Synthesis, Mesogenic and Spectroscopic Properties of 2,5-Disubstituted Thiophene Derivatives

Two series of 2,5-disubstituted thiophene derivatives (series 1: 2,5-bis(p-alkoxyphenylethynyl)thiophene and series 2: 2,5-bis[p-(p-alkoxyphenylethynyl)(phenylethynyl)]thiophene) were synthesized and characterized by ¹H NMR, ¹³C NMR, HRMS and elemental analysis. The relationship between the structure and the mesogenic and spectroscopic properties has been discussed. The results show that compounds 1a–1f all exhibited an enantiotropic nematic mesophase, which was confirmed by the polarized optical microscopy (POM), differential scanningcalorimeter (DSC) and variable temperature powder X-ray diffraction (PXRD). In contrast, the extended conjugated analogues 2a–2b had no liquid crystal properties. As for the spectroscopic properties, incorporating more phenylethynyl units results in red-shifted absorption and emission spectra, greatly enhanced quantum efficiency.