Designing conducting polymer-based sensors: selective ionochromic response in crown ether-containing polythiophenes.

The synthesis and ionochromic properties of polythiophenes functionalized with macrocyclic crown ether groups are described. These polymers are designed to be sensitive to alkali metal ions and chelation of the ion induces a twisting of the polymer’s backbone from planarity. These conformational changes are of interest since they should ultimately lead to cond. changes which can be used to construct new sensory devices. Twisting of the polymer’s backbone from planarity will also reduce the effective conjugation lengths, and polymers in which two of the crown ether oxygens are directly attached to the thiophene rings (I; X = O; x = 1, 2) exhibit large ionochromic responses which are easily detected visually. Only small responses are detectable for I (X = CH2O; x = 1, 2) which exhibit smaller assocn. consts. The large ionochromic responses are mainly the result of twisting at a no. of sites along the polymer chain; however electrostatic factors may also play a role. The ion selectivity is similar to that obsd. for simpler crown ether macrocycles and the smaller rings give the largest response for Na+ ions and the larger rings are most sensitive to K+. [on SciFinder(R)]