Polyene

Polyenes are poly-unsaturated organic compounds that contain one or more sequences of alternating double and single carbon–carbon bonds. These double carbon–carbon bonds interact in a process known as conjugation, which results in an overall lower energy state of the molecule.

Normally carbon–carbon double bonds which are not conjugated or only conjugated with only one or two other carbon–carbon double bonds have high enough energy that they absorb in the ultraviolet region of a spectrum, but the absorption energy state of polyenes with numerous conjugated double bonds can be lowered such that they enter the visible region of the spectrum, resulting in compounds which are coloured.

Many fatty acids are polyenes, and many dyes contain linear polyenes. Other examples of polyene compounds include beta-carotene, which is yellow to orange coloured depending on concentration, and polyene antimycotics, some of which are yellow coloured.

In organometallic chemistry polyenes are attached to metal complexes and can be altered through addition to pi ligands.