A-Level How atoms bond and how that governs a substance's behaviour: worked solution

Question

Polyacetylene is recognised as an organic semiconductor. Account for how polyacetylene manages to behave as an organic semiconductor.

Polyacetylene has a conjugated backbone of alternating single and double C=C bonds, so its p-orbitals overlap continuously along the chain giving a system of delocalised pi electrons. These delocalised electrons are free to move along the chain. The gap between the filled pi (valence) band and the empty pi* (conduction) band is small, so electrons can be promoted across it, allowing electrical conduction - the behaviour of a semiconductor (and doping further raises conductivity).