Synthesis and characterization of oligo- and crown ether-substituted polythiophenes - a comparative study

The synthesis of two series of thiophenes substituted with crown and oligoe ther groups either via isolating oxaalkyl chains (2, 7-11) or in direct pi- conjugation (4, 12-15) is described. Electrooxidative polymerization leads to the corresponding crown and oligoether-functionalized polythiophenes P2, P7-P11, and P4, P12, respectively. Their electrochemical and spectroscopic properties depend on the length of the spacer and the type of the ether un it. The polymers reveal a high mean conjugation. A specific and strong infl uence of alkali ions on the electrochemical behavior is found for several p olymers. The selectivities correspond to the match of the cation size witho ut solvent shell and the inner diameter of the crown ether units. Spectroel ectrochemical experiments corroborate that the changes in redox properties are due to a hindered diffusion of the counter anions into the film when th e polymer is oxidized. Due to the structural variation novel materials sens itive to different cations are obtained. Importantly, in these conjugated p olymers chemical information which corresponds to a selective host-guest in teraction of the alkali metal cations and the ether units is transduced int o the change of an electrical signal.