An Atomistic Investigation of Helical Polythiophene

Abstract

An atomistic lattice simulation method invoking bonded, nonbonded and torsional interactions has been used to simulate infinitely long polythiophene helices both as single chains and in a hexagonal lattice. It is shown that while the lowest energy of the polymer is for the all-planar anti conformation (torsional angle ø = 0°), the helical structure becomes stabilised at φ ≈ 170°, provided the variation of the π-component of the torsional energy allows for an energy barrier separating the planar forms φ = 0°, 180°) of at least 0.3 eV, indicating a significant quinoid component, which might result from doping. When the chains form a hexagonal lattice (a ≈ 13.0Å) the helical pitch increases from 7.1 to 11.4 Å as adjacent helices partially ‘interleave’.

Key Words:

• Polythiophene
• lattice simulation
• helix
• conformation