Polyenen

Polyene, a term sometimes rendered as polyenen in certain languages, is any molecule containing more than one carbon–carbon double bond (C=C). In organic chemistry the term commonly refers to conjugated polyenes, where double bonds are separated by a single bond and π-electron systems extend along the chain. The term is used for both simple hydrocarbons and more complex structures, including natural products and macromolecules.

Polyenes can be linear or cyclic. When the double bonds are conjugated across the molecule, the system has distinct optical properties, often absorbing in the ultraviolet or visible region. Longer conjugated chains generally have smaller HOMO-LUMO gaps and can exhibit color.

Reactivity: polyenes undergo addition reactions across double bonds; conjugation stabilizes radical intermediates. In polymer chemistry, polyenes can undergo polymerization or serve as monomers in formation of polydienes and other conductive polymers. Biosynthesis of many natural polyenes occurs via polyketide pathways and terpenoid routes.

Biological polyenes: a prominent class is polyene antibiotics (polyene macrolides) that contain many conjugated double bonds in a macrolide ring. Notable examples include amphotericin B and nystatin. They bind fungal cell membrane sterols such as ergosterol, creating pores and disrupting membrane integrity, which leads to antifungal effects. Their use requires careful management due to toxicity to human cells.

In materials science, polyenes are studied as conductive or semiconducting polymers, especially in the doped forms of polyacetylene and other conjugated systems. They underpin research in organic electronics, photovoltaics, and nonlinear optics.