Conformational energy studies of the conducting polymer poly(phenylenevinylene)

Poly(p-phenylenevinylene) (PPV) is a conductive polymer with a structure that can be considered an alternating copolymer of acetylene and p-phenylene. This polymer is highly conjugated, and it is this property which is believed to be most important for conductivity. An examination is made of trans-Stilbene as a model for the geometry and orbital structure of PPV. The authors also look at the rotational potential about the Cl-Cl′ double bond and in addition, look at the same potential when the two phenyl rings are rotated by 45 and -45 degrees from the planner structure respectively. This trans-cis isomerization potential is felt to be very important with relation to the electrical properties of PPV. Energy calculations at larger rotation angles would not converge. These results strongly suggest that the cis structure, in which both phenyl rings are planner, is an impossible structure. The major reason for this is probably due to the steric repulsion between H₇ and H₇′.