Guaiazulene, also azulon or 1,4-dimethyl-7-isopropylazulene, is a dark blue crystalline hydrocarbon.

[1] Its low melting point makes guaiazulene difficult to handle, in contrast to the crystalline nature of the parent azulene.

The electronic structure (and colors) of guaiazulene and azulene are very similar.

Guaiazulene is an U.S. FDA-approved cosmetic color additive.

[3] Guaiazulene has applications as a volatile dye with a known evaporation rate to indicate end of use of various products (such as insecticide strips).