Structural Effects on Conductivity in Open-Shell Macromolecules

Open-shell polymers offer exciting opportunities for electronic materials, and it is crucial to control the solid-state structure of these materials as their end-use properties depend strongly on the spatial arrangement of radicals. Nitroxide-based open-shell polymers with controlled radical spacing were synthesized through topochemical polymerization. Co-assembly of diacetylene-functionalized gelators with TEMPO nitroxide-functionalized monomers created an ordered gel network that, upon exposure to ultraviolet radiation, polymerized into conjugated polydiacetylenes with a minimum radical separation of < 5 Å. The polymerization proceeds along the well-aligned diacetylene chains, preserving the spatial arrangement of the radicals throughout the fibers. The resulting polymers form extended fibrous networks, where the close proximity of radicals enhanced electronic interactions between neighboring sites. Additionally, the rigid conjugated polymer backbone provided continuous pathways that support efficient charge transport. This combination improved the electronic conductivity to >100-fold that of the starting materials. The interplay of these structural effects demonstrates the importance of nanoscale structural control in tuning the electronic behavior of radical polymers and highlights the impact of molecular organization and polymer backbone structure on conductivity, providing design principles for ordered open-shell polymeric materials with tailored electronic properties.