The detection of 1-ethynyl-cyclopentadiene (C₅H₅CCH) was announced in 2021 by Cernicharo and co-workers. The molecule was detected toward TMC-1 via 14 rotational transitions using the Yebes 40m telescope located in Castilla-La Mancha. 2-ethynyl-cyclopentadiene was also detected via 24 transitions.

The two analogous cyano derivatives of cylopentadiene have also been detected, as has the parent molecule.

Like many astromolecules, the isomers of ethynyl cyclopentadiene isomers are not readily available from chemical companies. Measurements of C₅H₅CCH were performed by McCarthy and co-workers, with the compounds formed by subjecting benzene to electrical discharge. This produces "a rich broth of products" that needed to be carefully analyzed to distinguish the various carriers present.