Aromaticity-Induced Spin State Switching and High-Spin States in Non-Alternant Polyradicals

We present fully $\pi$ -conjugated non-alternant systems, including cases where a topologically tailored degree of freedom expands the set of possible favored spin states. This leads to the possibility of switching the lowest-energy spin state upon a specific geometric distortion. Increasing the delocalization energy in specific electronic configurations via including more (pro)aromatic rings in the polyradical(oid) system without changing the topology can induce a high-spin ground state (GS). The peculiar topology of the presented non-alternant $\pi$ -systems, which has a commensurate effect on GS electronic structure and spin spectrum, usually leading to greater stabilization of open-shell character, is potentially useful for novel compounds with previously unrealized properties for organic electronics, spintronics, biosensors, single-molecule devices, etc. The proposed polyradicals, with one of its derivatives recently synthesized and characterized as a triplet GS diradical, are rationally designed to minimize strain and steric hindrance to make them synthetically accessible and thermodynamically stable, and can be kinetically stabilized by bulky protecting groups at exposed radical sites.