A series of chiral thio-and oxo-substituted polythiophenes and polythienylethynylenes has been synthesised and investigated. The replacement of an oxo-linkage by a thio-linkage distorts and/or inhibits the helical aggregation behaviour. The quenching of fluorescence upon coordination to palladium is also radically different depending on the presence of oxo- or thio-substitution of the thiophene units. The alkylthio-substituted polythiophenes and polythienylethynylenes do act as sensors for palladium by quenching of their fluorescence to a significantly greater extent than the quenching observed for nonthio functionalised polythiophenes and polythienylethynylenes.