polien

Polyenes are organic compounds characterized by multiple conjugated carbon–carbon double bonds, forming extended pi-systems. They can be linear, cyclic, or macrocyclic, and their alternating single and double bonds allow electrons to delocalize across the molecule. The degree of conjugation determines the color and light-absorption properties of polyenes, with longer chains absorbing longer wavelengths of light.

In nature, polyenes are common pigments and light-harvesting components. Carotenoids such as beta-carotene, lycopene, and lutein are extended polyenes that participate in photosynthesis and protect organisms from photooxidative damage. Retinal, a polyene aldehyde, is a key light-absorbing molecule in vision. The extended conjugation explains their vivid colors and functional roles in biology, including energy transfer and photoprotection.

Polyenes have significant roles in chemistry, biology, and materials science. They serve as pigments and dyes, and certain polyenes act as antioxidants or light-sensing elements. In medicine, amphotericin B is a notable polyene antibiotic with antifungal activity. In materials science and electronics, long-chain polyenes act as precursors to conductive polymers and other organic electronic materials, where electronic properties depend on chain length and substituents.

Synthesis and reactivity are driven by conjugation. Polyenes can be prepared by building up conjugated units or via biosynthetic pathways in nature. They participate in pericyclic reactions such as electrocyclization, with reactivity and stability closely tied to the extent of conjugation.