A class of narrow-band-gap semiconducting polymers

Abstract

Scientific interest in electrically conducting polymers and conjugated polymers in general has been widespread among workers in polymer science, chemistry, condensed matter physics, materials science and related fields since the discovery of doped conductive poly acetylene^1,2. Many doped conducting organic polymers with conductivity spanning the range from insulator to near-metallic ∼10⁻¹⁵–10³ ohm⁻¹cm⁻¹) are now known^1–13. Of prime importance and fundamental interest in the continuing experimental and theoretical search for new conducting, and perhaps superconducting, polymers is the achievement of small or vanishing values for the semiconductor band gap (E_g), which governs the intrinsic electronic, optical and magnetic properties of materials. Existence of a finite E_g in conjugated polymers is thought to originate principally from bond-length alternation, which is related to the Peierls instability theorem for one-dimensional metals1^14–17. Here I describe a novel class of conjugated polymers, containing alternating aromatic and quinonoid segments, whose members exhibit intrinsic band gaps as low as 0.75 eV, the smallest known value of E_g for an organic polymer.