Conformational structure impacts electronic properties

1. Cis and trans polyacetylene, according to the tight binding picture  just presented, should have the same band gap but they don’t!

(as synthesized)

Question: Why not?

(after thermal conversion)

2. Conjugation yields an energy/unit length  which is

minimized with increasing  backbone planarity

3. Rotation breaks conjugation

Structural instabilities and disorder are extremely important (at all length scales)