Trans12polyacetylene

Trans12polyacetylene, commonly referred to as trans-polyacetylene (trans-PA), is the all-trans form of polyacetylene, an unbranched conjugated polymer with repeating vinylene units derived from acetylene. In the trans form, each C=C bond adopts the trans configuration, producing a nearly linear, planar backbone that supports extended pi-conjugation across many repeat units. This geometry contrasts with cis polyacetylene, which is more twisted and less conjugated.

Polyacetylene is formed by polymerization of acetylene under suitable catalysts or oxidative conditions; the trans form is thermodynamically favored and tends to be produced under controlled conditions. Early experiments used metal catalysts and high-pressure methods to achieve high-molecular-weight chains with ordered, crystalline domains. The resulting material is typically relatively insoluble and requires specialized processing. The trans configuration promotes a long, uninterrupted conjugated system that is central to its electronic properties.

Electronic properties of trans-PA are highly sensitive to its doping state. Undoped trans-PA is a semiconductor with a sizable band gap; chemical or electrochemical doping with oxidants or reductants (for example iodine) introduces charge carriers and dramatically increases electrical conductivity, in some cases to metallic-like levels. The conducting state involves quasi-particles such as polarons and bipolarons along the chain, with extended delocalization dependent on chain length and order.

Historically, trans-PA was central to the discovery of conducting polymers. The work of Shirakawa, MacDiarmid, and Heeger in the late 1970s led to a Nobel Prize in Chemistry in 2000. Although polyacetylene itself has processing and stability limitations, it established foundational concepts for organic electronics and inspired numerous derivatives used in devices such as organic LEDs and solar cells. Ongoing research focuses on stabilization, processing, and the development of more versatile, easier-to-handle conjugated polymers.