EQCM analysis of the alkali metal ion coordination properties of novel poly(thiophene)s 3,4-functionalized with crown-ether moieties

New thiophenes carrying 18-crown-6-ether ring directly linked to the 3- and 4-positions of the thiophene ring were synthesized and polymerized by anodic coupling in acetonitrile. The polymers were characterized by cyclic voltammetry (CV), UV-Vis and FTIR spectroscopy, matrix-assisted laser desorption ionization (MALDI) mass spectroscopy and in situ conductivity. Electrochemical quartz crystal microbalance (EQCM) analysis of the alkali metal coordination ability of the 18-crown-6-ether polymer films in acetonitrile has evidenced that the coordination constants (e.g. 20–80 M−1 for Na+) are ca. two orders of magnitude lower than those of polythiophenes bearing the crown substituents pendant from the polythiophene backbone. The result has been ascribed both to electronic and solid-state effects of the conjugated polythiophene chains.