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

Abstract

The synthesis of two series of thiophenes substituted with crown and oligoether groups either via isolating oxaalkyl chains (2, 7-11) or in direct π-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 unit. The polymers reveal a high mean conjugation. A specific and strong influence of alkali ions on the electrochemical behavior is found for several polymers. The selectivities correspond to the match of the cation size without solvent shell and the inner diameter of the crown ether units. Spectroelectrochemical experiments corroborate that the changes in redox properties are due to a hindered diffusion of the counter anions into the film when the polymer is oxidized. Due to the structural variation novel materials sensitive to different cations are obtained. Importantly, in these conjugated polymers chemical information which corresponds to a selective host-guest interaction of the alkali metal cations and the ether units is transduced into the change of an electrical signal.