Electrochemical properties and electronic structures of conjugated polyquinolines and polyanthrazolines

The effects of molecular structure on the electronic structure and redox properties of a series of 22 systematically designed conjugated polyquinolines and polyanthrazolines are explored by cyclic voltammetry and spectroelectrochemistry on thin films. The measured electrochemical bandgap of the series of conjugated polymers was in the range 2.0-3.1 eV and found to be in good agreement with the optical bandgap. The oxidation and reduction potentials, ionization potential, and electron affinity of the series of polymers were correlated with their main structural features. All the polyquinolines and polyanthrazolines had reversible reduction with formal potentials of -1.57 to -2.08 V (versus SCE) which make them excellent n-type semiconducting polymers. Polymers containing anthrazoline units have a higher electron affinity by 0.3-0.4 eV than those containing bis(quinoline) units. On the other hand, thiophene-linked polymers have a lower ionization potential by 0.45-0.5 eV than those with phenylene linkages. Thus, thiophene-linked polyanthrazolines combine both low ionization potentials (similar to 4.8-4.9 eV) and high electron affinities (similar to 2.9 eV) and as a result can be p-type and n-type doped to conducting polymers with relatively more stability in air. Spectroelectrochemistry of the thiophene-linked polymers revealed features characteristic of polarons and bipolarons or radical ion dimers. The results suggest that the series of polyquinolines and polyanthrazolines are promising electronic and optoelectronic materials.