Gas sensor with layer of semiconducting organic polymer|is polymerised from a monomer comprising a five-membered heterocyclic aromatic ring with substituent gps. at the 2 and 5 positions

A gas sensor comprises: a pair of electrodes; one or more semiconducting organic polymers deposited onto and between the pair of electrodes in such a manner as to effect a semiconducting electrical connection between the electrodes; and gas sensitive transduction means.One or more of the semiconducting organic polymers is polymerised from a monomer comprising a five membered heterocyclic aromatic ring with substituent gps. at the 2 and 5 positions.The gas sensitive transduction means comprises means for applying electric signal across the electrodes and detection means for detecting a chosen electrical property in the presence of gas. The heterocyclic ring with substituent gps. at the 2 and 5 positions is also substd. at the hetero atom. The heterocyclic ring is substd. at the 3 position. The substd. heterocyclic ring is pyrrole. The substituent gps. at the 2 and 5 positions are aromatic rings, pref. thienyl or thienyl derivs.. The five-membered aromatic heterocyclic ring monomer is polymerised electrochemically from a soln. contg. the monomer and a counter-ion, pref. BF4 - , PF6 - , C8 H17 SO3 - , Fe(CN)6 3- or CH3 C6 H4 SO3 -.ADVANTAGE - By judicious variation of the substituent gps. on the heterocyclic rings, a range of semiconducting polymers for use in gas sensors can be produced, wherein the response profile of a polymer can be 'fine tuned' to a molecule or class of molecule.