Conformational structure impacts electronic properties
2. Conjugation yields an energy/unit length  which is
minimized with increasing  backbone planarity
Si
Si
Si
Si
Si
Si
Si
Si
geminal
s
 bonding
vicinal
3. Rotation breaks conjugation
C
C
C
C
C
C
C
C
C
C
C
C
p
bonding
(as synthesized)
(after thermal conversion)
1. Cis and trans polyacetylene, according to the tight binding picture
 just presented, should have the same band gap but they don’t!
Question: Why not?
Structural instabilities and disorder are extremely important (at all length scales)