Twin molecules

Twin molecules consisting of oxadiazoles have been made by coupling smaller oxadiazoles such as OXD-7 (17) which was introduced by Saito and Tsutsui [59] to dimers (18). The glass-forming capability was improved with an increase in Tg from 77°C (OXD-7) to 186°C (dimer) [60, 61]. 

A classical type of dimerization of heterocyclic compounds is the formation of a twin molecule consisting of the same fragments. Such a reaction is known for 2-benzopyrylium salts. Thus, the reduction of the 2-benzopyry-lium salt 261 by zinc dust leads to the intermediate radical 262, which is dimerized in situ to the bisisochromene 263 (76KGS999) (cf. Section IV, B). 

The formation of charge transfer (EDA) complexes between suitable components may induce columnar [327-329] or nematic discotic phases [329-331]. Also the formation of intramolecular EDA complexes in twin molecules can influence the mesomorphic properties substantially [310,332]. 

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