Diradical organic one‐dimensional polymers synthesized on a metallic surface

The synthesis of radical polymers with control over chemical composition and structure is a milestone in materials science and has re-emerged recently because of the development of new synthetic methods to produce stable radical organic compounds. However, their synthesis is remarkably challenging due to the inherent reactivity induced by the presence of unpaired electrons in their structure. Here, we report on the synthesis and characterization of atomically precise one-dimensional diradical peripentacene polymers on a Au(111) surface. By means of high-resolution scanning probe microscopy complemented by theoretical simulations, we provide an evidence of their magnetic properties, which arise from the presence of two unpaired spins at their termini. In addition, we probe a transition of their magnetic properties related to the length of the polymer. Peripentacene dimers exhibit an antiferromagnetic (S = 0) singlet ground state. They are characterized by singlet-triplet spin-flip inelastic excitations with an effective exchange coupling (J eff ) of 2.5 meV, whereas trimers and longer peripentacene polymers reveal a paramagnetic nature and feature Kondo fingerprints at each terminus due to the unpaired spin. Our work provides access to the precise fabrication of polymers featuring diradical character and potentially useful in carbon-based optoelectronics and spintronics.