"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."
"Organic compounds with two carbon–carbon double bonds are dienes; those with three such double bonds are trienes; those with four are tetraenes, etc."
"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."