Electroactive, pi-conjugated polymers based on transition metal-containing thiophenes

A series of heterocycle-based bis(salicylaldimine) complexes have been synthesized and their electrochemical properties investigated. Both nickel and copper complexes of the simplest ligand 1 (SALOTH) were found to undergo electropolymerization to yield durable electro-active films under oxidizing condition. In both cases polymerization desisted upon blocking of the para position of the phenol ring. Hence, it appears that the polymer formed from complexes 2a-b is comprised of phenylene linkages at this site. In stark contrast when the conjugation of the monomer is extended by utilizing a terthiophene core, blocking of the para (complex 6) and both the ortho and para (complex 7) positions did not preclude polymerization. Furthermore, the metal-based oxidation moves to higher potentials, and additional redox processes, not seen in the other systems, grow in at lower potentials. Thus, we believe the polymer structure in these cases to be that of a polythiophene.