Spin characteristics of organic radicals from a single-molecule junction perspective

Organic radicals contain unpaired electrons and represent important open-shell systems for studying molecular spin effects and charge transport. However, conventional spectroscopic and magnetic measurements mainly yield signals, making it difficult to directly resolve intrinsic changes in orbital distribution, exchange interactions and spin state evolution. Single-molecule junctions address this limitation by translating local electronic and spin-related variations into measurable transport responses. In this perspective, we summarize the stable radical scaffolds and radical form tuning strategies relevant to single-molecule junctions. We then discuss how spin distribution, spin coupling and spin states govern orbital structure, molecule-electrode coupling and transport channels, and how these effects are read out electrically. Finally, we highlight opportunities in radical-electrode orbital hybridization, spin-selective transport, control of multiple spin states and radical-based single-molecule functional devices, with the aim of providing mechanistic guidance for molecular spintronic devices.