Poly(2,3-dihexylthieno[3,4-b]pyrazine) via GRIM polymerization: simple preparation of a solution processable, low-band-gap conjugated polymer (letter)

Conjugated polymers continue to attract attention due to their tunable optical and electronic properties, which has led to such applications as light-emitting diodes (LEDs), photovoltaic devices, and field effect transistors. Many desirable properties are dependent on the material’s band gap (Eg), which is the energy between the filled valence and empty conduction bands and thus corresponds to the HOMO-LUMO gap of the solid state material. The Eg therefore determines both the lowest energy absorbance of the material and the energy of any potential emission. Lower Eg values also result in enhanced thermal population of the conduction band, thus increasing the number of intrinsic charge carriers, and the lower oxidation potential associated with a low Eg can result in the stabilization of the corresponding doped (i.e., oxidized) state. High-purity pTPs can be easily produced via GRIM methods to give soluble materials with low polydispersities, enhanced processability, and reduced band gaps in comparison to the FeCl₃ polymerized materials. The application of these GRIM-polymerized pTPs to photonic devices has been successfully demonstrated with devices giving spectral response to below 1200 nm