The detection of the linear compound isocyanodiacetylene (HC₄NC) was reported in 2020 by Xue and coworkers and by Cernicharo and coworkers toward TMC-1. Cernicharo and coworkers sought HC₄NC toward the carbon-rich source IRC +10216 as well but did not detect it there. The first group used the 100m Green Bank Telescope for their observations, while the second group used the Yebes 40m telescope. Hyperfine lines of various rotational transistions were resolved in both sets of observations.

Isocyanopolyyne compounds with the formula H–(C≡C)_2n–N≡C are evidently much rarer in space than cyanopolyyne H–(C≡C)_2n–C≡N molecules. To date, the only other isocyanopolyyne compound to be detected is isocyanoacetylene (HC₂NC). Both of the groups that discovered HC₄NC also sought HC₆NC (isocyanotriacetylene) toward TMC-1 but did not find it. In 2013, Vichietti & Haiduke published theoretical predictions of the structures and dipole moments for isocyanopolyynes as large as HC₁₆NC.