A polysiloxane based thiourea coupled sensor has been developed for the determination of anions from changes in the UV-Vis or fluorescence spectra. A comparative account of the photophysical properties of the monomer and polymer units bearing the thiourea moiety revealed better fluoride recognition in the polymeric framework. The fluoride recognition by the polymeric senior was attributed to co-operative binding involving a DMSO molecule and a fluoride ion between thiourea groups on adjacent residues. The polymeric sensor can measure fluoride at two different concentration ranges by using either absorbance or emission signalling. (c) 2008 Elsevier Ltd. All rights reserved.