HIGHLY ORDERED POLY(CYCLOPENTABITHIOPHENES) FUNCTIONALIZED WITH CROWN-ETHER MOIETIES FOR LITHIUM-SENSING AND SODIUM-SENSING ELECTRODES

Functionalized cyclopentadithiophenes 2 and 3 were synthesized and pol ymerized by anodic coupling, in acetonitrile solution, in the presence of 0.1 M tetraethylammonium perchlorate as supporting electrolyte. Th e former carries a 16-crown-5-ether ring coplanar to the bithiophene m oiety, while a perpendicular 15-crown-5-ether ring is present in the l atter. The cyclic voltammogram of poly-2 shows two redox processes at E degrees = -0.3 and +0.3 V, whereas that of poly-3 consists of a sing le response at E degrees = 0.0 V. The difference in electrochemical be havior is attributed to the occurrence of strong polaron pi-dimerizati on in poly-a. The redox potential (E degrees) of this polymer moves to ward more positive values passing from lithium to sodium salts as supp orting electrolytes in acetonitrile solution. The redox cycle of poly- 3 is instead completely insensitive to the change of the cationic spec ies in solution. EQCM analysis shows that (i) both neutral polymers in corporate one alkaline ion per crown ring, (ii) the p-doping process o f poly-a produces the ejection of 50% of the cations, and (iii) comple te cation retention is observed in p-doping of poly-3. These results a re explained by a sandwich-coordination of the cation to the crown-eth er moieties in poly-a following oxidation. Poly-2-coated Pt-wire elect rodes give a linear potentiometric response (slope 60 mV) versus the l ogarithm of sodium concentration, in acetonitrile solution, in the 10( -3)-10(-1) M range.