AN ATOMISTIC INVESTIGATION OF HELICAL POLYTHIOPHENE

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 phi = 0 degrees), the helical structure becomes stabilised at phi approximate to 170 degrees, provided the variation of the TI-component of the torsional energy allows for an energy barrier separating the planar forms (phi = 0 degrees, 180 degrees) of at least 0.3 eV, indicating a significant quinoid component, which might result from doping. When the chains form a hexagonal lattice (alpha approximate to 13.0 Angstrom) the helical pitch increases from 7.1 to 11.4 Angstrom as adjacent helices partially 'interleave'.