Thermal behavior of diynes with formally conjugated heteroaromatic sidegroups

Diynes with heteroaromatic sidegroups directly linked to the acetylenic bac kbone were found to show liquid crystalline behaviour upon heating. Thus, 1 ,4-di(2-thienyl)-1,3-butadiyne, 1,4-di(3-thienyl)-1,3-butadiyne, 1,4-di(3-b enzo[b]thienyl)1,3-butadiyne, 1-(3-quinolyl)-4-(2-thienyl)-1,3-butadiyne, 1 -(3-quinolyl:)-4-(3-thienyl)-1,3-butadiyne, and 5-(2-thienyl)2,4-pentadiyne -1-ol were investigated for their thermal behavior. These diynes also under went polymerization in their liquid crystalline state, although the polymer s so formed did not show liquid crystalline behavior. It was found that the S-atom of the heteroaromatic moieties tends to play a role in making the d iynes show liquid crystalline behavior. Differential scanning calorimetry, thermogravimetric analysis and hot stage microscopy were used to investigat e the liquid crystalline nature of the diynes. All of them showed a nematic liquid crystalline phase upon annealing, whereas smectic phase was totally absent.