Triacetylene (C₆H₂) or hexatriyne was identified in CRL 618, the Westbrook Nebula, with the Infrared Space Observatory as reported in 2001 by Cernicharo and co-workers The source is a rapidly evolving protoplanetary nebula. The dectection was based on the presence of an infrared absorption at 16.1 μm assigned to the ν₁₁ band af triacetylene along with a feature at 8.11 μm assigned to the ν₈ + ν₁₁ combination band. The initial detection remained unconfirmed until 2011, when Fonfría and co-workers performed additional observations of the ν₈ + ν₁₁ combination band with the Texas Echelon Cross Echelle Specrograph (TEXES) at the NASA Infrared Telescope Facility (IRTF) on Mauna Kea. The protonated form of triacetylene, C₆H₃⁺, may have been observed in Titan's atmosphere due to the presence of an ion of its mass as detected by Cassini and reported by Vuitton and co-workers in 2007.

Triacetylene has three C–C triple bonds. It is very unstable.