The large cyanopolyyne compound cyanopentaacetylene (HC₁₁N) was discovered in the late 1990s by Bell et al., who detected it in TMC-1 via two adjacent rotational transitions measured in the laboratory with a Fourier transform microwave spectrometer by Travers et al. The observations were made with the 43 m Green Bank telescope. Bell had previously claimed the detection of HC₁₁N in IRC +10216 in 1982 and in TMC-1 in 1985 on the basis of estimated rotational transition data that proved to be inaccurate.

With its five C-C triple bonds, cyanopentaacetylene (also known as cyanodecapentayne or undeca-2,4,6,8,10-pentaynenitrile, following IUPAC naming guidelines for nitriles) is very unstable.

Nov 2016 - A publication by Loomis et al. concludes that the claimed detection of HC₁₁N by Bell et al. is not supported by their higher resolution observations.

Dec 2017 - Yet another nondetection of HC₁₁N toward TMC-1 was reported by Cordiner et al..

Feb 2021 - Using spectral line stacking techniques, a secure detection of HC₁₁N toward TMC-1 was reported by Loomis et al.