Far-infrared spectroscopy investigation of sulfur–oxygen interactions in π-conjugated oligomers

Two π-conjugated oligomer models which only differ from the methoxy groups on the phenyl ring, 1,4-bis(2-thienyl)benzene and 1,4-dimethoxy-2,5-bis(2-thienyl)benzene, have been considered to investigate the intramolecular non-covalent sulfur–oxygen interactions. For this purpose, we used far-infrared measurements coupled to density functional theory based calculations. We found that the most sensitive modes to the sulfur–oxygen interactions are located around 300 cm−1 and they are assigned to in-plane shear of thiophene rings coupled to the methoxy groups.