Theoretical study of the influence of thermochromic effects on the electronic structure of poly(3-hexylthiophene)

We analyze the solid-state thermochromic effects in poly(3-hexylthiophene) using the results of Valence Effective Hamiltonian calculations on the electronic structure of isolated oligomer and polymer chains. We first examine the evolution of the geometric and electronic properties with chain length. Both syn and anti conformations are studied and found to yield very similar results. We then focus on the evolution of the electronic structure of poly(3-hexylthiophene) as a function of geometrical modifications induced by thermal disordering of the alkyl side-groups. Our results are consistent with the chains being fully coplanar (conjugated) at low temperature (-60°C); at high temperature (+190°C), most of the conjugated segments are only a few rings long (dimers or trimers) and rotated relative to one another by rather large torsion angles (≈45°-60°).