline phase in 1977 that was formed by co­lumnar stacks of disc-like hexa-n-alkanoate substituted benzenes.¹ Since then thou­sands of dis­cotic liquid crystals have been prepared and they have attracted much attention over the last ten years because of their extraordinary electro-optical properties.

Figure 1      (A) Phthalocyanine and disc-shape; (B) 4-n-heptyl-N-(4-n-pentyloxy)benzylidene and rod-shape

Discotic mesogens are characterized by their disc-like molecular shape and usually con­sist of a con­jugated macrocyclic or polyaromatic core surrounded by flexible hydrocar­bon chains (e.g. the phthalocyanine derivative in Figure 1).

Many types of core structures have been converted into discotic mesogens such as an­thraquinones, ethynylbenzenes, naphthacenes, perylenes, porphyrins, phthalocyanines, triazines, tetraoxa[8]circulenes, trisoxadiazolylbenzenes, triphenylenes, and tristyrylpyridine derivatives.² The most extensively studied discotic LCs, however, are deriva­tives of triphenylene (Figure 2, B), porphyrin (Figure 2, C), and phthalocyanine (Figure 2, D).

Figure 2      Examples of discotic mesogens (R = alkyl or alkoxy chains)