Synthesis and characteristic properties of poly(naphtho)[2,3- c] thiophene) as a series of fused-ring conducting polymers analogous to poly(isothianaphthene)

Abstract

Naphtho[2,3- c]thiophene was easily obtained as a yellow solid containing 1,3-dihydronaphtho[2,3- c]thiophene as a by-product through dehydration of 1,3-dihydronaphtho[2,3- c]thiophene 2-oxide by refluxing with neutral alumina in deoxygenated methylene chloride solution. Naphtho[2,3- c]thiophene was electrochemically polymerized by a well-known technique to form a thin film of poly(naphtho[2,3- c]thiophene) (PNT) which showed barely perceptible color changes associated with the electrochemical doping at a redox potential of ≈0.69 V versus Ag/AgCl. An opto-electrochemical study revealed that the band gap ( E g) of PNT was 1.5 eV, whereas it had been previously expected from theoretical calculations to be nearly zero eV.