Mesogenic and optical properties of α,α′-bis(4-alkoxyphenylethynyl)oligothiophenes

Liquid crystalline alpha,alpha'-bis(4-alkoxyphenylethynyl)oligothiophenes (bi- and ter-thiophene) have been synthesized and their mesogenic behaviour and optical properties investigated. They all exhibited a nematic mesophase, and compounds with long alkoxy chains also showed lamellar phases. Increasing the number of thiophene units increased both the transition temperatures and the mesophase ranges. As for their optical properties, incorporating more thiophene units results in red-shifted absorption and emission spectra, slightly enhanced quantum efficiency, and a larger Stoke's shift. Most importantly, in terms of the absorption and emission maxima, the incorporation of one 4-alkoxyphenylethynyl moiety was found to be equivalent to adding one thiophene ring.