The authors report the synthesis, optical, and electrochem. properties of a calix[4]arene-substituted polythiophene which demonstrates ion-selective voltammetric, chromic, fluorescent, and resistive responses. The ionochromic response of this polythiophene on exposure to Na+ shows an increased effective conjugation length of the polymer backbone. Despite this, Na+ induces a large pos. shift in the potential at which the polymer is oxidized (greater than +100 mV) commensurate with a large decrease in cond. (>99%). Although the calix[4]arene-substituted polythiophene exhibits no changes in the UV-visible spectrum and only minimal changes in the voltammetric responses on exposure to Li+ or K+, there are large decreases in relative conductivities (69 and 47%, resp.). Thus, although the sensory properties of this polymer are expressed via several measurable entities, the ionoresistive response is clearly the most sensitive. This sensitivity originates from the cooperative nature of carrier transport in a conducting polymers (CP) and is thus inherent in chemoresistive CPs. [on SciFinder(R)]