Lattice simulations of thermochromic distortions in poly(alkylthiophene)s

The thermochromism of poly(3-alkylthiophene)s is explained as a buckling of the main chain by torsions around the inter-ring bonds resulting in a dilation of the π band energy gap. Atomistic simulation calculations show that the necessity to preserve translational periodicity imposes restrictions on the permitted torsions. In our model the effect of heating causes a relative shift of adjacent polymer chains, changing the ring stacking from ‘staggered’ to ‘eclipsed’, in which the chains undergo a spontaneous torsion of 20 °.