Polyene

Cycloheptatriene is an archetypal triene.

Polyenes are poly-unsaturated organic compounds that contain at least three alternating double and single carbon–carbon bonds. These carbon–carbon double bonds interact in a process known as conjugation. Related to polyenes are dienes, where there are only two alternating double and single bonds. Other related class of compounds have three or more double bonds, but they are not alternating with single bonds.

Optical properties

Polyenes are notable because they can be brightly colored, an otherwise rare property for a hydrocarbon. Normal alkenes 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. Thus many natural dyes contain linear polyenes, e.g. beta-carotene, which is yellow to orange coloured depending on concentration,

Some fatty acids are polyenes, and another class of impotent polyenes are polyene antimycotics,^[1]

• Representative Polyenes
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  Amphotericin B is an example of a polyene antifungal (antimycotic) agent.^[2]
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  Leukotriene A4 is a regulator of the immune response.
• 
  Retinal is the chemical basis of animal vision..
• 
  Beta-carotine is red-orange pigment abundant in plants and fruits, notably carrots.
• 
  Polyacetylenes are a synthetic polymer of theoretical interest because they exhibit metallic properties upon oxidation.^[3]

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

References