Synthesis and thermal analysis of disubstituted propiolates bearing terphenylene mesogen

Novel disubstituted propiolates bearing chromophoric terphenylene mesogenic groups, namely, 4′-cyano-4-terphenylyl-2-octynate M(CN) and 4′-methoxyl-4-terphenylyl-2-octynate M(OCH₃) are synthesized, where the terphenyl groups are connected to the C≡C through ester linkage directly. Using transition-metal catalysts such as the classical MoCl₅- and WCl₆-based metathesis catalysts, the polymerization of the M(CN) and M(OCH₃) are carried out in a series of different solution, however, did not obtain any products. It suggests that the WCl₆- and MoCl₅-based catalysts are poisoned by the polar groups, on the other hand, the bulk terphenyl groups and the long alkyl chain around the C≡C bond might inhibit the reaction. M(CN) displays monotropic nematicity, whereas M(OCH₃) exhibits enantiotropic nematicity and smecticity (SmA_d) with a bilayer arrangement when cooled and heated. Ultraviolet spectroscopy and photoluminescence measurements also show that the terphenyl groups endow disubstituted propiolates with strong UV light absorption and high photoluminescence.