[5]Cumulene Bridged Tri(9‐anthryl)Methyl Dimer

Abstract Toward the synthesis and evaluation of stable radical‐based 2D frameworks, a diacetylene‐bridged tri(9‐anthryl)methyl ( TAntM ) radical dimer was designed and synthesized. X‐ray crystallographic analysis revealed a strong spin–spin interaction between TAntM radical units through the diacetylene linker, resulting in a closed‐shell [5]cumulene structure as the stable form. Variable‐temperature (VT) 1 H‐NMR measurements at high temperatures showed signal broadening for aromatic protons, indicating an increased population of thermally excited triplet species as a metastable form. To facilitate spin‐state modulation by external stimuli, mechanical grinding in the solid state was conducted. Due to its reactivity, mechanical grinding partially induced structural changes to radical species in the solid state.