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

► Non-covalent S⋯O interactions are studied in oligo(thienylene-2,5-dialkoxyphenylene). ► They expected to lead to a better supramolecular order. ► Far-infrared measurements coupled to density functional theory are used. ► The most sensitive modes to the S⋯O interactions are located around 300 cm−1. ► They are assigned to in-plane shear of thiophene rings coupled to the methoxy groups.