Triangulene, the smallest triplet-ground-state polybenzenoid (also known as Clar's hydrocarbon), has been an enigmatic molecule ever since its existence was first hypothesized¹. Despite containing an even number of carbons (22, in six fused benzene rings), it is not possible to draw Kekulé-style resonant structures for the whole molecule: any attempt results in two unpaired valence electrons². Synthesis and characterization of unsubstituted triangulene has not been achieved because of its extreme reactivity¹, although the addition of substituents has allowed the stabilization and synthesis of the triangulene core^3,4 and verification of the triplet ground state via electron paramagnetic resonance measurements⁵. Here we show the on-surface generation of unsubstituted triangulene that consists of six fused benzene rings. The tip of a combined scanning tunnelling and atomic force microscope (STM/AFM) was used to dehydrogenate precursor molecules. STM measurements in combination with density functional theory (DFT) calculations confirmed that triangulene keeps its free-molecule properties on the surface, whereas AFM measurements resolved its planar, threefold symmetric molecular structure. The unique topology of such non-Kekulé hydrocarbons results in open-shell π-conjugated graphene fragments⁶ that give rise to high-spin ground states, potentially useful in organic spintronic devices^7,8. Our generation method renders manifold experiments possible to investigate triangulene and related open-shell fragments at the single-molecule level.

Triangulene，最小三重基态polybenzenoid（也称为克拉的烃），一直是一个神秘分子自从它的存在首先假设¹。尽管包含偶数个碳（22个，在六个稠合苯环中），但不可能为整个分子绘制Kekulé型共振结构：任何尝试都会导致两个不成对的价电子²。未取代的三茂铁由于其极高的反应性¹而无法实现合成和表征，尽管取代基的加入已使三茂铁芯^3,4得以稳定和合成，并通过电子顺磁共振测量验证了三重态基态⁵。在这里，我们显示了由六个稠合苯环组成的未取代三茂铁的表面生成。组合的扫描隧道和原子力显微镜（STM / AFM）的尖端用于使前体分子脱氢。STM测量与密度泛函理论（DFT）的计算相结合，证实了三苯并二苯在表面上保持其自由分子特性，而AFM测量则解决了其平面，三重对称分子结构。这种非Kekulé碳氢化合物的独特拓扑结构导致开壳的π共轭石墨烯片段⁶产生高自旋基态，可能在有机自旋电子器件中有用^7,8。我们的生成方法使多方面的实验成为可能，从而可以在单分子水平上研究triangulene和相关的开壳片段。