[3]Triangulene

Other names: triangulene, dibenzo[cd,mn]pyrene-4,8-diyl, Clar's hydrocarbon

C₂₂H₁₂

33/50 uncommon

[3]Triangulene is a fascinating non-benzenoid polycyclic aromatic hydrocarbon with a triangular shape comprising six fused benzene rings. This molecule represents a rare example of a 'Kekulé biradical' – a structure that cannot be drawn with conventional double-bond resonance structures without leaving two carbon atoms with unpaired electrons. First theorized by Erich Clar in 1953, this molecule eluded synthesis for decades due to its unstable nature. Its 'radicals' make it highly reactive and unstable under ambient conditions, quickly degrading through polymerization or oxidation. In 2017, researchers at IBM finally synthesized and imaged individual triangulene molecules on a surface using scanning tunneling microscopy, confirming its predicted electronic structure. The compound appears as deep purple to nearly black crystals when briefly isolated at very low temperatures. Its magnetic properties make it of significant interest for applications in quantum computing, spintronics, and molecular magnetism.