An atomistic simulation of the effect of pressure on conductive polymers

Two conductive polymers are selected for static lattice and molecular dynam ics methods to determine the possibilities of 'fine tuning' them in order t o achieve desired bandgaps. These are poly-pal-a-phenylene (PPP), consistin g of a pi -conjugated backbone only, and the thermochromic polymer poly(3-a lkylthiophene) (P3AT), which additionally contains flexible side chains. Co nformational changes in both polymers indicate that pressures of similar to 6-7 GPa planarize the main chains. With a sterically hindering atom F in th e ortho site of PPP, conformations a few degrees from planarity may be achi eved at about 20 GPa. The response of the C-H and C-F bonds to pressure is also described. In the P3AT polymer molecular dynamics predicts that above 10 GPa not only does planarization of the main chain occur but the spontane ous 'tilting' observed in the alkyl side chains is also reduced.