An Atomistic Investigation of Helical Polythiophene

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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’.