The syntheses of two new terthienyl monomers containing a 1,3-propanedione group and the derived polymers are described along with their electrochemical properties. The conjugation of the terthienyl core with the enol form of the 1,3-propanedione is examined by spectroscopic and electrochemical means. Electronic interaction between the terthiophene moiety functionalized in the 5-position and the 1,3-propanedione is demonstrated. The polymerization conditions are studied with a view to optimizing the stability of the enol form of the 1,3-propanedione group. (C) 2004 Elsevier Ltd. All rights reserved.